IF I’M A HOME ROASTER

 

ROASTING ISN’T ROCKET SCIENCE. IT IS MUCH, MUCH EASIER. IN FACT, IT IS SO EASY THAT ANYONE CAN DO IT, EVEN AT HOME. WHILE HOME ROASTING IS VERY SIMILAR TO WHAT TRANSPIRES IN A COMMERCIAL ROASTERY, THERE ARE A FEW EXTRA TIDBITS THAT MAY BE HANDY TO KNOW IF YOU INTEND TO TAKE YOUR COFFEE HABIT TO THE NEXT LEVEL. BOTH INVOLVE THE TWO ESSENTIAL ITEMS YOU NEED TO MAKE IT HAPPEN: GREEN COFFEE AND A ROASTER.

Acquiring green coffee is pretty easy these days. If you were to walk into a roastery and ask them to sell you small amounts of green coffee, they most likely would do so. There are also a number of different online retailers that will sell you green coffee for home roasting. What really matters with green coffee is storage. While it can be a stable product, with the ability to last relatively unchanged for well over a year after harvesting, it must be stored properly. 

Basically, this means green coffee must be kept dry and at a cozy temperature. If the humidity is high, the coffee will absorb moisture. If it absorbs enough moisture, microorganisms may start chomping on it and growing, running the risk of ruining the coffee. Higher moisture contents may also facilitate natural degradation of the green bean, as will storing the coffee at temperatures that are too warm.

When green coffee doesn’t age well and it isn’t caused by mold, it develops a flavor known in the industry as “baggy”. It got this name because for most of recent coffee history, green coffee has been stored in jute bags and the baggy flavor tends to be woody/cardboard/grassy, not so unlike the way we imagine jute might taste. 

Fortunately, storing small amounts of green coffee properly in your home is simple. If the climate in your home is controlled throughout the year to make you comfortable (i.e., you use air conditioning and heating), then the coffee will likely stay fresh for many months, even for more than a year, assuming you don’t store it, say, next to the shower. If the conditions aren’t that controlled, then merely keeping the coffee in airtight containers (plastic, glass, or metal) will also do the trick. 

There’s also anecdotal evidence that storing coffee in the freezer is an excellent way of preserving it with no known side effects (while crystal formation doesn’t seem to be a problem, the same risks that apply to storing roasted coffee in the freezer would apply to green coffee, as well). 

Once you’ve got the green bean storage situation figured out, all you need is something with which to roast them! As a home roaster, you will be constrained by the tools available, thus, don’t expect to be manipulating the roast profile too much; home roasting machines aren’t as sophisticated as commercial machines. 

This isn’t to say you can’t create an excellent coffee at home, just that you may not get to explore the finer points of roasting too much. You can roast coffee with pretty much any tool you have that will transfer heat to the coffee. Most people start roasting coffee at home the way it is typically done in Ethiopia— on a skillet or other heated pan. 

This works, but roasting the beans evenly is very tricky, even with constant stirring. Other people start with hot air popcorn poppers. They hold only a small amount of coffee but hot air is a very efficient way of transferring heat to coffee. Commercial air roasters do exist, but they are much less popular than drum roasters, which are just large, metal cylinders that are heated externally and transfer the heat through the drum. If home roasting becomes a bigger part of your life, you can purchase an actual home roaster. 

There are several different types available, each with its own pros and cons. Both air and drum roasters are manufactured. Of course, if you like to work with your hands, you can always just build your own home roaster!

A DARKER ROASTED COFFEE? DO DARKER ROASTS HAVE LESS CAFFEINE?

 

The answer, unfortunately, is not clear. The available data are all over the place. Some research shows that the concentration of caffeine increases with darker roasts while other research shows that it decreases. Some research even shows no changes at all! What are we to make of all this—how can we see completely opposite patterns with something that seems so cut and dry? If we consider what we know about roasting and add to it some details of how caffeine behaves in the universe, we might be able to guess at the answers. 

As coffee is roasted longer and darker, it loses mass: gaseous molecules are created during roasting and they leave the bean. Longer roast times produce more gases, which mean lower weights. Some molecules in the beans, however, don’t change at all during roasting. Consequently, as roast levels darken, these static compounds increase in concentration. We can demonstrate this with an example using mythical compound q. Let’s say the concentration of q in the unroasted bean was 5 parts q to 100 parts bean. 

In a light roast, some of the bean vaporizes leaving only 85 parts bean but q stays the same. So, now the concentration is 5 q/85 bean. If the roast darkens a lot, the bean may only have 75 parts left, making q much more concentrated merely because it could tolerate the heat! This behavior would certainly help explain how the concentration of caffeine increases in darker roasts. Its actual content remains constant while lots of stuff around it is leaving. If this were always the case, then we’d always see an increase in caffeine concentration with darker roasts. But, that’s not what we find. Caffeine seems to be a fairly stable molecule in coffee. In other words, it doesn’t seem to combine or interact with other molecules, though there isn’t any research exploring whether this is true or not. 

However, it does have a quirky trait whereby it tends to not obey the typical transition steps between phase changes. So, instead of changing from a solid to a liquid to a gas, it often skips the liquid phase and turns directly into a gas, a process called sublimation. Sublimation for caffeine can begin at 178°C (352°F). While it is very difficult to measure the actual internal bean temperature during roasting, it is simple to measure the temperature of the mass of beans, which is probably near the temperature inside a bean. 

As most roasts easily exceed bean mass temperatures of 215°C (419°F) and can go as high as 235°C (455°F), it is perfectly reasonable to suspect that some caffeine in the bean sublimates and drifts away from the bean. If this happens, then it explains the caffeine decrease as roasts become darker. In fact, some research does indeed show that total caffeine content decreases with darker roasts. 

What about the data that demonstrated no change in caffeine concentration in either direction? Well, it is possible that both of those phenomena occurred simultaneously at just the right levels as to maintain a constant caffeine concentration. I don’t think it is that straightforward, though. 

There are several reports where beans were processed differently or were of different quality grades and their caffeine contents were different. This suggests that some kind of interaction between caffeine and biological and/or chemical processes exists. The effect of this interaction may be the unpredictability of how caffeine behaves during the roasting process. At the end of the day, all this discussion of how the caffeine concentration is changing is probably moot. In all cases, the changes in concentration are pretty small, amounting to 0.1 percent or less of a difference from the lightest to the darkest roast.

 Thus, in a practical, real-world sense, on a per-cup basis, the amount of caffeine in a cup produced from a very light roast compared to that of a cup produced from a very dark roast is pretty small. It is so small, in fact, that a person who drinks a cup of coffee a day would probably experience no physiological difference between the two cups based upon their caffeine content! 

HOW IS COFFEE DECAFFEINATED?

MORE THAN A FEW PEOPLE OUT THERE CAN’T FUNCTION WITHOUT A CUP OF COFFEE A DAY, IF NOT TWO OR THREE CUPS. MOST COFFEE DRINKERS NOT ONLY RELY ON THE CAFFEINE IN COFFEE BUT THEY RELISH THE ENERGY AND AWARENESS IT BRINGS. HOWEVER, THERE’S A DEDICATED GROUP OF DRINKERS WHO EITHER DON’T WANT THE CAFFEINE OR PHYSICALLY CAN’T TOLERATE IT. SO, THEY DRINK COFFEE FROM WHICH THE CAFFEINE HAS BEEN REMOVED.

As of now, there are no arabica varieties in cultivation with caffeine content that 68 meets international standards for what constitutes decaffeinated coffee. Thus, all decaf coffee comes from manually removing it from ordinary coffee. There are four commonly used solvents for doing this: methylene chloride, ethyl acetate, carbon dioxide, and water. No matter which solvent is used, the beginning of the process is the same. Green coffee beans are steamed or soaked in water to make the caffeine more available to the solvents and to make it easier for the solvents to penetrate the beans. From here, two main pathways exist: direct solvent extraction or indirect extraction. 

In direct extraction, where methylene chloride and ethyl acetate are used, the wet green beans are treated directly with the solvent for some eight to twelve hours. Then, the solvent is removed and the beans are steamed (to help drive off any remaining solvent) and dried before roasting. Unfortunately, these solvents don’t extract just caffeine. Thus, other compounds, which may be related to quality, may also be extracted. This is one reason why decaf has a historically bad reputation for quality (the other reason is that low quality coffees were often used: junk in, junk out). 

Carbon dioxide is a terrible solvent for caffeine under normal conditions as the solubility of caffeine in it is low. This is not surprising, as carbon dioxide is a gas at room temperature! However, if carbon dioxide is taken to its supercritical state— where it has liquid and gaslike properties simultaneously—it improves, and if a bit of water is added, it becomes much better. To take carbon dioxide to its supercritical point requires special equipment to significantly increase temperature and pressure. The great benefit is that supercritical carbon dioxide seems to selectively extract caffeine and not much else. 

The indirect method allows for water to be the only solvent in direct contact with the beans. Water can be used to extract the caffeine and other compounds and then the water solution is treated with a solvent or passed through a filter to remove the caffeine, pulling it away from the beans. The other compounds can then be returned to the coffee beans before drying them down. When water is the only solvent used, a clever trick is employed to prevent compounds other than caffeine from being removed. 

The process begins with soaking the wet green beans with water and then removing the caffeine from the solution, as in the indirect method. Then, the beans are discarded! The solution, sans caffeine but with the other stuff, is then the solvent used to extract the caffeine from the next batch of coffee. Doing it this way means very little noncaffeine material is extracted by the solvent. Now, nothing has to be returned to the coffee and it is believed that the end result tastes better. 

There will always be a place for decaf coffee, as there will always be someone who loves the taste of the coffee at all hours of the day but doesn’t want to deal with the physiological effects of the caffeine. Modern decaffeinated coffees can have excellent quality. Like all technology, the methods for removing caffeine are continuously improving. Thus, expect the quality to improve even more. “I was taken by the power that savoring a simple cup of cof ee can have to connect people and create community.”

HOW DO I KEEP MY COFFEE FRESH?

 

YOU JUST PURCHASED A BAG OF COFFEE AND YOU NOTICE THAT JUST A LITTLE BIT ABOVE THE MIDWAY POINT OF THE BAG THERE IS A SMALL HOLE! IF YOU SQUEEZE THE BAG, YOU HEAR GAS ESCAPE THROUGH THE HOLE AND, HOPEFULLY, YOU SMELL SOMETHING WONDERFUL. 

WHY ON EARTH IS THERE A BELLY BUTTON ON THE BAG? YOU ALREADY KNOW THE SIMPLE ANSWER: TO LET OUT AIR. OF COURSE, IT IS MORE COMPLICATED THAN THAT. THAT HOLE IS PART OF A BIGGER DISCUSSION OF COFFEE FRESHNESS AND HOW BEST TO STORE ROASTED COFFEE TO MAINTAIN FRESHNESS.

Presumably, since we know the major factors that cause coffee to stale— gas evolution, high temperatures, oxidation, and humidity—we ought to able to control them to extend the shelf life of the coffee. By teasing some of the data available in the myriad of research on the topic, we can make some general statements that will help. However, without direct research to support our hypotheses, and the ones of the coffee industry at large, some of our conclusions will have to be educated guesses.

Let’s address each staling factor individually, starting with gas evolution. Since smaller coffee pieces allow the release of more gas, keeping the coffee as intact as possible will help. Thus, grinding coffee ahead of time is a poor practice. Rather, grinding should occur just prior to brewing. The other potential way to slow down gas evolution (and all chemical reactions) is to decrease the storage temperature; cooler temperatures slow down chemical reactions and chemical mobility. Thus, storing coffee in the refrigerator or freezer will accomplish this. Unfortunately, I can’t find any sensory data that explores specific taste changes when stored at cooler temperatures. 

Coffee geeks abhor the idea, but, at best, they have some personal, anecdotal evidence to support it. Freezing coffee could run the risk of creating crystals that could shatter cells, much like grinding. Freezing could also lead to freezer burn, which probably isn’t a flavor anyone wants to introduce to a coffee. Arguably, the biggest reason not to store coffee in the freezer is the risk of condensation forming on the beans as the beans come out of the freezer. This water may then lead to a deterioration of the quality by hastening the natural staling of coffee when the coffee is out of the freezer or by allowing ice crystals to form on the coffee if it is returned to the freezer. Refrigeration doesn’t run the risk of crystal formation, but the condensation is still an issue. 

Ultimately, individual drinkers will have to decide this on their own, at least until some new research surfaces. Preventing or minimizing oxidation reactions is as simple as keeping oxygen away from the roasted coffee beans. Of course, with the atmospheric concentration of oxygen at about 21 percent, that isn’t so easy. Simply putting just-roasted coffee in an oxygen-impermeable container and sealing it doesn’t solve the problem since the air trapped in the container is full of oxygen. Besides, even if coffee were sealed up in a container, the container would likely explode as a result of the pressure build-up from all the volatile compounds being released! So, either the air has to be completely sucked out of the container before it is sealed or all the air must be replaced with a gas that is completely inert, like nitrogen.

I have no knowledge that any company packages just-roasted coffee and then evacuates the air before sealing it, though it seems like a worthwhile strategy. Many larger roasters do flush bags with nitrogen before sealing them. Some research supports this as an effective means of extending the acceptability of the coffee farther from the roast date than by using normal air. Lastly, controlling the amount of water coffee is exposed to is fairly simple. If the coffee is packed in an oxygen-impermeable container, then the container is also likely to be water impermeable. After the container in opened, keeping the coffee in an air-tight container that is waterproof should help minimize exposure to any humidity in the air, although, if the air was full of moisture when the coffee was sealed or closed in a container, then the container won’t offer any protection.

So, what’s the story with the bag and its belly button? The bags that have them are made out of oxygen-impermeable materials. Generally, they prevent many gases from passing through. Thus, as mentioned before, if freshly roasted coffee is sealed in a bag, it is liable to explode. The belly button, more formally known as a one-way valve, is a crafty device that allows gas to exit the bag but prevents any gas from entering. It is a release valve; the carbon dioxide and other volatile compounds can escape but oxygen cannot enter. The one-way valve is a fantastic tool but it has its limitations. 

For one thing, unless the air trapped in the bag while sealing it is replaced with something inert, preventing oxygen from entering is irrelevant; the bag is already full of it (though the valve still prevents the bag from exploding). Secondly, once the bag is opened by the consumer, any internal protection is lost and the consumer must repackage the coffee as best as possible. Ultimately, we aren’t able to prevent the staling process from occurring. At best, it can be delayed. However, if coffee is drunk within a few weeks of roasting, the need to delay staling is most likely unnecessary. After all, the freshly roasted coffee will still be pretty fresh!

WHAT DO YOU MEAN BY COFFEE FRESHNESS?

WE ALL WANT THE BEST POSSIBLE EXPERIENCE FROM OUR COFFEE. OBVIOUSLY, THIS MEANS IT OUGHT TO BE FRESH. THAT SOUNDS GOOD, OF COURSE, BUT WHAT EXACTLY DO WE MEAN BY FRESHNESS? 

The implication is that at one point in time, coffee is fresh but it loses that freshness and becomes stale. Ultimately, we’re talking about a taste in the coffee that changes from good to less good because it changes over time. Each coffee drinker probably has a different standard for what level of staleness is unacceptable. That standard is based on their past experience, their level of sensory acuity, and any number of things that might influence their sense of freshness. 

So, for a well-trained coffee geek, staling may be noticeable a week or two after roasting, while for a less discriminating consumer, it may be two to ten months before they notice (or care) about a change in the taste due to staling. 

Thus, there is no absolute definition, so we must discuss the issue with some generalities and wiggle room. The next step is to consider freshness in light of coffee chemistry. We’ve established that roasting has an immense impact on coffee but it actually extends beyond the end of the actual roast. The bean not only passively changes but chemical reactions continue to occur. Some researchers have attempted to correlate these chemical changes to sensory response. 

While some insight has been gained, there are so many factors to account for that we only have a glimmer of the whole picture. During roasting, many gases, or volatile compounds, are released or generated. The end of the roasting process doesn’t mean the volatiles are no longer present. You know this intuitively because anytime you smell coffee, you smell a gas that’s been released and is no longer in the bean. 

In the first twenty-four hours after roasting, the bulk of gases, composed mostly of carbon
dioxide, are released from the bean. Over the course of several months, more and more volatiles escape from the bean structure, which is why coffee smells less intense over time. These volatiles that you smell are volatiles that you won’t be drinking. 

Thus, the loss of these volatiles is a primary cause of staling. Since the volatiles are trapped in the bean and must diffuse out, the size of the bean particles play a significant role on their evolution. Smaller particles, with more surface area relative to their volume, offer much shorter distances for the volatiles to travel. If coffee is ground just after roasting, 26 to 59 percent of the carbon dioxide (and undoubtedly other volatiles) will be released immediately, with the larger value coming from smaller bean particle sizes that have a larger surface area to volume ratio. 

The other primary cause of staling is the oxidation of compounds within the bean. While lipids (fats and oils) have been the main purview of coffee oxidation research, other molecules react as well and are surmised to play a role. Independent of the identification of specific oxidation reactions, the data demonstrate that coffee exposed to oxygen stales quicker than coffee not exposed to oxygen. 

An indirect factor in coffee staling is ambient temperature. Higher temperatures increase the rate of chemical reactions. Thus, the warmer the room, the faster gas evolution and oxidation will occur. Also, higher levels of water activity (essentially, the amount of water available to participate in chemical reactions) hasten staling. In other words, exposure to humidity will allow coffee to absorb moisture, permitting bad things to happen. 

While many a coffee geek suggests light is detrimental to coffee freshness, there is no evidence to support this in the literature. However, as some wavelengths of light contain enough energy to break chemical bonds (think UV and some plastics), it is reasonable to moot that light can play a damaging role. 

Researchers working on coffee staling chemistry have identified a number of volatile compounds that either correlate with negative aromas or with negative aroma experiences. Unfortunately, there is no agreement on any one compound or even the ratio of two compounds that guarantees a successful measure of staleness. Part of the challenge is that the roast profile, roast level, and coffee origin all influence the volatile composition and thus makes finding definitive staling compound proxies difficult. 

Interestingly, very few experiments that test the taste of coffee freshness (without any chemistry component) seem to exist. Some use untrained panelists (i.e, regular consumers) as their assessors while others use trained panelists to collect more refined data. As there are so few studies from which to draw conclusions, there isn’t much of a story to tell. Moreover, each study had a very unique purpose; generating data to help populate this section of the book was not one of them. 

Thus, the next paragraph is going to be a bit vague. Average consumers, it seems, have a hard time telling the difference between coffees that are fresh or just a few weeks old, whether they were stored on the shelf or in the freezer. In other words, sometimes they can tell a difference and sometimes they cannot. This suggests that coffees that are less than a month from the roast date are probably perfectly acceptable to most consumers. 

On the other hand, with coffee far from the roast date (nine or eighteen months), a trained panel can easily describe differences between the coffees. Whether those differences are important (it was descriptive data, not preference data) was not evaluated. 

A trained panel also seems to be able to identify coffees that were stored under different conditions or are of different ages starting around three weeks from the roast date (there was no statistical analyses in these reports, so it is difficult to be definitive here). It is certainly evident that some people can identify the changes in coffee as it ages. 

Unfortunately, there is no one-size-fits-all answer as to what “stale” means in terms of days after roasting, nor do I think there ever will be one. Since the change in taste depends on sensory acuity and personal preference, the answer will always lie with the drinker.

WHAT DO I CALL THIS ROAST LEVEL?

 

AS WE FIND OURSELVES CARING MORE AND MORE ABOUT COFFEE, WE REALIZE THE ROAST LEVEL OF THE COFFEE IS IMPORTANT TO US. SO, WHEN WE GO TO BUY COFFEE, HOW DO WE TELL THE SELLER EXACTLY WHAT WE WANT? UNFORTUNATELY, IT IS A BIT MORE COMPLICATED THAN ANYONE FEELS IT SHOULD BE.

Simply using light, medium, and dark doesn’t make sense because of the lack of agreement of what they mean; one person’s medium is another person’s light. Moreover, light can encompass quite a range of colors. Names like city, full city, French, and cinnamon are just as nondescript, as there’s no standard for what color they actually correlate with. 

Terms like strong, bold, deep, and heavy are even more egregious, as they either refer to the concentration of the brew (strength) or could possibly refer to its viscosity. Clever marketing brought us these terms and every coffee professional wishes these words would vanish from the roast level lexicon. Much to my dismay, I’ve never come across any terminology that works particularly well for describing roast levels. Is there a more objective method that could be used? Yes. In fact, there are several, all of which are imperfect and all of which are distant and somewhat meaningless to the typical coffee drinker. 

We can be referential to the stages of roasting, and talk about roast level as the time before or after first or second crack. To an experienced roaster and especially to one familiar with a particular coffee (different coffees roast differently, as you’d expect), this is a fairly useful method of communicating roast level. However, as the length of the roast and events within the roast are, by definition, dependent on the roast profile, using the cracks as reference points are only useful if there is some knowledge of the profile. 

Another method that is often used by scientists is weight loss. As the roast progresses, not only does the bean expand, nearly doubling in size by the end, but it loses a lot of weight as moisture evaporates and solid matter is converted into volatile compounds that leave the bean. 

Very light roasts will lose around 12 percent of their weight while very dark roasts can lose as much as 30 percent of their weight. The minor drawback to this system is that weight loss depends on initial weight, which is heavily influenced by moisture content. While most green coffees tend to be in the 9 to 12 percent moisture range, not all of them are, and if not stored well, their moisture content can change. A coffee with a higher moisture content will have a greater weight loss than one with a lower moisture content because more water (and the weight it added) will be driven off.

Did you know? The first webcam was built in 1991 by computer scientists to keep track of how much coffee was in the coffeepot in the Trojan Room, a computer lab at the University of Cambridge.

This is fairly minor problem for small roasters because even in the extreme case, the final weight loss between a high to low moisture content coffee will be pretty small. On the other hand, roasters who roast very large quantities of coffees or roast particularly dark may end the roast by quenching the coffee with a fine mist of water. 

While the expectation is that the water evaporates immediately, thereby cooling the coffee quickly, some water may remain and add weight back to the beans. In my opinion, the biggest problem with this as a tool is that training consumers to calibrate colors to weight loss may never be very successful; people just aren’t used to thinking of weight and color as parallel ideas. 

The last method that can be used to talk about roast color is the actual amount of lightness! More specifically, we can measure the amount of light reflected off the bean or grounds and assign an arbitrary number to that particular amount of reflectance. This is already a common practice in the coffee industry, and the arbitrary numerical scale already exists. 

All one needs to make sense of it is a spectrophotometer, a machine that measures the reflectance or transmittance of a specific wavelength of light, and the coding that translates the number to a color. The latter part is simple, as one can create and even buy already-made colored discs that correspond to the numbers. 

The hard part is that spectrophotometers are expensive machines and usually only larger companies purchase them. Just as tricky is the consumer side of things, much like with weight loss, few consumers are going to learn which number corresponds to which roast level. In the end, there is no perfect way of conveying roast level to someone else without showing them the bean. So, we’ll just continue as we always have, using the tools we have on hand. Hopefully, someone will come up with something better someday.

ARE YOU AFRAID OF DARK ROASTS?

 

STRONG. BOLD. DEEP. HEAVY. DARK. THESE ALL TEND TO MEAN ONE THING IN RELATION TO COFFEE: A DARK ROAST. THEY ARE PART OF OUR MODERN COFFEE LEXICON AND, OFTENTIMES, ARE SYNONYMOUS WITH GOURMET OR SPECIALTY COFFEE. 

YET, ALMOST EVERY COFFEE GEEK STAYS AS FAR AWAY FROM DARK-ROASTED COFFEES AS POSSIBLE. ARE THEY REALLY SO BAD WHEN SO MANY PEOPLE SEEM TO LIKE THEM?

We already know that roasting green coffee turns it into something we want to drink. We also know that how one roasts the coffee makes a difference. It shouldn’t come as much of a surprise, then, that the final color of the coffee is relevant to our experience. The final color is really a function of the roast profile, and it is best thought of in that way. However, just referencing the roast color can be valuable as it often correlates to some bean characteristics and sensory experiences. Beware, though, sometimes, the roast profile can have an influence that beguiles the expectation of a particular roast level. 

Coffee roasting is a function of temperature, as is cooking any food using heat. As the temperature of the bean increases and roasting progresses, some chemical reactions continue to occur while new ones come and go. The bean is continuously undergoing chemical changes. Thus, a lighter roast is chemically different than a darker roast; this is well researched by scientists and I’ll spare you the gory details. The only general category of reactions worth mentioning is the Maillard reaction. 

A Maillard reaction is one in which an amino acid (a component of protein) reacts with carbohydrates (often sugars). There isn’t a specific end product from this reaction, especially as the reactions continue to occur; compounds formed from the reaction can react with each other, creating a dizzying array of complex molecules. Maillard reactions are common in cooking and are responsible for much of the browning we’re familiar with. 

Think seared meat and the crust of bread. And of course, think brown in coffee. The brown compounds resulting from this reaction, called melanoidins, are significant in coffee; they can comprise some 25 percent of the solid material in a cup of coffee. They are also the likely source of any antioxidant behavior in coffee. While they likely contribute to the flavor of coffee in some way (no research exists on it), we can only guess at it in a roundabout way. Melanoidin content increases as roasts get darker (no surprise, there!). So, it isn’t unfair to guess they may contribute to our sense of the difference between lighter and darker roasts. 

Recent research on a compound called N-methylpyridinium (N-MP, a degradation product of trigonelline) is also worth mentioning. It seems to be a significant inhibitor of gastric acid secretion in the stomach, potentially preventing nausea or indigestion— something that happens to some unfortunate coffee drinkers. 

As its occurrence is directly related to the destruction of trigonelline, its concentration in coffee increases as roasting progresses. In other words, darker roasted coffees may make for fewer upset stomachs. For most of us, what we most want to understand about coffee roast levels is how 58 they differ in taste. Coffee geeks have strong feelings about the roast levels they think are best and consumers are no different. However, to anyone wanting to try something new, a little guidance might be helpful. The literature repeatedly shows that as the roast level darkens, acidity, fruity/citrus, grassy/green/herbal, and aromatic intensity decrease. Concurrently, roasted, ashy/sooty, burnt/smoky, bitter, chemical/medicinal, burnt/acrid, sour, and pungent flavors all increase. 

That’s a pretty grim picture but only because some of the research examined extreme roast cases. What must be realized is that these flavors occur on a continuum, with the intensity changing as the roast darkens. Underroasted coffee is not very coffeelike. It tastes leguminous, herby, and nutty. This taste happens just after first crack (see the section on coffee as a test tube) and lasts for a brief time. 

Once it is roasted just past that, all the coffee’s soul is laid out for the palate. All the nuance, complexity, and acidity that could be in the taste exist at this point. Very light roasts are like puppies—full of verve and energy and spunk and sometimes just as annoying. As the roast progresses, those flavors might disappear or mature or become tempered. 

Coffee has many faces between very light roasts and approximately second crack. When the second crack happens, the process of roast begins to creep in. Thus, roasted, woody, smoky flavors begin to develop. From there, the process of roast becomes more and more dominate, approaching an end result of a black, charred bean that closely resembles charcoal. There’s no right answer for how light or how dark any given coffee should be roasted. Ultimately, the person roasting gets to decide, and she’ll likely make that decision based on her personal belief of what best exemplifies the coffee in combination with what she thinks her market desires. Give the same coffee to ten roasters, and you’ll get ten somewhat different coffees.

WHY IS A COFFEE BEAN JUST A TINY TEST TUBE?

GREEN (UNROASTED) COFFEE IS NOTHING YOU’D EVER WANT TO CONSUME. IT IS HARD ENOUGH TO BREAK A TOOTH, AND ITS TASTE LEAVES AN AWFUL LOT TO BE DESIRED. IN ORDER FOR IT TO BECOME SOMETHING WE CAN GRIND AND BREW,

FIRST IT MUST BE ROASTED. ROASTING COFFEE, AS IT TURNS OUT, INVOLVES SOME PRETTY COMPLICATED CHEMISTRY.

When we visualize chemistry, it is quite common to picture a laboratory with test tubes and various pieces of equipment. 

Mix the contents of two test tubes together and bam! Something new is created! Rule number one about chemistry: 

if chemicals aren’t in the same space physically, then they can’t react with each other. Rule number two: sometimes, chemical reactions need a little help getting going and being sustained. 

This help can come from external energy (heat, typically) or an enzyme (a molecule that facilitates chemical reactions without being used up in the reaction and without requiring much, if any, energy to push the reaction forward). 

Roasting coffee satisfies both those rules. The bean itself is the laboratory and the cells that make up the bean are the test tubes. The cell walls and the material within the cells comprise the raw ingredients of all the chemical reactions that take place during roasting. 

Roasting provides the energy source that begins and sustains the chemical reactions. While there are enzymes of all sorts in the cells, their role in the creation of what we know of as coffee is poorly understood. Most likely, enzymatic reactions don’t play a significant role in producing the coffee we know and love.

Actually, a coffee cell is more than just a test tube—it is also a pressure cooker. Plant cell walls are thick and durable. Thus, when the contents strive to get out, they cannot do so easily. 

When the cell becomes heated up from roasting, some chemicals change from liquids to gases and some new gases are formed. These gases will take up more space than they did as liquids or solids, so they push against the cell walls, creating pressure, just like a pressure cooker. While the cell walls eventually break from the pressure (more on this later), the increased pressure conditions do help shape the roasting process.

THAT COFFEE WAS EATEN BY AN ANIMAL?

THERE ARE TIMES IN LIFE WHEN YOU WANT CONFIRMATION THAT THE CONTENTS OF A PACKAGE REALLY MATCHES WHAT IS ADVERTISED ON THE OUTSIDE OF THE PACKAGE. 

IS THE OLIVE OIL REALLY FROM ITALY? IS THE SPARKLING WINE REALLY FROM CHAMPAGNE? IS IT TRULY MANUKA HONEY? THE REASON WE WANT TO KNOW THESE THINGS IS BECAUSE THESE PRODUCTS ARE ALMOST ALWAYS MORE EXPENSIVE THAN THEIR ALTERNATIVES. 

Thus, if we’re going to pay more for them, we want to be sure we’re getting exactly what we pay for (the issue of whether they taste as good as they’re supposed to is a topic for another section). How do we prove the product is what it claims to be? Is the coffee really from Kona, Hawaii? In a perfect world, rare, special, or expensive coffees would taste so different that we’d be able to verify their origins upon tasting them. 

But, being able to taste with that level of precision is difficult and it requires extensive knowledge of coffees from all over the world. Moreover, every coffee grown within a particular place must have a shared and globally unique taste. Well, these prerequisites are never all met simultaneously, so, using taste to confirm the origin of a coffee will never work. Alternatively, a government can establish rules and laws for packaging and labeling and expect its citizens to follow them. Most governments do this and they do their best to enforce them with the limited resources available to them. 

However, there are always clever miscreants, and a government’s power doesn’t exist past its borders. What is needed is an objective, product-based method for determining where a coffee was grown. All one has to do is discover the right chemical or combination of chemicals that will fingerprint a growing location. 

If every fingerprint is unique, then one just has to analyze any sample, match it to a fingerprint, and voilà! Sounds easy, right? The actual lab work is usually fairly easy but discovering a fingerprint is incredibly tricky. Many scientists, including this author, have worked  on this problem. Nobody has figured it out yet. 

There are two big hurdles to this problem. One is settling on the right fingerprint and the other is being able to properly analyze the data to ensure everything works correctly. Scientists have tried all kinds of different analytical techniques and markers to build the fingerprint: near-infrared spectroscopy (NIRS), fourier transform infrared spectroscopy (FTIR), high performance liquid chromatography (HPLC), solid phase microextraction— gas chromatography—time of flight mass spectrometry (SPME-GC-TOF-MS), brewed coffee volatiles, stable isotopes, elemental content, molecular compounds, and who knows what else! The aim has been to find a very quick, cheap, reliable method that can detect the right markers. 

Most of these methods and chemical markers suit this purpose well and much of the data is very promising. The data is promising because many of these methods allow the detection of many signals or markers rather than a small handful. They can be 2,000 reflectances of light at different wavelengths, hundreds of volatile compounds, or dozens of molecules. The more markers one has to create a fingerprint, the more likely that fingerprint will be unique. Moreover, the current state of computer power and statistical software packages allows for adequate analysis of all the data, so building a fingerprint and testing its efficacy is relatively simple. 

So, where’s the problem? The problem is twofold. One, there are never enough samples in a dataset to build a truly robust fingerprint. Two, any given bean is, well, complicated! Large datasets are important for statistical power and simply being able to paint the right picture. The statistical analysis used in origin discrimination work requires many samples for the analysis to work well. 

Many studies do the analysis with too few samples and the numbers crunch well, too well, really. The end result is too perfect because so many markers are being used to describe a small set of samples. The data is overfit. Painting the right picture is just as important. If you want to be able to tell a Hawaiian coffee from a Costa Rican coffee from a Rwandan coffee, you need many samples from each location to capture the variation from that location. Now, with eighty-plus countries in the world growing coffee and each country having many individual regions, acquiring enough samples to paint the big picture is daunting. 

As for coffee being complicated, there are just so many things that influence coffee’s chemical composition. These include, but are not limited to, year of production, the genetic makeup, the climate in which it grew, the nutritional health of the plant, the fertilizer regime, ripeness at harvest, cherry processing method, storage of green coffee, age of the green coffee, roasting, blending, and freshness. 

In order for a geographic fingerprint to work, it must be able to account for all these compositional influences every year across many locations! I believe we have the knowledge and capability to build a geographic indicator system. It may never be perfect but it probably could be effective a very high percentage of the time. All we need are time, manpower, and adequate resources. In the meantime, how do we know where the coffee in our cups is actually from? Trust. Trust in all the people whose hands touched that coffee and belief that they acted with integrity.

COFFEE CAN RUST?

 

WHEN THINGS RUST, IT IS ALWAYS METAL THINGS—IRON, ACTUALLY. PLANTS CAN’T RUST AND COFFEE IS NO DIFFERENT. COFFEE LEAVES, HOWEVER, CAN TURN RUST COLORED AND WHEN THAT HAPPENS, IT’S NOT A GOOD SIGN. 

WHEN COFFEE RUSTS, IT IS BECAUSE A FUNGUS, HEMILEIA VASTATRIX, HAS ATTACKED IT AND THE FUNGUS IS SPORULATING, OR PRODUCING SPORES THAT WILL MOVE TO OTHER LEAVES AND INFECT THEM.

There are many diseases that infect coffee, but none are as prevalent and difficult to control as this one. (Coffee Berry Disease is pretty horrible, but it is still contained to the African continent.) Almost every coffee producing region in the world has Coffee Leaf Rust ( roya, in Spanish), and they all struggle with controlling it. The rust attacks the leaves and turns off any activity in a leaf where it touches. Very light infections simply reduce the photosynthetic ability of a leaf. As infections become more intense, leaves die.

If many leaves on a plant are heavily infected, then the plant can lose all its leaves and any fruit that is maturing since there are no leaves to sustain the fruit. The fungus doesn’t actively attack the coffee we drink, it just prevents us from ever  having coffee to drink. 

There are some fungicides that can be used to combat the fungus. However, they are expensive and have to be applied multiple times throughout the season. For small farmers (which make up the vast majority of coffee farmers worldwide), the cost alone can be prohibitive. For farmers with larger tracts of land, the cost is not inconsequential.

Moreover, many farms are planted on steep, mountain slopes that are difficult to walk on. Imagine the difficulty of walking on a steep slope and spraying a pesticide at the same time! With fungicides being a poor option, the best solution is to plant varieties that are (at least somewhat) resistant to the fungus. 

Unfortunately, there are no pure arabica lines that are resistant. In the 1930s, by a highly unlikely fluke of nature, a natural cross between C. arabica and C. canephora occurred, producing the offspring known as the Timor hybrid. This plant, having genetic lineage of both species, was resistant to the rust. Once it was discovered, it became the center of several breeding programs around the world. 

While the disease resistance was a nice inheritance from its canephora parent, it also inherited some of the undesired taste attributes. So, the breeding programs tried not only to improve its agronomic traits but its quality traits, as well. 

Over the years, other hybrids were discovered or made. These hybrids were, over many generations, bred with pure arabica lines to further improve their taste. Now the world is populated with many of these breeding program offspring. 

The taste of these offspring has never managed to equal that of a pure arabica line, no matter how many backcrosses have occurred. Still, these offspring are rightly called arabica varieties because so much of their genetic material comes from the arabica species. Currently, there are some recent releases that show a great deal of promise in offering rust resistance and desirable quality.

Unfortunately, as with any disease, resistance is not a cure. The fungus is constantly mutating and adapting. Many strains now exist that can attack not only some of the hybrids but pure C. canephora lines, as well. 

So long as coffee is a crop, we will be in constant flux with this and other diseases. It isn’t particularly fun or joyful, but it is the way of life. 

It was a hybrid featuring the genetic lineage from both Arabica and Robusta plants that became the savior for breeding more rust-resistant coffee plants.

WHY DOES A COFFEE PLANT PRODUCE CAFFEINE?

 

Discovered in 1819, by German chemist Ferdinand Runge, the caffeine found in the coffee plant plays a useful role, just not a critical one. 

SO MANY OF US LOVE COFFEE BECAUSE OF WHAT CAFFEINE DOES FOR US. WITHOUT THE CAFFEINE, HUMANITY MAY NEVER HAVE CONTINUED CONSUMING COFFEE AFTER THE FIRST INITIAL TRIES. 

(WHAT REASON WOULD WE HAVE HAD FOR STUMBLING ON THE IMPORTANCE OF PROCESSING, DRYING, ROASTING, AND BREWING?)

BUT, WHAT DOES CAFFEINE DO FOR THE COFFEE 38 PLANT? AFTER ALL, IT DOESN’T MANUFACTURE THE STUFF FOR US AND IT REQUIRES ENERGY (AN IMPORTANT COMMODITY FOR ANY LIVING ORGANISM) TO PRODUCE IT.

Caffeine is considered a secondary metabolite. As opposed to primary metabolites, secondary metabolites are not essential for plant growth and development. Rather, they play some useful role, just not a critical one. Caffeine is found in all parts of coffee, from the roots to the seeds and even in the xylem, the upward-elevator organ in plants. 

A number of hypotheses have been posited for what caffeine can do for the coffee plant. It could be an allelopathic agent, an anti-herbivory agent, a form of nitrogen storage, and/or a pollinator stimulant. Allelopathy is plant chemical warfare against other plants. Some plants produce chemicals that can harm or kill seeds or plants, typically of other species. These compounds, spread by the decomposition of leaf litter or exudation by roots and seeds, influence the population dynamics of plants within a community; not all allelochemicals kill all plants. 

Many researchers have demonstrated that caffeine is toxic to a number of different plants. However, nobody has demonstrated caffeine’s efficacy in a natural setting. Thus, just because it can kill some other species, there is no guarantee that it would kill competitor plants in the forests of Ethiopia (where it evolved). 

Caffeine is incredibly toxic to some insects and fungi (humans, too, in a high enough concentration). So, it often argued that it is a defense mechanism from critters. This hypothesis is supported by the fact that caffeine is produced in young, developing organs that are more susceptible to insect attack. 

This is a logical hypothesis but it is incredibly difficult to prove. To prove it inconclusively would require two nearly identical coffee plants, with the only difference being that one produces caffeine while the other one does not. Unfortunately, we are technologically incapable of producing these conditions, so the experiment will have to wait awhile. If caffeine did evolve to protect against insects, it was probably targeted against specific African insects. If it had been successful in defending against them, then they are probably so inconsequential as pests that they haven’t ever caught the attention of researchers. 

Since caffeine has been found moving up through a plant and it contains four nitrogen atoms, it is thought that it may simply be a way to store nitrogen until needed for a specific purpose. What little research has been done on this hasn’t successfully demonstrated this function. Lastly, caffeine may be an incentivizing treat for pollinators, particularly honeybees.

Research has shown that honeybees’ long-term memory is improved after having caffeine. Presumably, this would help the bees remember the flower they were enjoying and be more likely to return to it in the future, thus helping the plants to crosspollinate. 

While this is promising research, it has yet to be tested outside the laboratory. In addition, it wouldn’t explain why caffeine is synthesized in all the organs in the plant. We will probably never know why coffee first developed caffeine. If we’re lucky, we’ll find out why it has continued to do so. Of course, from the coffee’s perspective, caffeine production has been a huge success. After all, because of that molecule, the human species has spread the seeds of the plant to nearly every place on the planet in which they could thrive!

CAN YOU TELL ME THE FLAVOR PROFILE OF THE COFFEE FROM LOCATION X?

 

THIS IS A QUESTION THAT EVERYONE ASKS AT SOME POINT. THE WINE INDUSTRY, THE GRANDDADDY OF ALL SPECIALTY FOOD INDUSTRIES, HAS SPENT ITS LIFETIME BUILDING ON THE IDEA THAT WHERE A WINE IS 32 GROWN, REGIONALLY, IS NECESSARILY RELATED TO ITS FINAL TASTE. 

THE TERM USED TO DESCRIBE THIS IS TERROIR. IT IS A FRENCH WORD MEANING “LAND” BUT ALSO “THIS SPECIFIC LAND” OR “LOCAL”. 

IN AN AGRICULTURAL CONTEXT, IT REFERS TO EVERYTHING THAT PLAYS A ROLE IN THE PRODUCTION OF A CROP— INCLUDING SOIL, CLIMATE, AND TOPOGRAPHY. 

THE IDEA IS THAT THE GESTALT OF A PLACE IMPRINTS A PRODUCT AND THAT THE PRODUCT, NO MATTER WHERE ELSE IT IS PRODUCED, WILL NEVER TASTE QUITE THE SAME ANYWHERE ELSE; THIS IMPRINT SUPERCEDES THE EFFORTS OF ANY INDIVIDUAL FARMER. THE COFFEE INDUSTRY (AND TEA INDUSTRY AND CHOCOLATE INDUSTRY) TOUTS THE SAME THING: PLACE IS IMPORTANT.

IS IT?

To answer this, it helps to first understand all the different things that can influence the taste of a coffee on the farm. Well, coffee is a bit unusual in that some relevant postharvest events occur that deserve to be considered. So, let’s consider all the events leading up to the point where coffee can be roasted, as this is where it is a stable, tradable product. 

As has been discussed elsewhere, within the English language, peer-reviewed scientific literature, the following things have been proven to influence the taste of coffee: genetic make-up, elevation (with some equivocation), pests/diseases, cherry processing, drying, sorting, and storage. 

Notice the things we haven’t researched/can’t research, don’t seem to play a role, or don’t have enough information to draw a conclusion on their effect: light levels, health of the tree (having sufficient nutrients and water), soil type, source of fertilizer, exposure to agrochemicals, plant age, and harvesting (though nobody believes this isn’t acutely important). 

A cynical way to summarize our knowledge at this point is that we don’t really know how to produce a good cup of coffee, rather, we just know how to avoid screwing it up. 

Did you know? 

Coffee drinking has no effect on the risk of prostate, stomach, ovarian, and pancreatic cancers. It seems to reduce the risk of liver, kidney, endometrial, head and neck, breast, and colorectal cancers, but it may increase the risk of bladder cancer.

It certainly seems to be the case that where and how a coffee is grown influences its taste. Thus, there is a terroir for an individual farm. Is there a terroir to an entire growing region, though? There are seven categories of things that influence a coffee’s taste, each having multiple variations, some of which might interact with each other, and nevermind the other items we’re agnostic about but might need to be moved up in importance. 

That’s quite a few potential influences. For the idea of terroir to hold true, then all these things must interact in such a way as they can never be duplicated anywhere in the world. Currently, at least eighty-seven countries produce coffee to some extent (not all of them are commercial producers) and most of them have multiple regions growing coffee. 

Let’s say ten regions per country for the sake of our discussion. The International Coffee Organization estimates there are some 26 million farmers in the coffee business, which, even if that were broken into six-member families, would leave 4.3 million coffee farms on the planet. With eighty-seven countries, each with ten regions, distributed amongst 4.3 million farms, the number of farms per region is 5,977. Using these values and assuming

every farmer within a region is doing the exact same things to their farms, for terroir to be true, there would have to be 5,977 unique coffee flavor profiles on the planet that are recognized by tasters.

Did you know? 

There are many ways to go from the fresh coffee seed on the tree to a dried, green coffee bean. Each of them will influence the quality of the coffee. That’s a pretty large number. While it is possible to generate that many combinations of flavors based on the seven known factors mentioned above, it seems unlikely that there is that much nuance in the world of coffee. 

Even more difficult to believe is that all the farmers in a single region—even a single mountainside—are farming in the exact method. This last idea seems the most relevant to me in this discussion. If all these factors can influence a cup of coffee and each farmer has the freedom to farm and process their coffee as they choose, it is very likely that the coffee from individual farms in a region are going to vary from each other. 

If this is true, how true can terroir be? 36 I submit that regional terroir for coffee is an artifact of logistics and we are quickly leaving it behind. The artifact is that for most of coffee producing history, all the coffees from various farms within a region, sometimes even a country, were blended together. This blending occurred post-harvest at the wet mill or at the dry mill. 

When so many individual farms’ coffees are homogenized like this, the taste of the end product will be some kind of average that accounts for all the coffees that went into it. Then, those coffees were stored and shipped together (not always so well), giving them time to change and equilibrate even more because of the time it took to get them to roasters elsewhere. 

Terroir, then, was an artificially created phenomenon that arouse out of the logistics of coffee processing, storage, and shipping, not out of the inherent magic of the climate, topography, and farming. This might just be a semantic argument because it is perfectly reasonable to let logistics be represented in the taste of a place. Yes, at one point, coffees from a country or region in a country probably had consistent flavor profiles and in places that still operate in such a way, these profiles, likely still exist. 

However, the past few decades have seen diversification in the coffee industry which suggests coffee terroir is no longer true. One of the hallmarks of the specialty coffee industry is the celebration of individual coffee farms. Coffees of a particular variety, from a particular farm, that used a particular processing method can be easily found at specialty coffee roasters. 

These coffees are celebrations of diversity within a particular place. Roasters are seeking and finding coffees that they want to be different from the region’s norm. If these special coffees can be found, how can there be an overarching influence of place on the cup profile? The reality is that two farmers, separated by just a fence, can produce very different coffees. 

If this is the case, which one represents the terroir of the region? If there are hundreds and thousands of farmers in a region, all able to do their own thing, then who gets the honor of having their coffee be the poster child for the region? As more and more farmers are able to keep their coffees apart from farmers in their region and strive to produce a rare coffee, the potential of terroir being true falls dramatically. 

WHY DOES MY ROASTER TALK ABOUT CHERRY PROCESSING?

 

AS THE COFFEE SEED IS THE PART OF THE COFFEE CHERRY THAT INTERESTS US THE MOST, WE HAVE TO EXTRACT IT FROM THE FRUIT AND GET IT TO A POINT WHERE IT CAN BE ROASTED. 

ESSENTIALLY, ALL THE LAYERS MUST BE REMOVED AND THE SEED NEEDS TO BE DRIED DOWN FROM ITS APPROXIMATE 50 PERCENT MOISTURE CONTENT TO 9 TO 12 PERCENT MOISTURE CONTENT. WE CAN THEN DISCARD (OR FIND A USE FOR) THE FLESH AND OTHER UNWANTED LAYERS. 

THUS, CHERRY PROCESSING IS A CRUCIAL STEP IN GETTING COFFEE INTO A MUG. WITHOUT IT, THE COFFEE WILL NEVER BE READY FOR INTERNATIONAL COMMERCE.

Exactly how that happens is less important than doing it well. The pulp and mucilage are high in water and sugar content—two attractive resources to microorganisms whose overabundant presence during drying is suspected of negatively impacting the cup quality of the coffee. Minimizing or eliminating their growth is a key aspect of cherry processing. 

Ultimately, individual farmers decide how to process the cherries depending on the available resources, cost of processing, the climate at the time of processing, the potential of a price premium, and/or the desired taste outcome. There are three common methods of cherry processing: natural, pulped natural, and washed. There are variations on these but to go into them all is overwhelming. 

We’ll stick to these three. In the natural process, also known as the full natural or the dry process, the entire fruit remains intact while the seeds are dried. The seeds are not removed until every layer, including the seeds, has been dried. On farms where coffee is harvested mechanically, many cherries are already dry when the coffee is harvested. 

These cherries, sometimes called raisins, can be separated and sold as natural coffee. The pulped natural process is one step removed from the natural process. The cherries are pulped (the skin and fleshy pulp removed) and the seeds, still covered by the parchment and mucilage, are dried. This process sometimes goes by alternate names, but “honey” is the most common.

On average, about 100 gallons (378.5 L) of water are required to produce 20 grams (0.7 oz) of roasted coffee, enough to brew about one 11-ounce (325 ml) cup of coffee.

The washed process (a.k.a. the wet process) removes not only the skin and pulp but also the mucilage before drying down the coffee. There are several ways of doing this. Traditionally, the mucilage is removed by fermentation, either by covering the coffee with water until the mucilage is degraded or simply leaving the coffee to sit and ferment without water (known as dry fermentation). 

The term “fermentation” is used because microorganisms, naturally occurring on the coffee or in the environment, consume the mucilage and degrade it via metabolic fermentation processes, though microbial enzymes also play a role. When the mucilage is completely degraded and removed, we deem the fermentation process complete. The fermentation process takes as few as six hours and as many as forty-eight to complete, though typically it lasts twelve to thirty hours. 

The time required depends on the volume of coffee, ambient air temperature, and temperature of the water (if present) used for soaking. An alternative method uses a demucilager/demucilator to mechanically remove the mucilage just after pulping, eliminating the need for any kind of fermentation before drying. A demucilager forces the coffee into a small space, causing the seeds to rub and push against each other and the sides of the container. The pressure liquefies the mucilage, allowing it to be washed away in a few minutes by the small amount of water added to the process.

Since water is used to rinse the coffee seeds upon completion, we call these coffees “washed coffees.” Whether a washed coffee is fermented or demucilaged, the cup quality tends to be similar. It is well accepted by both the coffee industry and scientists that processing affects the cup profile. A generality on perfectly pampered and accomplished processing on farms where hand-harvest methods are used is that going from washed to pulped naturals to full naturals creates an increasing intensity of sweetness, fruitiness (ferment to some), acidity, and body. 

Some people suggest that the coffees become increasingly complex through this progression. On farms where coffee is mechanically harvested, the results of perfect dry processing on cup quality aren’t as predictable. Natural processed coffees from these farms can be more acidy and fruity than washed coffees, or they can be earthy and/or spicy. “Coffee is a language in itself.”

There are three common methods of cherry processing: natural, pulped natural, and washed. Notably, there is little data addressing how processing affects flavor. The second response is related to water stress. Natural processed coffees accumulate a much larger amount of γ-aminobutyric acid (GABA), a molecule known to occur in water-stressed plant cells. As explained earlier, this disparity exists because the natural processed coffees remain metabolically active for a longer time than the washed coffees. 

These responses indicate a significant amount of metabolic activity that is captured by just a few molecules, and the actual changes within the seeds go much farther than just these molecules. It is reasonable to hypothesize that the differences in flavor from different cherry processes stem from these metabolic processes. Yet, until more research is done, we can only hypothesize as to whether the flavor comes from seed metabolism, a migration of compounds into the seed from the mucilage and fruit, or both.

IS ONE ROUND PEABERRY BETTER THAN TWO FLAT-FACED BEANS?

 

BEAUTY IS IN THE EYE OF THE BEHOLDER. AT LEAST, THAT’S HOW THE SAYING GOES.

 WHEN IT COMES TO PEABERRIES, THOUGH, IT JUST MIGHT BE TRUE. THE TRUTH IS, WE DON’T REALLY KNOW.

Inside the coffee fruit, two seeds typically develop. As the seeds enlarge and mature, they push against each other. The result of this pushing is the flat face of a coffee seed. 

On every coffee tree, a percentage of the cherries contain only a single seed. With no opposing seed in the cherry, the lone seed has no flat face. Rather, it is entirely round, almost pealike. This seed is called a peaberry. The percentage of peaberries on a given tree varies, but most of the time it is 4 to 8 percent. 

There have been several reports, however, of trees that produce percentages from 30 to 35 percent. Why peaberries occur is not known, though many scientists over the years have speculated on a variety of possibilities. These include genetic factors, plant age, climatic conditions, poor pollination, and nutritional deficiencies. Scant research exists that examines any of these potential influences. 

Ultimately, some kind of malfunction occurs at the cellular level, which prevents the growth of the seed. The malfunction could occur prior to fertilization. For example, the pollen tube— an organ that grows from a pollen grain after it has landed on a stigma and whose purpose is to deliver its gamete to the receiving gamete in the flower’s ovule— might be disrupted, preventing it from delivering its package. 

Another possibility is that the gamete reaches its destination, but either the female egg or the ovule itself are inviable, preventing fertilization. Alternatively, fertilization may occur without incident, but the zygote or ovule aborts, leaving an empty chamber behind. What has become clear is that there is a strong genetic component to peaberries. Offspring can produce different percentages of peaberries than their parents. Irradiating seeds with neutrons or X-rays, then letting them grow into plants, increases the percentage of peaberries. 

Even manually cross-pollinating flowers decreases the occurrence of peaberries. Peaberries have captured the imagination of coffee drinkers who seem quite happy to pay a premium for them and roasters are just as happy to supply them. This suggests that there is something different or special about the physiology, biochemistry, or taste of peaberries. 

Unfortunately, there isn’t much research on the subject. Peaberries germinate just as often as their flat-faced brethren. There are studies that show some biochemical differences in the seeds when they are unroasted, but those differences largely disappear after roasting. 

As for taste, no research, complete with statistical analysis, could be found comparing flat-faced seeds to corresponding peaberries. In the literature where their taste is discussed, peaberries are considered to taste the same or inferior to flat-faced seeds, though the research was just anecdotal. 26 An important consideration with peaberries and taste is how they respond to roasting. 

A round, somewhat uniform shape will interact with heat differently than an asymmetric shape. If the heat transfer during roasting is different between the two shapes, resulting in different roast profiles, then a taste difference could arise. If this is the case, then the taste difference is an artifact of roasting, not the internal characteristics of the seed. 

I hypothesize, then, that the taste difference would be fairly small and nothing of the scale usually touted by retailer or consumers. With the potential of no important difference, do peaberries warrant their higher price? As peaberries do only occur in low percentages, they are rare; typical supplydemand curves would suggest a higher price. In addition, while farmers have no control over their occurrence, their maximum potential yield is never reached. 

Each percentage increase of peaberries results in a 0.5 percent decrease in potential yield. This is just a numerical difference. Peaberries tend to be smaller and weigh less than most flat-faced seeds, making the yield, as measured by weight, even lower! Thus, farmers have a sense of being penalized by nature and are keen to make up for the economic loss. 

Finally, at mills where the peaberries are removed manually, there is an added cost of labor for that effort. Although, large mills with lots of equipment typically have machines that sort coffee by size, separating out the peaberries, and these mills incur no additional cost or effort. 

Ultimately, it doesn’t matter if there is a statistically significant difference in the biochemistry or taste of peaberries or whether they cost more to produce. If consumers continue to pay a premium for them and believe them to be better, then they are better, at least in the mind of the buyer.