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.