The Barista as A Scientist
Even those who aren’t particularly discerning about their morning cup of coffee can differentiate a good cup from a terrible one. Surprisingly, what separates that good cup from a bad one isn’t a subjective matter of preference; there’s actually some very precise science behind creating a cup of coffee that appeals to the majority of taste buds. From selecting a type of coffee to roasting and brewing, every step that goes into the construction of a cup of coffee plays an essential role in how that eventual cup will taste, feel, and caffeinate. Read on to learn more about the chemistry of coffee which may just provides a few insights that will help you improve the way you brew up one of the world’s most popular beverages.
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HOW COFFEE IS EXTRACTED CAN DRAMATICALLY CHANGE ITS FLAVOR.
Extraction is the process of dissolving coffee grounds in water, something most of us know as brewing, or in the case of espresso, pulling. How the extraction process happens can change the taste of coffee in dramatic ways, and not always for the better. Three factors influence the outcome of an extraction: the size of the grounds, the time that water spends in contact with the grounds, and the distribution of water among the grounds. Making things even more complicated, each method of extraction, from pulling espresso to brewing in a French press, requires different things to make palatable coffee and some methods simply produce better coffee than others. If any of these factors are off for a given method, it will yield coffee that’s bitter and in some cases virtually undrinkable. Why? As coffee is extracted, it first releases acids, then sugars, and then bitters. Brewing for too long, uneven exposure to water, or grinding coffee too fine can mean that too much bitter flavor gets extracted. On the flip side, if extraction is too short or done with coffee that’s too coarsely ground, you’ll get an acidic, watery cup of coffee.
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COFFEE CONTAINS A LOT OF TRAPPED CARBON DIOXIDE.
You might not realize it by looking at them, but coffee grounds actually contain a fair amount of trapped carbon dioxide. Much of this CO2 is released within the first 24 hours after roasting occurs, which means that if you grind, brew, and drink incredibly fresh beans, the taste of the coffee is going to skew acidic and there may be an alarming amount of froth on the top as the CO2 rushes to escape the coffee. For most, this won’t be an issue, but if you’re getting beans fresh from a local shop or are roasting your own then it’s wise to let the beans de-gas and develop a day or two before diving into brewing. If you can’t wait, pre-wet the grounds to help them release some CO2 before starting your brew.
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AROUND 28% OF THE ORGANIC AND INORGANIC MATERIAL IN A COFFEE BEAN IS WATER-SOLUBLE.
Somewhere between a quarter and a third of the material that makes up your coffee beans is water-soluble, though you don’t really want all of it to dissolve if you’re trying to get a cup of coffee that won’t make you cringe. According to most, the perfect extraction rate of coffee is about 19-22%, which achieves the ideal balance of the acidic, sweet, and bitter flavors in the beans.
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FLAVOR IS DIFFERENT FROM STRENGTH.
While we tend to equate the two when talking about our ideal cup of coffee, flavor and strength are actually two very distinct, though directly related, elements of how we experience coffee. Strength, with regard to coffee, is a measure of how many dissolved solids are in the water. For most, the ideal brew strength (or percentage of dissolved solids) is between 1.15% and 1.55%. Flavor is related to the level of dissolved solids as well, but is focused on which dissolved solids are in the brew, describing the balance of the flavor components that have been pulled out of the beans. Ideal extraction rates for flavor are between 19-22%. Confused? Say you have a cup of coffee that’s been overextracted. It will contain a large number of dissolved solids, which makes it strong. The flavor of the coffee will likely be bitter, as longer extraction process has allowed too many of the back-end bitter flavors of the beans to enter the brew.
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ROASTING CHANGES THE AMOUNT OF CAFFEINE IN COFFEE.
Though the change is small, as beans are roasted the do lose some caffeine per volume because the beans expand as they are roasted. If you measure your coffee by volume (by the scoop), this can mean that a darker roast will have a little bit less caffeine than a lighter roast. Of course, things are never that simple with this complex drink. If you measure by weight, darker roasts will have more caffeine per cup than lighter ones. Either way, however, the average person is unlikely to notice the difference and similar changes in caffeine levels can be achieve between different varieties and brewing methods.
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THERE ARE OVER 50 DIFFERENT SPECIES OF COFFEE IN THE WORLD.
Coffee plants come in a wide variety, but surprisingly, we don’t regularly drink more than a couple varieties. Only two, arabica and robusta, commonly find their way into commercial coffee production. Arabica far outpaces the production of robusta, however, as nearly 70% of the coffee sold throughout the world is of this variety. Why? Arabica beans are widely regarded as being of a higher quality (though there are certainly exceptions) than their robusta counterparts and as a result robustas are often relegated to making low-quality blends or instant coffee grounds. Of course, not every arabica will be delicious. Factors like weather, climate, and roasting can and do impact the quality of beans, and many high-quality robustas easily outperform low-quality arabicas in taste.
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COFFEE ACTUALLY CONTAINS LIPIDS, WHICH CAN PLAY A ROLE IN AROMA AND QUALITY.
We often don’t think about fat when it comes to the nutritional content of our coffee, but there are lipids in significant amounts in both of the common species of coffee. Arabica contains 15-17% lipids, and robusta much less at 10-11.15%. Why does this matter? Those lipids play a big role in how the coffee tastes and smells. Many important aromatic compounds are oil soluble, and more oil means a better and more appealing smell. Studies have actually shown that coffee that has higher lipid content is consistently judged as better of better quality than that with less. Of course, there can be too much of a good thing. Concentration of these fatty acids increases over time, and eventually they can cause coffee to take on unpleasant flavors.
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ROASTING COFFEE GIVES RISE TO OVER 800 COMPOUNDS.
Roasting coffee is essential to giving the beans the great complexity of flavor that we associate with a high-quality cup of coffee. Yet it’s not all about taste. A full third of the compounds that are created by roasting coffee are related to aroma. One of the most important reactions that occurs within a bean when it’s roasted is the Maillard Reaction. This reaction is the result of sugars reacting with amino acids, a process which produces not only the brown, roasty color of coffee, but many of the compounds that give it its flavor as well. Without the roasting process, coffee wouldn’t have its unique tastes, flavors, and colors, so its an essential component of producing high-quality beans.
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LITTLE OF COFFEE’S INHERENT BITTERNESS COMES FROM CAFFEINE.
Scientists have discovered that there’s little relationship between the caffeine in coffee and its bitterness. Chemical analyses and taste tests done in 2007 determined that caffeine isn’t the bitter component in coffee, contributing to only 15% of the bitterness you can detect in a cup of coffee. Instead, the culprits behind bitterness in coffee come from two kinds of antioxidants that vary depending on how the beans are roasted. Light and medium roasts are high in a type called chlorogenic acid lactones. If the beans are roasted further, producing a dark roast, these compounds break down into phenylindanes, which cause a lingering, much more harsh bitter taste than the lactones. Scientists also found that the longer you roast the coffee, the most intense these bitter elements get, further reinforcing the need to buy coffee that’s roasted properly.
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A GREAT CUP OF COFFEE BALANCES FLAVOR AND BODY.
We’ve already discussed the meaning of flavor and what it does to create a great cup of coffee, but there’s another element at play, too: body. Body is the sensation of viscosity or heaviness in the liquid, which is part of a beverage’s mouthfeel. In coffee, oil is largely responsible for giving it its body. Roasting coffee for longer periods of time can give it more body, but there is a fine line to walk in terms of quality. Roast too long and the coffee will become too acidic, damaging the flavor. The best beans will balance out this relationship between body and acidity to yield a cup that both feels and tastes good in the mouth.
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COFFEE BEANS DETERMINE FLAVOR, BUT SO DOES WATER.
Coffee is almost entirely water (it makes up 98% of the average brew), so it makes sense that the quality of the water that’s used to make it plays a significant role in the eventual taste and quality of the coffee. For the best quality coffee, you need to use not only the best beans but also pure, filtered water. Studies have shown that the ideal cup of coffee is made with water that contains around 50-100 ppm of dissolved minerals. If you aren’t that picky, a palatable cup can be made with anything less than 300 ppm.
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COFFEE IS A PERISHABLE FOOD.
There’s a tendency to think that because coffee is dried through roasting that it will last for a long time. That’s not the case. Coffee’s flavor peaks a few days after roasting and declines any time the beans are exposed to light, air, or moisture. Because of that, coffee should be stored much like a spice. This means it should be kept in a airtight container in a cool, dark, and dry location. Also like spices, coffee stays fresh much longer when it is ground right before use, so never grind ahead or buy ground coffee if you can avoid it. Even under ideal conditions, coffee should be used or replaced every one to two weeks, or it will start to produce flavors that taste “off” and brew an inferior cup. (published in onlinedegrees.org)