Tuesday, May 31, 2011

Coffee Acidity

One thing was painfully clear at the SCAA show in Houston, acidy coffee is in! Really! I even heard one coffee described as having "aggressive acidity." Dark Roasts are out, Light Roasts are in. Light Roasts are complex, refined, have good acidity. Dark Roasts, well, Dark Roasts just aren't cool anymore. I mean, Starbucks over roasts their coffee. And we all know that Starbucks is not cool. Light Roasts are Third Wave and Third Wave is in.

Along with the trend towards Light Roast is this new found appreciation for Acidity. Acidity is what gives a coffee its brightness, its liveliness. Good Acidity can be likened to carbonation in a soda, without it the beverage is flat. Something I heard repeated time and again was the necessity of educating the customer about coffee acidity. But not all acidity is good, and a lot of what I tasted was acids due to defects in the coffee.

Of the plus 1000 different chemical compounds identified in coffee about 50 or so are acids. Many of these are volatile compounds and diminish in roasting. Light Roasts tend to emphasize these acidic compounds and bring them to the fore. This is why coffee tasters in the import/export trade roast their samples very light to expose these particular defects. Trade Cupping or Defect Cupping is a necessary skill for any coffee professional but one would be remiss into assuming that this is some higher form of taste.

Coffee's acidity comes from a combination of its inherent acidity along with the coffee bean's production cycle: growing, processing, and roasting. Coffee's inherent acidity is chlorogenic acid, which, along with caffeine, is part of the plant's defense against insects. Chlorogenic acid breaks down in roasting into quinic and caffetic acids depending on the amount of time the coffee is exposed to heat. Roasting machines with poor heat transference produce more of these acids resulting in a tinny, bitter taste. I have written more extensively on this acid in "Bitterness and Acidity in Coffee."

One of the more oft quoted acids is Citric Acid. This acid is usually associated with fresh crop coffee and indicates new harvest. Experienced cuppers will tend to opt away from these lots and wait for later deliveries, giving the coffee a chance to mature. If the flavor persists it is an indication that too many immature green coffee cherries are making their way through. I have notice in my own travels that first time cuppers often take a liking to this taste largely due to the fact that it is the first taste that they learn to identify. This acid is less volatile than other acids and so cannot be "roasted" out. Its easy to identify, since most of us are familiar with citric acid from citrus fruits.

Another common acid is malic. I have noticed an increase in this acid over the years as sun grown coffee has become more commonplace. It is due to excessive day/night time temperature deviations. Shaded coffee farms have more stable temperatures which benefits the plants night time expiration. This acid has a distinct tart apple peel taste that lingers on the palette.

Acetic acids come about from the just pulped coffee beans sitting in the fermentation tank. The time in the fermentation tank is critical since the enzymes break down the silver skin on the coffee beans. Too much time, or if the temperature is too high, however, results in a vinegar like taste. Sometimes this is confused with wineyness.

Most of these acids will decrease in roasting, aside from the Quinic, but as more roasters opt for a Light Roast these acids come to define the coffee's flavor. I hear a lot of pontificating about this coffee's blueberry taste, or apricot, plum, or jammy, as if they are talking about their favorite wine. The one thing that these acids have in common is that they invariably lead to a soury cup. You can mask some of these flavors by increasing the brew temperature, but as the cup cools so returns the sour. What's more, these acids tend affect a person's body, resulting in an edgy, uncomfortable feeling. Some assume it is caffeine, but it is these acids.

In my years of roasting I have never had a customer come in and ask for an acidic coffee: you know, something that tastes like fresh squeezed lemons? Something that will sour my stomach and make me feel all jittery?

Maybe its time the customer educated us.

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