Serving People Serving Coffee Since 2005
Issue link: http://baristamagazine.epubxp.com/i/355136
PROPAGATION, PERSPIRATION, DEDICATION, and fermen- tation: Coffee requires all of it. Most professionals know something about the first three, but how about the last? Fermentation, a nec- essary step on the path from seed to cup, is a complex, fascinating, and—like most other things in specialty coffee—a somewhat con- tested subject. Fermentation is more commonly described in terms of preser- vation: It, along with salting, smoking, and curing, is one of the fundamental ways that humans have been prolonging the shelf life of food and drink for ages. From sourdough bread to injera; from mead to beer and honey wine; from cocoa and tea to, yes, coffee— fermentation is a part of our daily eating and drinking lives, and has been pretty much since Homo sapiens could stand upright. The reasons for fermenting coffee are myriad, and so are the methods used to do it—which is part of what makes it a confusing and easily misunderstood, though integral, part of a coffee's life before brewing. In fact, it's been so confusing and misunderstood for so long, that coffee producers and buyers are really only begin- ning to dip their toes in the waters of experimentation and deep scientific research. Like microorganisms breaking down the tasty carbohydrates inside a coffee cherry, this article aims to break down a little bit of the tough stuff around fermentation, and explore its importance and implication in coffee production: How does this step in the process of coffee's prepa- ration make or break the final cup—or does it? WHAT IS FERMENTATION? In the absolute broadest sense, the word fermentation is used to describe microbial activity on a substance, typically referring to the presence of yeasts and bacteria. The act of fermentation, how- ever, is the work that those microscopic critters do to break down and convert carbohydrates (sugars) into different by-products. In bread, it's the process of yeasts creating CO 2 that allows the dough to rise; in sauerkraut, it's what puts the saur on the cabbage, and allows the potent condiment to last almost indefinitely, while fresh or raw cabbage would eventually mold, spoil, and rot. Most of what we consume as food contains carbohydrates— what we often refer to as "sugars"—which are just as appealing a life-sustaining energy source to microorganisms as they are to macro ones like humans and other animals. When any food that's rich in carbohydrates is exposed to yeasts and bacteria, those agents begin to break down its carbohydrates in an enzymatic pro- cess that converts the sugars into other compounds, most notably different acids, gases, and, in some cases, alcohol. The conversion of those sugars acidifies the food, dropping its pH and thereby protecting it from the types of microbes that cause spoilage and disease—which is why fermented foods last so much longer than fresh ones. The difference between "spoilage" and "fermentation" is a mat- ter of several factors, including, simply, taste preference—some people find kimchi offensive, while others like it as funky as they can get it—and intention. If you accidentally leave a bag of grapes laying around too long and mold grows on the grapes, the deteri- oration of the sugars and other nutrients in that fruit was unin- tentional and undesirable. However, if you were to mash up the grapes and deliberately introduce yeast to them in a carboy (a sort of glass container with a small neck used for fermenting liquids), the microbial activity in the jug and the resulting beverage has the potential to develop pleasant flavors and what some consider a pleasingly intoxicating effect. (Think of it this way: If you get a food-borne illness from something, it was probably spoiled—just remember that getting sick from drinking too much home-brewed wine doesn't count as a food-borne illness.) WHAT DOES THIS HAVE TO DO WITH COFFEE? Just as cabbage needs to acidify in order to become kimchi or sau- erkraut, coffee needs to acidify in order for us to eventually drink it as the beverage we know and love. The first and most fundamental reason for that acidification is to remove the fruit from around the beans, so they can eventually be roasted and brewed. That removal takes place at a mill any time from right after the coffee cherries are picked in a washed process, to up to a few weeks later for a natural, after the fruit is completely dried on the seed, or bean. Each coffee cherry has four basic layers: pulp, or skin; meso- carp (mucilage, which is where fermentation happens); parchment; and seeds. We know that in order to have seeds ready for roasting, those first three layers must be removed at some point over the course of processing. "Coffee is fermented," explains a study of washed coffee published by the Food and Agriculture Organization of the United Nations (FAO), "…to ease the removal of a layer of mucilage from the seed/inner integument to which it adheres." In order to effectively remove that sticky stuff, which encases the coffee seed inside the cherry, both enzymatic and microbial ac- tivity is needed to break down the fruit material, which in turn ef- fectively releases the slimy substance from the outer layers of the seed so that the residue may be removed for drying, hulling, pack- ing, shipping, and roasting. In a washed process, the fruit removal happens through fermentation relatively quickly through exposure in open tanks or under water after the coffee cherry has been har- vested. For naturals, it takes place underneath the pulp as the fruit dries. In both cases, it's generally believed that a combination of enzymes already in the fruit as well as microbes naturally occur- ring in the atmosphere and environment around the processing site do the heavy lifting. One of the main questions in understanding coffee fermentation is whether the enzymatic or microbial reactions are what contrib- ute the most to the process: While there's no question in most of the literature (and there's a lot of literature—and it's very dense) that microorganisms play an important role in fermentation, it's not simply their presence that gets the job done. An often-quoted study by Avallone, et al., published in International Journal of Food Science and Technology (2002) asserts that what microbes contribute is the creation of metabolic acids through the conversion of the sugars in the mucilage, but not the removal of the fruit itself. The acidification instead causes a physical and textural change in the cell walls of the fruit, which is a sort of natural response the plant material has to the presence of pathogens. However you look at it, though, one thing is certain: We need fermentation to happen, and, to some extent, fermentation needs us—or at least that's the second part of the controversy. HOW SHOULD COFFEE BE FERMENTED? The vast majority of coffee produced around the world meets with microorganisms in one way or another, and those tiny actors cer- 53 www.baristamagazine.com