A Nation of Minions, part 1: Yeast & Booze
How army of yeast transforms juice into wine, cider and beer
People have been enjoying the contribution of yeast and other microbes to create new foods for thousands of years. Evidence for wine and beer brewing date as far back as 8,000 years ago.[1]
The roots of turning juice into alcoholic beverages are not clear, but that should be no surprise. Any container of sugary liquid, like the juice of grapes or apples, is liable to ferment. There are obvious benefits to creating wine and cider from fresh fruit. Fermenting fruit juice allows you to preserve the harvest, and consume it at will. The alcohol in the liquids prevents further spoilage, and creates a safer beverage than polluted water. And, obviously, alcohol is intoxicating. Even though the mechanics of fermentation could only be guessed at before the invention of the microscope, people readily and repeatedly discovered brewing, and transforming sweet liquids into hooch is nearly universal.
Yeast is everywhere. 1,500 species of yeast have been identified[2], living in every nook and cranny on earth. So, where there are fruit trees and grape vines, there’s yeast. When winemakers in, for instance, Italy, crush the local grapes, the local yeast are already in the mix. This is the one of the components of terroir — the French term for the environment responsible for making wines unique. As Rob Molyneaux, a wine merchant and beer brewer[3,4], points out,
“you don’t need to look for the right yeast in Burgundy. It’s already in the vineyards, on the cellar walls, on the tools. It’s as much a part of what makes Burgundy wines unique as the grapes and the climate.”
As the vintners have selected for their preferred grape varieties over the centuries, the yeast has evolved alongside.
And the job that the yeast perform is nothing short of alchemy. The simple sugars contained in the pressed juice are the preferred food of the species of yeast most prevalent in domestic use — Saccharomyces cerevisiae. S. cerevisiae takes one unit of glucose, and delivers two units of carbon dioxide and two units of ethyl alcohol: hooch. The yeast gets something out of the transaction — two units of ATP, the basic fuel of all cellular activity.
Beer is proof that yeast loves us and wants us to be happy. - Benjamin Franklin
Beer, compared to wine and cider, is difficult. Unlike fruit, with its sugars already broken into bite-sized (by yeast standards) pieces, the grains used to make beer are not yeast-friendly. Grains of wheat and barley are seeds, and the starch they contain is constructed of sugars in long chains — chains too big for yeast to eat. So brewers have to turn their grain into a food source simple enough to satisfy the yeast. The brewers’ primary job is to prepare a yeast-friendly meal.
The grain intended for beer is allowed to sprout — but only just. As the seeds begin to germinate, a variety of enzymes are released, whose purpose is to break the starch in the seed into simpler sugars. After two days or so, the sprouting process is arrested by roasting the grain. The roasted grain is added to water, and this mixture is called mash. “As you build a mash,” explained Dave Nabong[3], horticulturalist and beer maker, “bringing it to a boil catalyzes the enzymes to break down the starch.” The enzymes tear the starch molecules apart, leaving soluble sugars. Brewers also add hops — different varieties at for different durations, each contributing to the flavor of the final product. As Dave explains,
“You’ll choose a particular hop and add it at a certain temperature, knowing which aromatic elements will be drawn out. You have to plan your mash, because you can only add, not remove.”
When the mash is complete, the sugary liquid, called wort, is drawn off, ready to be handed over to the yeast.
Brewers make wort. Yeast make beer.
The yeast species S. cerevisiae, is a single species, but comes in a huge number of varieties, much like dogs, or roses. And like dog breeds, each yeast strain has its own characteristics and habits. In addition to producing alcohol and carbon dioxide, as yeast ferments sugars, it produces aromatic molecules that contribute to the brew, a different cocktail of flavor compounds for each yeast strain. Varieties of yeast prefer different temperatures, or stop fermenting at different proportions of sugar to alcohol.
Beer makers may need to employ more than one species of yeast during the fermentation cycle. One yeast variety that turns up in many places is Champagne yeast. This variety of S. cerevisiae, native to its namesake region in France, has some characteristics that make it especially useful. Champagne yeast produces few of the aromatic molecules associated with fermentation. That is, Champagne yeast imparts little flavor of its own. This yeast also tolerates a higher level of alcohol in the wort than other beers. Champagne yeast is often used towards the end of the fermentation cycle, to “finish off” converting sugars into alcohol. And Champagne yeast is sometimes added just as beer or cider is bottled, which traps a little extra CO2 in the liquid, creating a bubbly beverage.
The species of yeast used to make beer and champagne is the same yeast used to make bread — another example of the power of yeast to transform human food. But we know that yeast makes two units of alcohol and two units of CO2 for each unit of sugar. So why isn’t bread boozy? And when did people discover the true nature of yeast, this creature who has been influencing human food habits for thousands of years?
We’ll get there. Meanwhile, the next yeast story is available:
Franken-Yeast: Designing Life, Defining Life
More Reading:
[1]The Life of Yeasts, Herman Jan Phaff
[3] Rob Molyneaux and Dave Nabong brew beer together. Their locally popular Steam Boat Pearl won an award at the 2012 McHenry County Fair (Illinois).
[4] Medium doesn’t support proper footnotes. In this author’s opinion, an article without footnotes is like a meal without a pepper grinder.
