Au Naturel
Not long after yeast is added to chilled wort inside a fermentation tank, the fungi gets down to work. The single cell microorganisms begin to ingest the fermentable sugars converting the beverage to alcohol and also releasing CO2 in the process.
Drinkers owe this bit of information to a French inventor and scientist named Cagniard de Latour who, around 1840, discovered that it was in fact yeast that was adding carbonation to beer. A few decades later Louis Pasteur released a book that studied fermentation and beer and, of course, pasteurization methods.
Over the centuries brewers have been able to cultivate yeast strains to get them to a consistency that is most suitable for beer, says Chris White, president of California’s White Laboratories.
Brewer’s yeast does not produce a phenolic flavor, where as most other strains will. Brewer’s yeast does keep some other enjoyable flavors that White says were selected over the years as brewers worked to perfect batches.
The brewer’s yeast also ferments the right kinds of sugars, where as some strains, White says, will consume all sugars. The yeast also settles to the bottom, which is unique and does not happen in nature. That last point is also a bonus for bottled-conditioned beer.
“They were domesticated by brewers, which is unusual for a microorganism,” he says.
White says that a renewed interest in homebrewing has brought new respect and a fresh look at yeast for carbonation. He explains that when technologies came into play where beer could be forcefully carbonated, that yeast continued to do what it does best, but took a back seat to producing bubbles.
“Except maybe in Belgium and in some odd recipes, people would rely on forced carbonation,” he says.
But he cites anecdotal evidences that more people are using just yeast to carbonate beers and in many cases, when done properly, naturally carbonated beer can produce just as much CO2 as a forced carbonated beer. If the beers use yeast over CO2 they tend to have a creamier flavor, White says.
Overall, White calls yeast “amazing” because it produces alcohol but “it has all these flavor compounds, we get something that tastes good and that carbonates as well, it’s pretty amazing.” (need to mention the flavors)
Forcing In The CO2
Once a year Graham, of More Beer, teaches a homebrewing course at the Siebel Institute in Chicago. Without fail, he says, the majority of questions at the end of the week focus on carbonation issues.
Recipes call for carbonation levels of various pressures and the equipment available to brewers today help to regulate the CO2 intake to make sure the gas is dissolved into beer. Also, CO2 works best when it is working with a beer below 60 degrees.
This can be accomplished with a CO2 tank and regulator where the carbon dioxide is slowly introduced to a keg, allowing the liquid to absorb the gas over time and achieve perfect serving carbonation. Carbonating slowly over the course of five to seven days not only gives the beer a chance to age, but also increases the likelihood that the beer will not over carbonate.
However, Graham says that more often than not beginning brewers will cheat a bit and “do double carbonation in half the time.” The problem is that unless you are constantly checking the beer along the way and able to know when it has reached the desired level by look and taste, you are likely to wind up with an overly carbonated beer.
Graham admitted to hedging his bets in the past, but says there is no proper substitute—in this method—to taking ones time. “In a way, you are screwed when you over carbonate. It will foam like crazy, and the only thing you can do is release pressure from a keg over the course of several days, tasting along the way. Still, there are no guarantees it will come out OK.”
