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Making the Yeast Happy
Quality beer starts with quality brewing, which proceeds through stages including malting, mashing, lautering, fermenting, conditioning, and filtering. Like any kind of cooking process, careful attention is required at each stage to ensure consistency and quality in the finished product.
The fermenting stage is one of the most important components, and, according to brewing quality consultant Alastair Pringle, of Pringle-Scott LLC in St. Louis, one that is often underemphasized.
“Some people don’t understand that yeast is a living organism that you need to treat right, just like you need to treat your tomato plant right if you expect it to grow,” he says.
The brewer must ensure that the wort—the liquid extracted from malt in the mashing process—has the nutritional qualities that the yeast wants, and that it has “the right balance of fermentable and nonfermentable carbohydrates to produce the right balance between alcohol and sweetness from unfermentable sugars,” Pringle explains. “Focus on the components of the wort, and then making sure that you treat the yeast right, that you pitch it at the right amount into the wort, and that you get the right amount of oxygen in there for growth. The single most important thing is to get the right amount of oxygen.”
When these elements are combined in the right quantities, he says, “the fermentation becomes predictable, and so does the quality of the beer, in that it tastes the same and analytically it’s the same.”
Once this stage is past, where oxygen is essential to yeast reproduction, further oxygen intake must be minimized.
“Zero would be the goal,” Harpoon’s Schier says. “Any exposure to oxygen after the beer has fermented will shorten its shelf life and remove the gustatory enjoyment of the beer, make it smell sweet and flat and flabby. Brewers work really hard to keep their oxygen exposure down, and a dissolved oxygen meter is an incredibly valuable piece of equipment to help with that.”
Keeping the living yeast healthy is vital for flavor production, Schier notes, as the yeast imparts a large percentage of the aroma and flavor present in the finished product. Producing the high-alcohol-content beers common in craft brewing can be stressful for yeast.
“In addition to ethanol, which is a form of alcohol, and carbon dioxide, which is the fizz in beer, yeast also produces a wide range of secondary metabolites, and they give to beer a big part of its flavor. Healthy yeast will produce those secondary metabolites in consistent and pleasant ratios. Yeast that is stressed out or unhappy will produce those metabolites in ratios that are inconsistent so that you don’t get the same beer time after time, or unpleasant combinations that just don’t work that well,” Schier says.
Sanitation is Key
The craft beer industry is fortunate, from a safety standpoint, that no pathogens can survive in beer with normal alcohol content, bitterness, carbonation, and pH. From a quality standpoint, however, brewers must be constantly on the lookout for what Kuhr, of F.X. Matt, calls spoilage organisms, “which would make beer not taste good but would not make it harmful. It doesn’t take much of a lapse of process to allow those sorts of bacteria to get a foothold, and then they will quickly have a negative impact on flavor.”
So essential is sanitation, he says, that “most brewers spend their first several months of their career just learning to clean, before they are ever trusted with brewing.”
Fraser concurs: “Craft brewers take sanitation and microbiology very seriously. There’s a lot of manual cleaning on the craft side, whereas the bigger breweries are more automated.”