Back To Basics: Yeast

I understand that my first few posts are a bit random and not a great place to start if learning about brewing, so I am going to dial it back a bit and talk about yeast.

Yeast is a relatively new ingredient in the brewing process. I'll let that sink in for a second. For thousands of years yeast wasn't something that brewers put into their beer. The original German beer purity law, Reinheitsgebot, only allows brewers to put malt and hops in water to make beer. This changed in the mid to late 1800s when yeast was discovered by Louis Pasteur. 

Yeast is a naturally occurring microorganism that is present as "wild strains" all over the world. Over the past 150 years brewers have mutated strains of yeast to impart different qualities to their beers. Homebrewers now can boil off any wild strains of yeast that are present in their grains, and populate their wort with only the specific strain that they want the characteristics of.


Commercial breweries could give you their exact recipe, but without their exact proprietary strain of yeast you would only be able to get close to their beer's taste. These breweries employ entire biology departments to ensure that the yeast strain doesn't mutate. If something bad does happen, more of their yeast is sitting in a high security vault ready to save the day. Yeast to these breweries are on the same level of importance as seasonings are to KFC, and Coca-Cola Classic's recipe is to Coke. 


Below are some of the more common terminology that is used when talking about yeast: 

• Pitching - Putting yeast into the wort.
• Types - Top fermenting, also know as ale yeast ferments at the top of the wort at higher temperatures. This yeast ferments quicker, and can impart more esters on the beer. Bottom fermenting, also known as lager yeast ferments at the bottom of the wort at lower temperatures. This yeast ferments slower, and gives beer a crisper, cleaner taste.
• Strains - The strain of the yeast is a sub-category of the type. There are an unlimited number of strains of yeast, because any minor mutation results in a new strain. 
• Attenuation - Sparing you the math involved for now, attenuation is the percentage of the malt sugars that are converted into alcohol during the fermenting process.
• Flocculation - Flocculation is a term that relates to how well the yeast settles to the bottom of the fermenter after fermentation is complete.
• Lag Time - Lag time refers to the speed at which the yeast, after being pitched, has depleted the oxygen in the wort during the reproduction process, and starts to turn sugars into alcohol and CO2.
• Esters - Esters are the flavors that the yeast give to the beer during the fermenting process.