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Cutline: An Erlenmeyer flask of sterile wort ready for inoculation with yeast. (Contributed photo by Rick Oftel.)

Most of the snow is gone so it’s time to brew spring beer. I can brew in the winter but the brewery requires too much energy to keep the yeast happy.  Happy yeast makes great beer so keeping them in the dark (they like dark) and at the right temperature ensures good beer. 

People brew bitter wort, and yeast converts wort into beer. Yeast are a fungi that were unknown at one time except for their actions. They live by decomposing and absorbing organic matter and produce ethanol. As science progressed, Louis Pasteur proved this and created a laboratory process to isolate and grow a single fungus into a thriving colony capable of fermenting a batch of beer or wine.

There are two primary types of yeast, lager and ale.  Lager yeast was at one time called “bottom yeast” and is used for slower fermentation. It requires cool fermentation temperatures and the finished beer has limited yeast flavor. Lager is German for “to store,” so lager beer was stored cold for long periods. With enough time, lager yeast usually drops brilliantly clear, although commercial breweries “cold filter” to speed up the process and artificially clarify. 

Ale yeast was at one time called “top yeast” as it floats above and coats the bitter wort with a dense cover. A famous brewery in England used a series of tanks and troughs to slowly move the wort through the brewery. The floating yeast cover was so thick that it protected the beer on the journey. Ale yeast ferments best around 65 degrees and at warmer temperatures, it adds interesting flavors to the finished beer.    

Two important yeast terms include attenuation and flocculation. Attenuation is the relative degree of fermentation. Highly attenuative yeasts consume slightly more sugar and leave a little less body and mouthfeel. Flocculation describes how well the finished yeast clumps together and drops out of suspension or clears. My favorite culture is a simple strain from Chico, Calif., used commercially in Sierra Nevada Pale Ale. The yeast works hard, consumes most of the sugar, and drops very clear. 

The yeast industry is willing to culture, grow, and sell a huge variety of liquid and dry yeast to match any requirement, and more than 70 strains are available to amateur brewers. I prefer using expanding smack packs because you can activate them and gauge the health of the yeast by the speed of swelling.

Most yeast packs contain adequate population to create five gallons of beer; a larger batch requires an interim step often called a starter. A starter is a small batch of beer inoculated with yeast. Yeast reproduce quickly so in about 24 hours, your starter is ready to inoculate the bitter wort. Larger breweries use multiple “steps” to grow cultures into usable populations.    

Growing cultures is simple and requires good sanitation. Boil three liters of water and 300 grams of dry malt extract. Pour into a clean and steam-sanitized Erlenmeyer flask. Cover the opening with boiled aluminum foil and cool in an ice bath to room temperature. When cool, sanitize the yeast pack and scissors. Shake the pack, cut the corner, and pour into the flask. Cover with sanitized foil or an airlock and wait for up to a day. At the correct temperature, this culture should be ready to work in 12-24 hours. Some brewers pour off a portion of the liquid before swirling and inoculating the bitter wort.

A magnetic stir plate speeds up yeast growth. Yeast reproduce by budding so a mixing system may increase yeast cell count. Besides, it’s always fun to tinker with equipment.

If you are fortunate enough to align your brew day with the emptying of a primary fermenter and you like that yeast strain, you can pitch your bitter wort onto the dregs of a recently emptied carboy.  Although it doesn’t look great, fermentation may begin in under one hour. On brew day, rack a batch of beer into a secondary fermenter and seal. When finished with the new batch, thoroughly cool and add the bitter wort into the recently emptied (dirty) fermenter.  A “peel-and-stick” thermometer is a good tool to monitor carboy temperature during fermentation as rapid fermentation produces heat.  Submerge the fermenter in cool water if the temperature climbs too high.

A homebrewer and beer judge with 25 years of experience, Rick Oftel escaped the Twin Cities and moved to a Bayfield house with a detached workshop. A sealed area holds the brewery used for beer, mead, maple syrup and for coffee roasting.    

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