These days, when it comes to beer ingredients, homebrewers face an embarrassment of riches. Homebrew shops carry base and specialty malts from all over the world and numerous varieties of hops, including varieties not heard of just a couple years ago. And when it comes to yeast, homebrewers have an astounding variety to choose from.
Over 100 yeast strains are available to homebrewers for brewing ales, lagers, wheat beers, Belgian beers and even “wild” beers fermented with wild yeast and bacteria. Want to brew a British ale? You have about 40 yeast strains to choose from. How about a German lager? For that, you have over 20 choices. A Bavarian wheat beer with the aroma of bananas and cloves? There are 8 strains. What about a funky Belgian beer? A dry Irish stout? A huge, full-bodied Scottish ale? A clean American-style hop monster? A Kölsch or alt? A mouth-puckering sour beer? Your local homebrew shop has the yeast you need to brew all these styles and more.
To keep you up to date on what’s available, Brew Your Own presents our list of every yeast strain available to homebrewers on pages 32 through 34. And, we’ve thrown in two articles on how dried and liquid yeast are produced. (See pages 31 and 35.)
For each strain in the table, the level of flocculation is given. Strains are rated either high, medium or low depending on how quickly they drop out of solution following fermentation. Under proper brewing conditions, highly flocculant strains make beer that falls clear very soon after fermentation is over. With a less flocculant strain, you would have to wait longer for the beer to clear (or cool it down to coax the yeast drop out of solution).
The level of apparent attenuation for each strain is also given. Apparent attenuation is a measure of what proportion of the wort’s malt sugars the yeast consume. It is calculated by subtracting the final gravity from the starting gravity and dividing this result by the starting gravity. For example, if you made an OG 1.048 ale and it finished at a gravity of 1.012, the apparent attenuation would be 75% [(48-12)/48 = 0.75].
To achieve the levels of attenuation quoted here, you need to pitch an adequate amount of yeast, aerate your wort well and ferment the yeast within its proper temperature range.
The optimal temperature range for each strain is also listed. Below the stated temperature range, your fermentation may be sluggish, the yeast’s desired characteristics may be muted or absent or the yeast may not ferment at all. All yeast strains will grow happily above their optimal beer-making range, but they may produce a beer that is too fruity or contains higher alcohols (also called fusel oils).
Examining these numbers, and the brief description of each yeast’s characteristics (all given by the manufacturers) will help you pick the right yeast for your brew.
Dried Yeast, Past and Present
In the beginning, there was dried yeast . . . and it wasn’t very good.
In the early days of modern homebrewing, homebrewing for most brewers meant buying a can of malt extract with a packet of dried yeast in the lid. The yeast was sprinkled on top of the wort and left to do its thing. Since the yeast wasn’t dated, there was no way of knowing how old it was and sometimes fermentations didn’t start — and when they did start, the results weren’t always good.
Once liquid yeast came along, most homebrewers switched. There were many new strains to try and — rightly or wrongly — dried yeast gained the reputation of having levels of contamination high enough to cause problems, or at least concern.
Recently, though, things have changed. The technology for making dried beer yeast has improved, new dried beer yeast strains are available and many homebrewers are giving dried yeast a try and having good results. (Most homebrewers also realize that part of the blame for bad results in the “good ‘ol days” lay with stale extract and ill-considered brewing techniques.)
Commercial brewers are also experimenting with dried yeast. Hoptown Brewing in Pleasanton, California even won a gold medal at the Great American Beer Festival (GABF) for their IPA brewed with dried yeast (the Fermentis US-56 strain of ale yeast).
Compared to liquid yeast, dried yeast has its advantages and disadvantages. The advantages are that it costs less, stores longer and you can simply rehydrate the yeast when you brew — no need to make a yeast starter. And, if you want to up your pitching rate, you can just buy a second sachet of yeast.
The disadvantages of dried yeast are that there are far fewer strains available and, unlike with liquid yeasts, dried yeasts can carry a small load of contaminating microorganisms, which concerns some homebrewers.
Making Dried Yeast
I spoke with Bruce Patterson of the Lesaffre Group (producers of Fermentis dried yeast) about how dried yeast is manufactured.
Fermentis yeast strains are stored in a laboratory either at -80 °C (-112 °F) in glycerol or at 4 °C (39 °F) on slants. Each strain is genetically identified before it is sent to the factory for a production run. The yeast is transferred to a liquid media made from molasses (with a sucrose content of 45–55%) with added nutrients to supply nitrogen, phosphorous, vitamins and minerals. The culture is stepped up several times in the lab before being sent to the factory.
At the yeast plant, the culture enters a rapid cell production phase and the yeast are fed continuously with molasses, nutrients and oxygen. The yeast are grown in very large fermenters, much larger than at liquid yeast plants. (How big exactly is a trade secret.)
Next, the rate of cell division is slowed and, in preparation for drying, nutrients and unspecified agents are added to the yeast to help it survive the process. The yeast cells are then harvested, separated from their media and dried to a cream with between 15 and 20% solids. The cream is pressed into a cake and extruded through a mold to produce yeast “noodles.” The noodles are then dried in an air lift dryer.
In an air lift, the yeast sit on a grate and hot air is forced up through the yeast “noodles.” The yeast are churned sort of like corn kernels in a hot air popper. (An older way of drying the yeast is to put the yeast in trays and have it ride on a conveyer belt through a long oven.) The yeast are slowly dried until they contain 94% solids. The dried yeast is then vacuum packed into sachets, which have a shelf life of two years when stored under 10 °C (50 °F). The viability of the dried yeast is 86%, but each dried yeast packet contains about 10 billion living cells per gram. Thus an 11 g pouch would contain about 110 billion cells. (These are the numbers for Fermentis yeast. The numbers for Danstar Nottingham and Windsor yeasts are comparable.)
Dried yeast companies report a very low contamination rate. (Fermentis yeast, for example, reports less than 5 bacterial cells/mL of wort in adequately pitched wort.) Patterson, however, mentions that sometimes the level falls below what can be detected in the lab. And, the experience of many brewers shows that this level does not result in problematic beer.
Chris Colby would like to thank Bruce Patterson of Fermentis for his help.