Learn­ing Lab: Yeast

In this is­sue’s Learn­ing Lab col­umn, Jester Gold­man shows you how to ex­pand your knowl­edge of yeast strains so you can pick the right yeast for your next batch of home­brew.

Craft Beer & Brewing Magazine - - Contents -

IN THIS SERIES, WE’VE ex­plored hops and malt. Now it’s time to take a closer look at yeast. As a home­brewer, you’re prob­a­bly al­ready fa­mil­iar with the two main fam­i­lies of brew­ing yeasts, know­ing that mem­bers of Sac­cha­romyces cere­visiae (ale yeast) pre­fer warmer tem­per­a­tures and tend to fa­vor ester pro­duc­tion, while mem­bers of Sac­cha­romyces pas­to­ri­anus (lager yeast) tol­er­ate cooler fer­men­ta­tion tem­per­a­tures and are more likely to pro­duce sul­fur com­pounds such as dimethyl sul­fide (DMS). You’ve also faced the plethora of choices at your lo­cal home­brew shop.

At a finer grain of de­tail, yeast strains are of­ten char­ac­ter­ized based on their at­ten­u­a­tion, floc­cu­la­tion, and al­co­hol tol­er­ance. At­ten­u­a­tion (or “ap­par­ent at­ten­u­a­tion”) refers to the per­cent­age of wort sug­ars that the strain can process. Sweet wort is made up of many dif­fer­ent kinds of sugar, and some yeasts have trou­ble with the more com­plex ones. That af­fects the fi­nal grav­ity and resid­ual sweet­ness in your beer.

Floc­cu­la­tion is how well and how quickly the yeast cells set­tle out of the beer. Strains with high floc­cu­la­tion are likely less at­ten­u­a­tive and may yield beers with some level of but­tery/but­ter­scotch fla­vors when the yeast set­tles out with­out driv­ing off the nat­u­rally pro­duced di­acetyl.

Al­co­hol tol­er­ance is fairly straight­for­ward: It de­scribes how much al­co­hol a yeast strain can tol­er­ate be­fore it stops work­ing.

Be­yond those base char­ac­ter­is­tics, strains can also dif­fer by their propen­sity for gen­er­at­ing cer­tain no­tice­able fla­vor com­po­nents such as clove and other phe­nols, fruity es­ters, di­acetyl, and DMS. A yeast’s per­for­mance can be af­fected by pitch­ing rate, oxy­gena­tion, and fer­men­ta­tion tem­per­a­ture, but it helps if you un­der­stand the ba­sic char­ac­ter. That’s the knowl­edge you need to choose the right yeast for your next batch.

Pick Me!

Most of us start with a short­cut and just go by the name (e.g., we choose a Kölsch strain when we’re plan­ning a Kölsch). But if you’re brew­ing an ESB, there are sev­eral English/british ale yeasts to pick from, so you need to look a lit­tle deeper.

The next level is to read the de­scrip­tions and style ad­vice that the man­u­fac­turer of­fers. All of the main­stream yeast com­pa­nies pro­vide those ba­sic qual­i­ties (at­ten­u­a­tion, floc­cu­la­tion, al­co­hol tol­er­ance, and per­haps an ideal fer­men­ta­tion tem­per­a­ture range), along with gen­eral de­scrip­tions of the char­ac­ter. That’s quite use­ful, but it can still be chal­leng­ing to dif­fer­en­ti­ate strains. For ex­am­ple, White Labs WPL820 Oc­to­ber­fest/märzen Lager Yeast and their WLP920 Old Bavar­ian Lager Yeast are pretty sim­i­lar, with each fa­vor­ing malty lager styles.

Real-life sen­sory eval­u­a­tion is nec­es­sary to make those de­scrip­tions more real and to dig deeper into the nu­ances. We’ll get that ex­pe­ri­ence with an­other sim­ple ex­per­i­ment. This process will give you a more vis­ceral sense of all of those tech­ni­cal terms and the gen­er­al­iza­tions in the de­scrip­tions. “Ap­par­ent at­ten­u­a­tion” may be hard to con­nect with on the printed page, but the dif­fer­ence is easy to un­der­stand when you taste your sam­ples.

The Ex­per­i­ment

We could just shot­gun the avail­able yeast strains and con­trast a wildly di­ver­gent set, but it’s bet­ter to pick a tar­get beer style (in this case, pale ale) and choose re­lated strains of yeast. Here’s a list I came up with that’s pri­mar­ily fo­cused on Wyeast strains, along with a cou­ple of Safale choices:

▪ Wyeast 1056 Amer­i­can Ale

▪ Wyeast 1272 Amer­i­can Ale II

▪ Wyeast 1332 North­west Ale

▪ Wyeast 1217PC West Coast IPA

▪ Wyeast 1099 Whit­bread Ale

▪ Wyeast 1318 Lon­don Ale III

▪ Wyeast 1335 British Ale II

▪ Wyeast 1098 British Ale

▪ Fer­men­tis Safale S-04

▪ Fer­men­tis Safale US-05 This set con­trasts Amer­i­can and British strains, as well as liq­uid and dry yeast. An­other al­ter­na­tive would be to choose a mix of Wyeast and White Labs yeast strains to see whether equiv­a­lently named strains be­have the same.

As with any ex­per­i­ment, we want to re­duce the vari­ables and fo­cus on the yeast alone. We’ll use a sin­gle recipe to share across the set of yeast strains, and we’ll en­sure that all of them fer­ment at the same tem­per­a­ture.

Any style will do; you might want to pick a recipe you brew reg­u­larly. For our pur­poses, I’ve se­lected a ba­sic ex­tract pale-ale recipe that will pro­vide a sim­ple can­vas on which to com­pare yeasts (see “Base Paleale Recipe,” page 46).

Which­ever route you de­cide to take, fol­low the direc­tions to brew a full 5 gal­lons (19 liters) of wort up to the point where you chill the wort, but be­fore you pitch the yeast. From that point, we’ll take a sim­i­lar mini­batch ap­proach to our ear­lier learn­ing labs.

Af­ter chill­ing the wort, split the batch into ten 1-gal­lon (3.8-liter) glass jugs, fill­ing each one about halfway, so that you have ten 0.5-gal­lon (1.9 l) sam­ples, each of which will get its own yeast strain. (If you pre­fer a smaller field for com­par­i­son, you could split it five ways in­stead of ten). As you’re pitch­ing the ap­pro­pri­ate yeast in each con­tainer, use a full pack­age of liq­uid yeast or a half pack­age of dry yeast. Be sure to la­bel each sam­ple so you can eas­ily keep track.

Fer­ment all of the mini-batches at the same tem­per­a­ture (aim for about 68°F/20°C). Once fer­men­ta­tion is com­plete, bot­tle each mini-batch with about 0.4 oz (11 g) to­tal dis­solved prim­ing sugar.

Anal­y­sis

Af­ter a cou­ple of weeks in the bot­tle for car­bon­a­tion, it’s time for taste test­ing. Look over the yeast pro­files for your se­lec­tion of strains. Read through the de­scrip­tions, then put them in re­verse or­der by ap­par­ent at­ten­u­a­tion. While most of them should be fairly close, sam­pling from drier (higher at­ten­u­a­tion) to sweeter (lower at­ten­u­a­tion) re­duces the chance that the drier sam­ples will seem harsh.

Pour the first beer and take a good sniff. First, you should fo­cus on fer­men­ta­tion char­ac­ter: look for fruity smells or but­tery di­acetyl, maybe a hint of sul­fur. For the yeasts listed above, you’re un­likely to get phe­nols or DMS. With your sec­ond whiff, con­sider the malt and hops ex­pres­sion, as well as the bal­ance be­tween them. Write down your im­pres­sions, cap­tur­ing as much qual­i­ta­tive de­tail as pos­si­ble. Fol­low the same ap­proach for your first cou­ple of sips: es­ters and di­acetyl first, then the beer as a whole. In ad­di­tion, get a sense of the body and resid­ual sweet­ness. When you swal­low, how are the fin­ish and af­ter­taste? Is the fin­ish crisp and clean, soft and lin­ger­ing? Is the af­ter­taste clean or yeasty? At this point, you should also look at the beer and as­sess its clar­ity.

Now, pull it all to­gether to see how the pieces fit. Hazy or cloudy beers will of­ten have more yeast bite, or in milder cases, the fin­ish will be softer. Higher es­ters will also de­crease the crisp­ness of the fin­ish. Af­ter you’ve got a good sense of the beer, re­view the yeast pro­file again and see whether your sen­sory notes are in line.

As you move on through the series, you’ll get a bet­ter sense of how the strains dif­fer. In par­tic­u­lar, the bal­ance is likely to shift from hops char­ac­ter to malt as the ap­par­ent at­ten­u­a­tion drops. Once

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