Today I put my Heavy Seas Gold Ale clone into bottles. I ran out of bottles before I ran out of beer, so I put the leftover into a growler and chilled it to accompany our dinner. Colleen and I are both looking forward to it maturing over the next three weeks — it’s a promising brew at this stage. After I was finished bottling, I decided to give the yeast a bath to clean them up after their boozy party.
Yeast washing is a procedure for recovering the yeast from your brew so that it can be reused in future brews. The idea is to repeatedly swish up the yeast and trub in pre-boiled water (which both sanitizes the water and purges it of oxygen), letting them settle into separate layers, and then pouring off the yeast and water from the proteins and hops in the trub. Most guides out there recommend two iterations: letting the slurry sediment once in the fermenter, and then letting it sediment again in a jar, before finally transferring it to the jar it will be refrigerated (not frozen) in. While some homebrewing experts advise that washed yeast be used within 2 weeks, many homebrewers tell of reviving yeast as much as 6 months later.
I boiled my jars for 15 minutes, sealed them, and put them in the fridge until they reached room temperature. I then sanitized a funnel, and added the water from the jars to the fermenter. After giving the fermenter a good swirling, I let it sit for half an hour. Supposedly one should be able to identify a layer of yeast sitting atop a layer of trub once the particulates have sedimented from suspension. The yeast should be slightly lighter in color than the trub. The slurry from the fermenter is poured off into the largest jar, taking care to leave the darker layer of trub behind as much as possible while pouring off all the yeast.
My slurry showed no such stratification. Nonetheless I forged ahead, pouring off a decent amount of trub into one of the mason jars just to be sure I got at least some yeast. There is of course still plenty of yeast in suspension in the liquid part of the slurry, but since I would be letting the slurry sediment again, I figured there was no harm in pouring in some trub.
After another half hour had passed and the slurry had sedimented again, I poured off the liquid and part of the sediment (until I thought it started to darken) into yet another mason jar. I then put that jar in the fridge and refilled the mason jar I’d just emptied with slurry from the fermenter. It was around this time I took to the internet for a little more research about yeast washing and why I might not be seeing stratification.
It turns out that a rather terrific scientifically-minded blogger, Steven Deeds, has conducted experiments on yeast viability and population density in the strata that form during yeast washing. He found that the ratio of yeast to non-yeast particulates is roughly constant throughout the slurry obtained during washing, so all the pouring off and sedimenting is for naught. Additionally viability of yeast is not appreciably improved by washing.
He further found that yeast washing can actually be detrimental, due to the fact that bacteria populations are higher in the upper strata of the slurry, and so by discarding what is commonly supposed to be trub at the bottom of the slurry, one is actually selecting yeast that is more contaminated with bacteria (and possibly also selecting the least flocculent yeast). Therefore he recommends simply stirring up the slurry in the fermenter and saving it in its entirety in jars. The yeasty yield will be an order of magnitude greater and take less care and effort. Given my experience today, I think that is what I shall be doing in the future from here on out.
I’ll be using some of this yeast on Tuesday for my next brew, and hopefully also employ it in some baking to see how fresh brewer’s yeast stacks up against dried baker’s yeast.