Save the yeast!

My night-before-brew-day (Brew Day Eve?) ritual consists of a) weighing and grinding the grain for the mash, b) preparing the yeast slurry, if necessary, and c) setting out the first stage equipment. I mentioned the yeast preparation briefly in last week’s recipe, Mortal Sin, and promised to divulge my secrets for re-using and re-culturing yeast.

If you brew, you know that the right yeast strain can make the difference between a good beer and a great one. There are, in fact, certain beers that cannot be brewed without the correct yeast. Anchor Steam depends on a very specific warm-tolerant lager yeast; Belgian Trappist beers would just not work without a traditional high-alcohol tolerant strain; in trying to clone Dieu Du Ciel’s Mortal Sin last week, we went to great pains to capture and reuse the yeast found in their bottles.

The other thing about “the right yeast” is that it can get expensive. Fresh liquid yeast costs anywhere from $5 to $8 in the home brew shop. But if you can save it, re-use it, you cut the cost down. Tomorrow I will be brewing a Munich Dunkel lager, using the same Southern German Lager yeast from White Labs that I used to brew my delicious Munich Hell, Vienna Lager, Bock and Rauchbock over the last few months. Yup, using the same yeast, for the fifth time. Here’s how I do it. Caution: some purists, some much more scientific types, will cringe, shudder and scream at the computer screen as they read this. I know, this shouldn’t work this easily. But it does, it has, and I have no qualms about sharing my dirty little secret.

Yeast in Sanitized Milk Bottle
Yeast in Sanitized Milk Bottle

It starts on the day I rack a beer from primary to secondary. If the beer to be racked was brewed with a yeast I know I am planning to reuse soonish (within the next couple months, generally), and if the initial fermentation has gone well, as far as I can tell, I sanitize a glass pint-sized milk bottle. After racking the beer into the carboy, I scoop out, with a sanitized measuring cup, a cup or so of the dregs. These dregs consist of malt proteins, hop debris, and hopefully a fair amount of yeast cells. These dregs are poured carefully into the pint bottle, a solid rubber stopper is affixed, and the sample goes into the fridge.

Close up of Yeast
Close up of Yeast

A day or two before I will be brewing with the saved yeast, I sanitize a glass quart-sized milk bottle. I boil a cup of water with two tablespoons of dry malt extract for about 5 minutes. This wort is cooled to 70 – 75°F, poured into the sanitized quart bottle, and the saved yeast dregs are poured carefully into the cool wort. A little swirling to mix, and a stopper with an airlock is put on the bottle. I let it work for 12 hours or so, and if brewing is still a ways off I might “feed” the yeast again with another 1/2 cup of water boiled with 1 tablespoon of DME, chilled of course. Voilà, on Brew Day I have a cup and a half or two cups of active yeast slurry, ready to pitch.

In the case of a commercial yeast captured from a bottle, this process takes place a little at a time over several days, with a gradual slow build-up of a quarter to a half-cup at a time.

So, my Southern German Lager yeast is just beginning to foam and bubble, two hours after pitching, and should be ready to pitch in my Munich Dunkel in about 13 hours. See you then!

4 Replies to “Save the yeast!”

    1. Think of it as similar to a sourdough sponge – you use a part of it, but feed and save the rest for the next batch… If you only bake with dry yeast, it would be hard to reculture anything after the bread is done. But, many cultural anthropologists suggest that the whole reason for making bread in the first place was to save the yeast for brewing… Several Eastern European brews, including Russian Kvass and Finnish Sahti are made with baker’s yeast, and in fact are often started from a partially-baked loaf of rye bread. Thanks for your comment!
      -The Guru

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