Saturday, August 27, 2011

Yeast: Bottle Harvesting

Bottle Harvesting: the process of bringing nearly dead yeast back from the dead. Yeast Frankenstein, if you like.

Maybe you want to brew a spot-on clone but they don't sell that particular brewery's yeast strain. Maybe you're cheap and want 'free yeast'. Or maybe you're just a homebrewer, and you don't need a goddamn reason. Here's how.

 First off, some resources. Jamil Zainasheff discusses yeast propagation from bottles on page 208-209 of his book yeast. John Palmer discusses it in his book How to Brew (link to 1st edition here). Papazian's The Complete Joy of Homebrewing covers yeast culturing in general on page 265, and most of the information applies (like everything else in that book, info tends to be outdated). The internet has plenty of information as well. As with any homebrewing info you find via google (especially anything on, take it with a grain of salt. Homebrewers can be very dogmatic. Though I try my best, that includes me.

The first thing you need to know is that yeast harvesting can be hit or miss. The pressures of alcohol, heat and time will kill off tons of the yeast in the bottle. Yeast can also mutate over time, leading to a culture that isn't quite the same as the one the brewery uses. To ameliorate these problems, go for a fresh bottle (check the freshness date, if there is one) of a lower gravity ale. Sometimes you can see the yeast plug. All else being equal, get a bottle with a fat, bright white, solid chunk of yeast. Yeast that is discolored, flaky or chunky compared to the same yeast in other bottles probably isn't the healthiest. Buy two bottles, preferably 22 oz bombers. I'm sure you can manage to drink that much.

It goes without saying that the beer must be unfiltered and/or bottle conditioned. However, one thing to remember is that some beers are bottle conditioned with either a different yeast strain than the one used for fermentation or are filtered and conditioned with a small addition of the same yeast. Many traditional hefeweizen brewers do the former, using hefeweizen yeast in the primary and bottle conditioning with a lager yeast. Sierra Nevada does the latter, and there is typically barely enough yeast left in the bottle to harvest. You can get WLP001 or 1056 anywhere, so it isn't worth the trouble - buy one vial and repitch your own slurry (or wash it) for several generations if you want to save money.

Once you've done your research, you should now have an unfiltered, low to mid gravity beer from the brewery whose beer you want to replicate. Chimay and other trappist beers are a popular choice, as is Rogue's Pac-Man yeast (wakka wakka wakka wakka). Unusual Belgian strains and sour cultures are also good candidates, because they can be hard or impossible to find in a vial.

I picked up some Rogue Shakespeare Stout and Chocolate Stout with no intention of bottle harvesting. When I saw the big, fat plug of yeast in the bottom, I couldn't resist. Rogue's yeast can be difficult to find - it is only sold by Wyeast, and even then it is a seasonal offering. I can't find it locally. It is related to the typical California Ale yeast, but is widely considered to attenuate and flocculate better, and has a slightly different character. It's called "Pacman" because it just gobbles everything up!

Here's what I did, step by step:
  • Refrigerate the beer. Don't let it sit on its side. You want to make sure as much yeast has dropped out as possible.
  • Prepare a very small starter. I used 20 grams of light DME and some yeast nutrient in 200 mL water. Boil it and cool it in a sanitized glass container, just as you would do with any starter. If you don't do starters, why are you reading this?
  • Pop the top. Sanitize the bottle and rim however you like - I sprayed it with star san solution out of a squirt bottle and then flamed the bottle opening with a lighter.
  • Pour the beer into a glass, carefully (no glug glug action!!!) until there is only around an inch of beer left in the bottle. Don't pour any yeast into your glass.
  • Swirl the remaining beer as hard as you can to get it dislodged from the bottle and in solution. Dump the yeast/beer mix into your starter. Oxygenate and grow as you usually would. I used the Shakespeare Stout.
  • After a day, your small starter should have fermented out. Create more wort to step it up to half a liter. I added another 30 grams of DME, some yeast nutrient and 300 mL of water, boiled and cooled, straight into the jar. Add the yeast from your second bottle, especially if you didn't get much activity in the first attempt. I got virtually no activity on the first try, so I added the yeast from the Chocolate Stout, which seemed to have more yeast sediment than the Shakespeare.
  • After another day, step it up to a liter. I added another 50 grams of DME, yeast nutrient and 500 mL of water. My yeast finally took off after adding the yeast from the Chocolate Stout. You now have a 1 liter starter that you can use however you want, or even step up to 2 liters. I prefer to refrigerate my starter to decant the starter beer off the top, but you will have a faster start to your fermentation if you dump it all in while active.
And that's it. It's way easier than it seems. If you've made a starter before, this is a piece of cake. I plan to make the CYBI Rogue Dead Guy clone, just because I can!

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