Rather than pitching a fresh pouch of yeast into every batch of beer, most professional breweries reuse yeast harvested from prior batches. And that practice is commonly replicated at the homebrew level. But how best to do it, and what are the limitations? Brülosophy contributor Jordan Folks has harvested yeast for reuse over one hundred times and he’s going to show us exactly how he does it. Plus we’re going to look at the results of an exBEERiment to see if blind tasters could tell the difference between a beer brewed with harvested yeast versus one brewed with a packet of fresh yeast.
4 thoughts on “The Brülosophy Show: How To HARVEST and REPITCH Yeast”
Thank you for this article. I have been re-using yeast for years. The problem with using a yeast slurry is all the hop particles, cold break material and dead yeast cells that it contains. Washing the yeast could introduce the risk of bacteria, and yeast washing only works effectively for ale yeasts which stay in suspension and settle near the top. Lager yeast settles almost immmediately, so is left in the bottom layer. Each time you harvest the slurry, the amount of trub increases.
For these reasons. I have developed a unique solution. When I get a fresh package of yeast, I immediately make a 3-liter starter. When done, I pour one liter in a one-liter Mason jar and pour the other two liters in a two-liter Mason jar. Then I put them in the refrigerator. When the yeast in the two liter Mason jar has settled after a few days, I pour off the liquid portion and use the settled yeast slurry directly in a brew. The other jar stays in the refrgerator until I’m ready for my next brew. Then I use that one liter of yeast to make another three liter starter (add yeast nutrient) and repeat the process.
In this way, the yeast stays fairly pure, with no accumulated hop particles, cold break material, etc. You can easily repeat this about eight or more times. I generally stop at eight generations but likely could use it more times, since the yeast remains fairly pure. I have noticed little change in the resultant beer – perhaps it even improves a little.
You can also easily bump this up to using the same yeast 14 times while keeping the yeast at no more than 8 generations! What I do is, for every time I brew a beer, I make another beer over the slurry of the previous beer. In this case, I would not use the slurry an additional time. Thus you would make two beers out of each two-liter Mason jar, so that by the seventh jar, you have made 14 beers, while the fairly pure yeast has only generated eight times.
To me, this is an inferior way of doing things. I overbuild every time because I don’t want to re-introduce cold break, dead yeast, and spent hops and grains. Also, if you reuse yeast, you stand the chance that there will be some carryover of flavors from the previous batch(es). If you keep brewing the same beer over and over, this will not be a factor. But if you do brew a strong dark lager and reuse that same yeast in a light pilsner, you may experience an undesirable flavor.
Plus, overbuilding is much more easily done. Also, the amount of yeast is measured much more accurately since dead yeast, cold break, spent hops and grains are not present in the overbuild. Just a much cleaner process resulting in a cleaner yeast.
Can this process be applied with dry yeast?
I do the same as John,ie. create a sort of “Scoby” similar to Ginger beer and Kombucha so as to keep the yeast base clean. And yes I rehydrate dry yeast always as I live far from wet yeast sources