One of the benefits of fermenting in a conical fermentor is the ease of yeast harvesting. I’m just starting to get into this. Up until now, I’ve used a different yeast strain for nearly every beer… and there’s not much point of harvesting yeast if you’re not going to end up using it again. So, an ongoing challenge of mine has been to refine the number of yeasts strains I use in my brewing. This is more difficult than I’d imagined, so, for now, I’m attempting to brew beers back to back that work well with the same strain. Most recently this has been a schwarzbier, followed by a helles, both using White Lab’s Southern German Lager strain – WLP838.
My process so far has been to perform a yeast dump into a sanitized 5L flask, then divide several litres of yeast slurry into sanitized pint jars. Eventually I’d like to incorporate an acid washing step, but I’m not there yet. Anyways, the pint jars full of slurry are sealed and placed at the back of the fridge until I’m ready to use them. I’d also like freeze (at least some of) my yeast instead of refrigerate for long term storage, but I’m also not quite there yet.
There’s a lot of yeast in these slurries; about 1 billion per millilitre of yeast cake. For me, this ends up being approximately 150 billion cells per pint jar. So as you can see it’s quite easy to harvest enough slurry such that a yeast starter isn’t necessary.
In refrigerated yeast cultures you can expect a loss in yeast cell viability and vitality. The loss of viability is irreversible, and estimated to be 25% per month. Vitality however is more dynamic and may be influenced through the environment of the yeast…
In walks the “vitality starter method”, brought to the attention to many of us homebrewers by the Brülosophy folks. It seems natural to utilize this method in combination with harvesting and storing yeast slurries to ensure a healthy, active fermentation. So… that’s what I’m experimenting with. It’s a bit early for me to comment on the effectiveness, however, I have found the process to be quite simple. I can prepare the vitality starter during the early stages of the boil without much trouble.