Till 1970, dry yeast was not used commercially for brewing. Most breweries would save a bit of the trub and use it for their next batch. Even bakers would mix a part of their old dough to leaven their new batch of bread. This practice has seen a comeback due to the resurgence of sourdough technique in baking.
Traditional Wine makers throughout Europe would cultivate the yeast biome. They would compost the lees and all the organic residue from the wine making process. This compost is used as a natural organic fertilizer for their fruits and grapes. In doing so the yeast strain that the particular unique natural strain of yeast (which is locally available and isolated) would dominate the biome. The fruits now just need to be juiced and they will start fermenting naturally.
Kveik yeast is also usually harvested and rarely cultured. Traditional households would make special oak rings or towers that they would insert in their brew. The yeast would attach themselves to the wood and this wood would be used to inoculate the next batch.
How to Harvest Liquid Yeast at Home
Today we are going to talk about how to harvest yeast from your old batch. Depending on which school of yeast harvesting you follow, you can either top-crop or bottom crop your yeast. If you are using a conical fermenter, then it comes with a free yeast harvesting attachment. Once you have harvested the yeast, you should wash it. Doing so will get it rid of all the hops and sediments which can lower
You can choose to use fresh liquid yeast by adding some yeast nutrient and making a starter culture. Post that you can:
Use the wet yeast as is. Keep feeding it every 3rd day with some fresh wort to keep it alive. Store it in the refrigerator dairy section (4 degrees) so that its metabolism is reduced. Best if you are planning to reuse the yeast within a month. Make slants using glycerine. This will allow you to freeze them and store for ~2years Dry the yeast. Especially Kveik. The home-dried yeast typically have a shelf life of 90-180 days.