This guide was written by The Homebrew Forum member, ‘Oblivious’. It’s a superbly simple ‘how to’ guide which tells you how to harvest yeast for brewing.
You can find the original thread here.

How to harvest yeast for brewing

This is my method of yeast harvesting, this was done for my last brew a Saison with WLP550

After racking the beer to the keg pour the remaining liquid, trub and yeast into a sterilized container. I find one around 2 liters to be a good size. Place the full container in the fridge for a few hours.

Harvesting yeast

The trub being heavier, will settle out faster than the live yeast. It is the liquid part we are interested in as this will have a greater concentration of viable yeast. Pour this liquid off into a new sterilized container, this can be of a smaller than the first and place in the fridge over night.

Reusing yeast

As the liquid we placed in the container is yeast rich, we want to harvest the sediment in this container. Decant of the majority of the liquid and transfer the rest includin the sediment to your storage vessel, I use sterilized 50ml tubes.

Yeast Sediment

Yeast harvesting

Decant off the majority of the liquid and pour the yeast in to your selected container. I find there is enough yeast  in each of these tubes to pitch into a starter for a month or so. Over that it I would add two of the tubes to a starter.

Yeast Vials