Yeast is such a critical element in brewing, it makes sense to buy the best you can possibly afford. Once you’ve shelled out on decent yeast, it makes good sense to stretch your investment out as much as possible and reuse yeast for a few batches.
Every brewer knows the disappointment of pitching a bad batch of yeast (or for that matter underpitching or pitching too hot), so I’ve set out the steps below to help you get the best out of reusing yeast, without contaminating it.
WARNING – whilst the steps below help reduce contamination, and reusing yeast is fine for a few batches, each time you do this, your yeast will suffer… so only repeat this process once or twice for any given yeast strain. You can always harvest enough yeast to store in a few refrigerated, sterile containers and use these in several batches of beer.
It’s worth stating here that the harvesting to reuse yeast needs to be done when your brew is producing a lovely yeast head – well into the fermentation process. This will provide enough live yeast to skim off, without affecting your brew.
Step 1
Boil some water (filtered ideally) and leave to cool in a sterilised bottle (only 1/3 fill the bottle). Take care with boiling water (obviously!) and cooling it in glass containers… I’ve cracked a few in my time and that’s a bit scary.
Step 2
Sterilise a scoop and funnel. Place the funnel in the aforementioned bottle.
Step 3
Take the scoop to the yeast head and scoop a load of yeast.
Step 4
Dump the yeast from the scoop into the top of the funnel. It’ll drop down slowly into the water below.
Step 5
Repeat the process until you’ve gathered a few scoops – allowing each one to sink down into the water. The water causes the yeast to run out of food (wort) and become inactive. It’s stable like this for a month or two in the fridge.
Step 6
Cap the bottle and place in the fridge for your next brew.
You can cleanse the trub from the yeast if it looks a little messy. It’s best to do this by swilling up the yeast and water mix, then transfer this to another bottle after 30 seconds or so. This will have allowed the chunkier trub to drop out of the yeast. It’s not something I typically bother with, but I know people who like to take this extra step just to be extra sure it’s as clean as possible.
So there you have it – 6 simple steps to harvest and reuse your own yeast. Don’t get carried away to repeat the process too many times, but it’s easy to make a purchase of yeast last for 5 or 6 batches if you harvest enough. Good luck and happy brewing!