In an attempt to make my brewing more efficient, continuous and economical I’ve been investigating how to harvest yeast from bottles. Here I explain how to do it.
Benefits of Harvesting Yeast From Bottles
There are several reasons to harvest yeast; perhaps to save money or to use a commercial brewery’s yeast in your home brew.
In general, when reusing your own yeast it’s better to take it straight from the fermenter, because that doesn’t necessarily require a yeast starter.
Harvesting from bottles is mainly useful if you forget to do that, or if you want to resurrect a special yeast from a particular beer. I’m planning to harvest some Belgian yeast later in the year, for example.
The technique works best with medium or weak beers, because high alcohol levels can damage yeast.
How To Do It
- bottle conditioned beer
- malt or malt extract
- container for yeast (a 2 litre plastic bottle will do)
The yeast in a typical bottle of beer are dormant and small in number. You need to wake them up and encourage them to multiply.
To do this you prepare a yeast starter, which is essentially a mini- batch of home brew.
One approach is to boil dry malt extract in water but if, like me, you enjoy the brew process in itself, you can carry out a mini-mash instead.
To begin, heat 1 litre of water to 63°C in a small pan and add 200g base malt.
Try to use a malt that’s similar to the ingredients in your planned recipe. For example, use pale ale malt if you’re going to use the yeast in a bitter.
After mashing (I leave it for one hour) remove the grains and drain, and bring the wort to the boil.
Boiling sterilises the wort so that you can add yeast without fear of infection.
After twenty minutes remove from the heat and put the pan in cold water to cool.
While that’s happening, prepare the starter jar. I use a simple plastic bottle but any 1 – 2 litre, clean container is fine.
It’s essential to sanitise effectively for your yeast to have any chance of survival. Star San is effective.
Now’s a good time to check your beer is to hand.
In their great book Yeast, Chris White and Jamil Zainasheff recommend storing the beer for a week before you need it.
This encourages the yeast to settle out of the beer and form a compact layer on the bottom of the bottle.
When the wort is cool carefully pour it into the sanitised bottle.
The foam in the photo is from the Star San. You could use a funnel to make pouring easier, but I don’t.
Although the foam looks alarming, according to the Star San manufacturers this is harmless and can actually provide nutrients to the yeast.
Open the beer. Immediately (before pouring) sanitise the neck and opening. A spray bottle is useful.
Pour the beer into a glass for drinking, leaving the yeast sediment and a little beer in the bottle. Swirl it up and tip it into the yeast starter.
Give it a good shake (with the lid on).
Remove the lid and lightly cover with film. If your fermenter airlock fits use that instead. Gas should be able to escape without letting air and bacteria in.
Leave the starter undisturbed to ferment.
Because it’s such a small amount it should happen quickly.
You’ll see a krausen layer build on top and then gradually die down.
The whole fermentation process takes around two days, plus a day for settling, so you should harvest the yeast about three days before you plan to brew.
John Palmer suggests putting the starter in the fridge the day before brewing so the yeast settle to the bottom. Depending on how tasty your starter wort is, you may want to pour it away and pitch the yeast alone into the beer, or just add everything.
With this batch I removed most of the starter, pitching just the yeasty slurry that was left.
The yeast will keep for a few days but after that it may need reinvigorating again with more starter.
You can keep harvesting forever, but most advice suggests that after 6 or so times it’s worth starting again.
This is an easy (and weirdly satisfying) brewing technique – give it a try.