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

An airlock is a water-barrier that allows co2 to escape during fermentation, without allowing airborne particles, bacteria or insects to enter the fermentation vessel.

A U-bend Style Airlock

A blow-off tube replaces the airlock in a fermentation vessel. One end attaches to the top of the fermentation vessel and the other end is submersed in a container full of water.

A Blow-off Tube

Which one should I use?

For most brews, an airlock is fine. The advantage of an airlock is that it is relatively small compared to the blow-off tube, and is much easier to maintain. The problem with airlocks is that a very aggressive fermentation can clog the airlock with Krausen, causing a build up of pressure in the fermentation vessel. When that pressure gets too much, either the airlock or the lid of the fermentation vessel will pop off with great force, causing a big mess. A blow-off tube is much less likely to clog up than an airlock.

A Clogged Airlock

If you are brewing a beer using a top-fermenting yeast (most wheat-beers are brewed using this type of yeast), then you should always use a blow-off tube. This is because top-fermenting yeast produce a much higher, thicker krausen than regular ale yeasts and are much more likely to cause problems when using an airlock.

How to make a blow-off tube.

1. Attach a piece of sanitised tubing to the opening of your demijohn (or lid of your fermentation bucket) using a sanitised stopper with a hole in it.
2. Half-fill a small container such as a measuring jug or pint glass with water, and place the other end of the tube inside, below the level of the water. You do NOT need to use bleach or sanitising solution for this!

For an in-depth tutorial on how to build a blow-off tube, check out this article at examiner.com.

Thanks for reading,
Brewing-tips.com Staff