Monday, May 21, 2012

Yeast Starter

Making a yeast starter is a necessary skill for someone who wants to brew beer. A yeast starter takes either a small quantity of yeast and grows it to the volume needed to ferment a batch of beer or takes a culture of yeast that is not healthy enough to brew a batch of beer and produces new cells that will be able to ferment the beer, or both.

In order to create a yeast starter you will need a few basic things...
  1. Dry Malt Extract
  2. A sterile vessel 
  3. Tinfoil
  4. A stir plate (not essential)
  5. Yeast
  6. A sterile toothpick of inoculation loop
  7. Scale
  1. The first step is to make a wort that is about 1.040 gravity. This is easy to do using Dry Malt Extract, simply add 1 oz of Dry Malt Extract for every cup of water. 
  2.  Boil the wort to sanitize it
  3. Sanitize the inoculation loop and whatever you will be growing the yeast in
  4. Add the wort to the vessel and place tinfoil over the top, allow the wort to cool to 80 F
  5. Add the yeast, using sterile practices, to the wort (you will only need a very small amount of yeast, a few colonies will do)
    1. If you have a packet from Wyeast or a tube from White Labs you can add the whole tube 
  6. If you have a stir plate available to you you can place the vessel on the stir plate in order to promote propagation. If you do not you should pick up and swirl the vessel as often as you can in order to keep it oxygenated.

The only tough decision is how much of a starter to make. If you are using a tube or packet from a commercial yeast producer you probably want to use a quart of wort. If you are picking single colonies you will only need 2 cups of starter (that you can then step up to a quart if you would like). I like to place my starters in the fridge after they have grown for 2 days in order to make the yeast fall to the bottom. I can then pour off the majority of the liquid and add only the yeast to the beer. A starter is good for a week in the fridge before you need to think about starting over.

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