Preparing a Yeast Starter

A strong, healthy fermentation is the key to good beer (assuming the rest of the process went smoothly). Commercial brewers aim for a pitching rate of at least 200 billion yeast cells for every 5 gallons of wort. By contrast, the pitchable liquid yeast used by homebrewers provides roughly 30-60 billion yeast cells. Homebrewers who regularly prepare yeast starters swear by them as being the key to better beer. At some point in your brewing career, you will need or want to create a yeast starter. Yeast starters are acceptable for any batch of beer, but they are especially recommended for certain situations:

  • When brewing beers with an original gravity over 1.070, yeast starters are a must. High gravity beers really put yeast to the test, so preparing a yeast starter will ensure a strong start and a healthy, vigorous fermentation. While the standard yeast starter size is 1 quart, up to 2 quarts is acceptable for a high gravity ale.


  • Yeast starters are highly recommended for lagers as well. Lagers ferment at lower temperatures than ales, so fermentation activity will be a little slower. Again, pitching a large yeast starter is a good way to ensure a strong, healthy fermentation at such temperatures. Like high gravity beers, a 2- to 3-quart starter can be used for lagers.


  • Finally, yeast starters are recommended when the yeast is past its "best before" date. Using the freshest yeast possible is always highly recommended, but if the yeast you're using is a little old, a yeast starter will help the yeast along its way to a healthy fermentation.

Preparing a yeast starter is relatively easy, but sanitation is of the utmost importance. Unless you are very careful to make sure everything is sterilized properly, bacteria and wild yeast will infect your starter and ruin the entire process. Here's how it's done:

  1. The first step is preparing the yeast for the starter. If you're using liquid yeast, allow your yeast to reach room temperature before proceeding. If you're using a "smack pack," you'll need to break the inner pouch. If you're using a vial of liquid yeast, this is not necessary - simply bring the yeast up to room temperature and proceed. If you're using dry yeast, boil 1 cup of water for 5 minutes, then let it cool to approximately 100 F. Stir in 2 packets of the dry yeast and cover it with plastic wrap. (If you want to see whether your dry yeast is still viable, simply boil 1 teaspoon of sugar or dried malt extract in a small amount of water and add it to your yeast-warm water mixture. After 30 minutes, the yeast should be churning as it devours the sugar. No churning means dead yeast, so it's a good idea to have a back-up plan if you use dry yeast.)


  2. Once your yeast is ready, create a starter wort by adding 1 cup of dried malt extract for every 1 quart of water. Consider the size of your yeast starter vessel. There must be room for headspace, so if you're using a 1-quart container, you'll want to use less water and, therefore, less DME.


  3. Boil the starter wort gently for at least 15 minutes, then cool it in an ice bath to the recommended fermentation temperature for your yeast. The recommended vessel for making a yeast starter is a Pyrex flask since you can boil the wort directly in the flask, but you can use any glass bottle you want as long as it can be sterilized and fitted with a stopper and airlock.


  4. Once the starter wort is cooled to the proper temperature, pour it into a sanitized Pyrex flask or a glass bottle. This is the point in the process at which sanitation is paramount. Sanitize everything that will come in contact with the yeast - the flask or bottle, the stopper, the airlock, the outside of the yeast package and the scissors that open the smack pack (if applicable, of course...).


  5. Pitch the yeast into the flask or bottle, seal it with a rubber stopper and an airlock and shake it vigorously to aerate the wort.


  6. During the yeast starter fermentation, make sure to maintain the desired beer fermentation temperature. Fermentation within the starter should occur within 12 hours of pitching, but it may not necessarily be evident given the starter wort volume. The best indication of fermentation taking place is a layer of sediment on the bottom of the flask or bottle.


  7. The best time to pitch the yeast starter to your main wort is during active fermentation or immediately thereafter, which should be in approximately 3 days. If you wait a few days between the end of the yeast starter fermentation and pitching to your main wort, revive the starter with more boiled, cooled wort before pitching.


  8. When pitching the starter to your main wort, you can either swirl the flask or bottle to bring the layer of yeast at the bottom into suspension or you can decant the starter wort and pitch only the slurry. If you plan to decant the starter beer and pitch only the slurry, it is recommended that you refrigerate the starter overnight to flocculate the yeast.


  9. To achieve a larger yeast starter for high gravity beers or lagers, additional quarts of wort can be added to the starter one quart at a time to build the yeast population even higher. Needless to say, this process will take longer and a larger bottle will be necessary for starters of this size. Like 1-quart starters, larger yeast starters can be added right into the main wort or decanted and only the yeast slurry pitched. However, keep in mind that a large starter may add more volume to your main wort than you would like, so you may only want to pitch the slurry.
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