Why Do I Need A Yeast Stir Plate?

This page is intended to give the beer home brewer some insight into the purposes and methods of using yeast starters in the process of making home brewed beer.

Most home brewers buy liquid yeast in the so-called pitchable tubes or smack packs. Yeast in this form generally does not contain enough viable cells to achieve the pitching rates required for successful fermentations. As a consequence, most home brewers chronically under pitch, perhaps by a factor of 20! Good brewing practice calls for a count of one-billion cells per liter per degree Plato. For a standard 5-gallon batch, this means you should be pitching in the neighborhood of 200 billion cells into your cooled wort. Higher gravity worts and lagers require even higher cell counts. A starter becomes necessary for a number of reasons:

  • Poor storage temperature control and using yeast close to its use by dates diminishes the viable cell counts in a liquid yeast product.
  • A starter will help you proof yeast by allowing you to visually determine if the yeast you purchased, maybe a month, ago still has enough viable cells for fermentation.
  • Low pitching rates may result in infected finished beer, higher than normal final gravity, excess production of objectionable flavors caused by fusel alcohols, esters, diacetyl and sulfur compounds.
  • A starter allows you to step up the cell counts to the appropriate level for the style you are brewing. As wort gravity increases, the need for more yeast increases also.

A typical yeast starter is made using a ratio of 1 gram of light dry malt extract (DME) to 10 mL of water to give a solution with specific gravity of 1.030. For a 1.5-liter starter, one would use 150 grams of DME, boiled in water for 10 minutes, then cooled to 70 F. Details on preparation of yeast starters can be found at the Maltose Falcons website as well as the HBD website.

The next step up in your yeast starter regimen is to stir the starter continuously, which grows more yeast in a shorter period of time. Studies show that stirred starters have up to a ten-fold increase in cell counts than a non-stirred starter. Why is this so?

  • Stirred starters continuously aerate the wort. Oxygenated wort is essential for yeast propagation
  • Stirring knocks carbon dioxide, a by-product of yeast growth, out of suspension. Carbon dioxide in solution inhibits yeast growth.
  • Stirring keeps the yeast in suspension and in constant contact with nutrients.

Yeast Graph

Recommended reading for more information on yeast propagation is MB Raines-Casselman's article Yeast Propagation and Maintenance: Principles and Practices



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This product comes with a lifetime repair or replacement warranty. Simply put, if The StirStarter fails to perform for ANY reason, return it to me and I will repair or replace it at no charge. Customer satisfaction and great beer are my goals!