By Paul Kervran
There’s an old saying among brewer’s that goes “Brewers make wort. Yeast make beer”. While this is true, yeast could use a little assistance from brewers to help do their job more efficiently. Brewers often take great efforts to ensure they have the right brewing equipment, the right recipe, fresh ingredients and go through all the appropriate steps to make great wort but then simply toss in yeast almost as an afterthought. A little extra effort to prepare yeast to do their job can make the difference between good beer and great beer.
- Recommended pitching rate for an ale is 1 million cells per milliliter of wort, for every degree of Plato.
- (1,000,000) * (ml of wort) * (degrees Plato of wort)
- There’s about 3785 ml in a gallon. There are about 20,000 ml in 5.25 gallons.
- A degree Plato is about 1.004 of OG (original gravity). Divide OG by 4 to get Plato (1.048 is 12 degrees Plato).
- (1,000,000) * (20,000) * (12) = 240,000,000,000
- For an “average” wort with gravity of 1.048 with a batch size of 5.25 gallons you need about 240 billion cells
- Tip – Double this pitching rate for lagers.
- White Labs tubes and the large Wyeast Activator packs average about 100 billion cells assuming that they are in date and the viability of the yeast is good. Shipping conditions and how the yeast was store can also impact these figures negatively. Even in a best case scenario, these tubes and packs are not exactly “pitchable” as advertised.
Starters and Yeast Growth
The following are yeast growth estimates in starters from White Labs and Wyeast.
White Labs – A fresh vial added to a two liter starter will yield 240 billion cells in two days.
Wyeast – Pitching an Activator pack (large size pack) will give the following results in 12 – 18 hours:
- One liter starter = 150 billion cells
- Two liter starter = 200 billion cells
- One liter starter that is pitched to a four liter starter = 400 billion cells
These estimates are for un-agitated starters. Yeast need oxygen to reproduce. Using equipment such a stir plate, keep yeast constantly in suspension and in contact with a source of oxygen allowing increased cell growth. Estimates show that there is nearly 4X the growth using a stir plate vs. a starter just allowed to sit. Brewers without a stir plate can help increase their yeast growth by shaking the starter vessel 4-6 times (or more) to help aerate the starter. Yeast growth is increased but not to the levels of a stir plate. Regardless of the method, agitation and introduction of additional oxygen will result in a greater yield of yeast with less wort (smaller starter).
Making a Yeast Starter
Things you’ll need:
§ A small pot or a 2000ml Erlenmeyer flask
§ 4 oz. (by weight) of light DME
§ 1 quart/liter of water
§ 1 or 2 hop pellets (optional)
§ Sanitized ½ gallon growler if boiling in a pot along with a sanitized funnel
§ Aeration/oxygenation stone (optional)
§ Stir plate (optional)
Add DME, water and hop pellet(s) to pot or E. flask. (Adding DME to cool water minimizes clumping.) Swirl/stir to incorporate ingredients. Bring to a gentle boil and boil for 20 minutes. When boiling is complete, cover pot with sanitized lid or if using an E. flask, cover with sanitized foil. Immerse vessel into an ice bath to chill to about 70 degrees. With the E. flask you can jump right to aeration with a stone or by shaking the covered flask vigorously for one minute. For the wort boiled in a pot, transfer to the growler and follow the same aeration steps above. Now you can add your yeast to your starter vessel and cover with foil, an airlock or a foam stopper. Allow the starter to ferment out fully (~18-24 hours). You can either pitch the entire starter or add one extra step by refridgerating the starter overnight. The yeast will settle to a nice compact layer in the bottom of your starter vessel which will allow you to decant most of your starter liquid. The reason for decanting is to minimize the introduction of oxidized wort to your soon to be beer. This becomes more important the larger the starter. Leave enough liquid with the layer of yeast so that you can swirl it back into suspension. Allow the yeast to warm up to with 10-15 degrees of your chilled wort temperature before pitching so as not to shock your yeast. Add your starter to well aerated/oxygenated wort.