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Homebrewing: How to Make A Yeast Starter

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[Photograph: Joe Postma]

Yeast is one of the coolest ingredients you'll ever use in the kitchen. Maybe it's the beer geek coming out in me, but listen to the facts before you judge. First of all, yeast make alcohol. Like a dream, right? Second, they can produce all sorts of diverse flavors, reminiscent of lemons, spices, or butterscoth. And finally, they're not just a raw ingredient, they're actually alive. They're alive when you first add them to the beer, and they're alive when you drink them in the beer a month later. Not many other recipe ingredients can make that claim.

By creating a small, simplified batch of beer known as a starter, we can turn a little bit of yeast into a lot of yeast. Like most microorganisms, yeast will reproduce at an amazingly fast rate when put into an ideal environment. Lucky for us, the ideal environment for yeast reproduction is simple to provide: you just need water, dry malt extract, and oxygen, all at about room-temperature.

Why would we want to make a lot of yeast? As I mentioned briefly in my introduction to yeast, a single package of liquid yeast is really not enough when you're aiming to make a higher alcohol beer. Using an insufficient number of cells can cause off flavors and even infection. Making a starter will save you from having to purchase multiple packages of yeast when making these stronger recipes.

Starters are also a great way to ensure that the yeast cells that you have are healthy. When you use packets of yeast, you hope that your ingredients have all been stored properly, and that they haven't been subjected to extreme temperatures. In reality, that's not likely. When you make a starter, you can watch the amount of yeast increase and confirm that the cells you started with were not all killed by the delivery driver. The starter also gets the yeast's metabolism up and produces a whole army of new cells that are ready for action.

What You'll Need

The active time commitment for making a yeast starter is less than 30 minutes, but it should be made 24 to 48 hours before you brew your beer. The method I describe below is self-sanitizing, so there's no need to get out the idophor or Star-San you use when brewing.

The only additional piece of equipment you'll need is a 2 Liter Erlenmeyer flask, which can usually be found at homebrew shops.

You'll also need 100 grams of light or extra-light dry malt extract, tap water, aluminum foil, and one package of whatever variety of liquid yeast your recipe calls for.

What You'll Do

  1. Add ½ liter of hot tap water to the flask. Pour in 100 grams of dry malt extract. This stuff is really sticky and can fly everywhere, so if you have a funnel this is a good time to use it. If not, just be patient and try not to add too much at once. Swirl the flask until the extract is completely dissolved.
  2. Add water to the flask to the 1L mark—there are measurement markings on the side. Put the flask on the smallest burner on your stove and turn on the heat to the lowest setting.
  3. Hold the solution at just under boiling for 15 minutes. These things boil over very quickly, so keep a close eye on it. There is no need to boil the solution vigorously; the main goal is to sanitize the solution and the inside of the flask.
  4. Tightly cover the flask with a sheet of aluminum foil, and remove from heat. Let it cool for 30 minutes on the stove, and then move it to the refrigerator for a couple hours.
  5. When the flask is cool to the touch (or below 75°F), carefully remove the foil and add your yeast. Shake the flask vigorously to distribute the yeast and to get oxygen into the solution. Replace the foil, and leave it tightly covered until brew day.
  6. Intermittently shake the flask several times a day until you brew your beer. This will rouse the yeast back into suspension and dissolve more oxygen into the starter.

After 12-24 hours, you should start to see a thick white layer of yeast collecting at the bottom. When brew day comes, swirl the flask one more time to get all the cells into suspension, and simply add the entire starter to the cooled wort. As a rule of thumb, a 1 liter starter produces enough yeast to properly ferment beer between 5.5% and 7% ABV. If you are brewing a beer between 7% and 9% ABV you can double the instructions above, using 200 grams of extract and add water to make 2 liters. Be extra careful when making a 2 liter starter, because the starter could boil over very quickly. Be sure to heat the solution slowly and maintain a sub-boiling temperature.

You'll be able to use a 1 liter starter for the recipe I post next week. We'll be brewing a Robust Porter that uses the standard American "Chico" yeast. This is either White Labs WLP001 or Wyeast 1056. If you don't yet have the time or equipment to make a yeast starter before you brew this or another strong beer, that's not a problem. You can either purchase two packages of yeast or substitute the appropriate dry yeast, in this case SafAle US-05.

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