Erlenmeyer flasks, DME, Saccharomyces, slants and stir plates. If you are getting familiar with these terms then you are entering the world of yeast starters. Certainly a cost-savings move for the home brewer that enjoys all sorts of microbiology gadgets and geeky yeast calculations. Concocting your own yeast starter gives you better fermentation flavor control using sanitation, specific yeast strains, temperature, aeration and pitching rates.

A yeast starter is just a small scale fermentation to speed up and initiate yeast metabolism. Making a yeast starter can take approximately 12-18 hours depending on the yeast strain, temperature, yeast nutrients/food and oxygen provided. Be prepared to either brew or refrigerate the yeast slurry until you are ready to use it. A 2000ml flask allows you to make regular or large starters for larger batches or very high gravity beers. For high gravity beer, the yeast starter is necessary for a healthy and active fermentation. For large starters double the amounts of yeast, DME, yeast nutrients and water in the steps below.

As is with almost every process in home brewing, sanitation is paramount when making a yeast starter. Clean and sanitize your flasks, stoppers, yeast packs, scissors, stir plate bar, funnels, thermometers and foil. Basically anything that comes in contact with the cooled wort, flask and yeast needs to be as sterile as possible. You do not want to contaminate your yeast culture, so be very aware of your environment's cleanliness. {Sanitizers & Cleaners}

So how much yeast to use for your batch? Rather than going deep into all of the math involved in determining your pitch rate we suggest using Jamil Zainasheff's Pitching Rate Calculator. He also has an iPhone version available.

Building the Yeast Starter

Gather your supplies including a 1000ml or 2000ml flask, foam stopper, stir plate, stir bar, DME, yeast nutrients and a sanitizer like Cleanitizer, One-Step, Star San or Iodophor.

Remove the liquid yeast from the refrigerator at least 6 hours prior to pitching into the flask. For some yeast strains it will be necessary to wait up to 24 hours before pitching. Placing the packs on top of the refrigerator will give the yeast a small amount of warmth to help wake them up.

In a 2 1/2 quart pot, bring about 3 cups (720 ml) of water to a boil and turn off the heat. Add ⅛ tsp of yeast nutrient like Fermax containing diammonium phosphate and yeast hulls.

Add Dry Malt Extract (DME), 3 oz or 84g (approx. 1/2 cup). Stir the mixture until all the clumps are gone. Return the solution to a boil for 3-5 minutes to ensure the nutrients have completely dissolved.

Carefully pour the solution into the Erlenmeyer flask. Cover the top of the flask in foil. Immerse the flask in an ice bath and leave the flask submerged until it has cooled to 70F, approx. 10-15 minutes.

Once you have reached your target temperature, shake the yeast bag to break up the solid yeast bed. Spray your scissors and corner of the yeast bag with sanitizer, cut open and pitch the yeast into the room temperature wort.

Drop in your sanitized stir bar carefully down the side of the flask. Place the sanitized foam stopper in the neck of the flask allowing it to mushroom over the top. Set the flask on a stir plate at room temperature, preferably in a dark place and fermentation should start in around 12 hours. Stir plates help you culture high cell counts of healthy yeast for quicker fermentations, lower risk of infections and better tasting brew.

When fermentation occurs, the yeast starter is ready. You have helped your yeast to multiply to 4 or 5 times their initial number and they are now ready. Pitch the yeast starter as you normally would when you brew. Remember to swirl the yeast mixture in the flask very well to re-suspend all the yeast from the bottom of the flask. If you are making a lager, make sure you bring the temperature of the starter down to match the temperature of the cooled wort before you pitch, so you don't cold shock your yeast.

Note: Be prepared for highly vigorous fermentation. A blow-off setup should be used with a 6.5 gallon carboy.

If you are pitching a large starter, consider pouring off some of the starter liquid and only pitch the yeast slurry. You can chill the starter the night before to get the yeast to settle on the bottom of the flask and then either pour out or use a large pipette (sanitized turkey baster) to remove the top liquid.