A yeast starter is a mini-beer designed to increase the yeast population to a level where no defects will be created during the fermentation. By pitching a too small population of yeast into sugary wort, the limited number of yeast will have to multiply more to consume the entirety of the sugar in the batch. This over multiplication leads to number of off flavors and fermentation flaws such as esters and leave a window open to competing bacteria to infect the beer.
Starters enable a defect-free fermentation by building the perfect population of yeast. The question is, what is a “perfect population”? It all depends on your individual batch. Lagers require more yeast than ales because they are fermented at lower temperatures, and at lower temperatures, yeast activity is significantly slower. Correctly populated lagers finish primary fermentation in 3 weeks whereas an ale finishes in 3 days. , volume of your , and type of yeast are the three major inputs to how many yeast cells you need for proper fermentation.
Step 1: Calculate
Use the calculator on the right to discover the population of yeast need for a defect-free fermentation. Depending on the yeast type and gravity of your beer, you may not need to make a starter at all! However unless you are making a 3% ABV or below beer, you will most likely have to make a starter.
Step 2: Measure
Weigh the calculated amount of dried malt extract and place it into a flask or pot for boiling. Add fresh water to the flask or pot until you reach the “Liters of Starter” number on the right. You are aiming for sugar content of 1.035 OG (8.75 Plato). Note: it may be hard to incorporate the malt extract in cold water. Try heating a small amount of water first before stirring in the DME.
Step 3: Boil
Boil your starter for at least 15 minutes.
Step 4: Cool
Bring the entire flask of starter-wort down to room temperature. If you used a pot, you must also sanitize a fermenter to receive the boiled and cooled starter-wort.
Step 5: Pitch
Pitch the yeast directly into the flask or fermenter! It will take 24 to 48 hours to be ready for use.
Step 6 (Optional): Clarify
You can put your finished starter in the fridge to separate the liquid from the yeast. This is mostly recommended for larger starters, since you will not want 3+ liters of flavorless yeast liquid diluting your beer. Place your starter in the fridge until it becomes crystal clear with a thick, white yeast cake on the bottom. Pour off most of the liquid making sure to leave a small amount for swirling up the yeast cake.
Multiple Yeast Packs
Sometimes you simply cannot reach the target yeast population with just one pack of yeast. This is especially true for lagers. Using just 1 pack of yeast will practically require you to make a full batch of beer before you make your full batch of beer! If you are making a lager that is 1.058 OG (14.5 Plato) and only plan to use one yeast pack, you must first create a 10 liter starter (which requires 2lbs of dry malt extract). If you were to use 2 yeast packs to create the starter, you would only need a 4 liter starter.
Hint: If you are an all-grain brewer, try re-using your spent mash to make a large volume starter. There is often enough sugar left in the malt for an adequate starter.
For an in-depth look at what a single yeast pack will achieve vs multiple yeast packs in starters, check out the two graphs below:
Chart and Yeast Calculation References: White, Chris, and Jamil Zainasheff. “Yeast Growth, Handling, and Storage.”Yeast: The Practical Guide to Beer Fermentation. Boulder, CO: Brewers Publications, 2010. Pgs 122, 143. Print.