A yeast starter is not always required, but often recommended for a healthy fermentation. The goal of a yeast starter is to increase the number of viable yeast cells to a number that is suited to the volume and gravity of your beer. These characteristics, the volume and gravity of your beer, determine how much yeast you will need for a healthy and complete fermentation. If you have never used a yeast starter before, you may not appreciate how dramatically the pitch-rate can influence the fermentation.
Often, when a yeast starter is employed, the lag time (the period of time in which there is no activity in your beer after pitching yeast) is dramatically reduced. Your beer can even start fermenting within an hour! The sooner fermentation starts, the less likely your beer will become contaminated. Additionally, when you provide enough yeast cells for a healthy fermentation, the chances of a stuck-fermentation or potential off-flavors from under-pitching are reduced. Under-pitching can stress your yeast, resulting in off-flavors and incomplete fermentations. In some instances, a starter is not required. If your beer has a low starting gravity (ie. under ~1.040), you do not need to make a starter, although it would not hurt anything. If you are using dry yeast, you also do not need to make a starter, as dry yeast sachets contain, on average, a higher cell density than the liquid pitches of yeast (better rehydrate those dry yeast packets, if you are not already). Making a healthy yeast starter comes with all the sanitation requirements as a regular batch of beer; all the equipment used for making a starter must be impeccably clean. If you are sloppy during this process, you can easily (or inadvertently) grow contaminating bacteria in your starter that will contaminate (or infect) your entire batch. The sanitation required for a starter is no less than the sanitation required for regular brewing, so do what you regularly do. There are many online calculators available to help you determine the size of starter you will need for a given batch of beer:
In general, you will need to know the volume of your batch, the starting gravity, and how many yeast cells will be required for a healthy fermentation. The standard pitch rate for ales is 0.75 million cells / milliliter / degree Plato, and double that amount for lagers or high-gravity ales. Luckily, the pitch rate calculation is built in to the calculators. The major yeast manufacturers say their vials or packets contain sufficient yeast, 100 billion cells on average, for a 5 gallon batch of 1.060 beer. This equates to roughly 0.35 million cells/ml/Plato, which is about half the recommended concentration. The vials and packets, if manufactured recently, tend to contain very healthy yeast capable of fully fermenting your beer. However, even the manufacturers will tell you to make a starter for anything >1.040 starting gravity, if you ask them. If your yeast is old - viability drops 21%/month of storage - you must make a starter.
About 24-72 hours ahead of your brew day, prepare your yeast starter. Equipment/Ingredients:
The process:
You should see activity in your starter within 12-24 hours, evidenced by krausen or foaming on the liquid surface. The starter should smell bready and yeasty. Occasionally, starters can smell tart or sulfury. If you are confident in your sanitation, the odor is probably fine. You can always taste the wort, if you would like. When you are ready to use the starter, swirl the flask/carboy to rouse the yeast and pitch the entire volume of the starter into your awaiting wort. I prefer to chill the starter after fermentation so the fresh yeast settle to the bottom of the flask. On brew day, decant the spent starter wort from the flask/carboy and pitch only the new, healthy yeast slurry left in the bottom. If you cannot use the starter immediately, you can store it in the fridge for a week or two. If longer, you may need to add fresh starter wort and repeat the process above to grow more yeast.
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