There are various reasons why you might wish to use a yeast starter. It can be used to increase the number of yeast cells which will initially be pitched, test viability or grow yeast from a different bottle beer. Making a yeast starter is very simple, but goes a long way to brewing higher quality beer.
The basic principle is to add the yeast that you are going to use to a small volume of wort and leave it, allowing fermentation to begin. Doing so will increase the amount of yeast available for brew day. It also demonstrates that the yeast you’re using is viable and ensures you are pitching healthy yeast to your wort. It also causes active fermentation to begin sooner, this lowers the chance that a wild yeast, or bacteria will be able to outcompete your yeast, therefore generating the desired flavours.
Most homebrewers make fresh wort for the starter using DME. It is doesn’t need to be spot on, but aim for a specific gravity of 1.040. This ensures that enough sugars are present, but also the specific gravity is too high. When calculating DME, it is better to use weight, rather than volume. To reach a 1.040, you want to add around 60g of DME to 475 ml of water.
Apart from sanitizer, it’s likely that you will already have all the equipment required to make a starter in your kitchen.
A suitably sized pot—anywhere from 1.5 to 2 times larger than the starter you are going to make.
- Spoon—to mix the DME in and to stir the wort.
- Large pot or sink—this will function as an ice bath.
- Large glass jar (must be able to hold a volume larger than the starter)—one with a lid is preferred.
- Funnel—to pour the wort into the glass jar.
- Aluminum foil—will cover the starter.
All you will need is your yeast and a suitable amount of DME. It isn’t necessary, but lots of homebrewers also use a yeast nutrient.
Below are instructions for creating a 16-fluid ounce starter. This amount is popular with homebrewers as it is enough to clearly ensure that the yeast is active and viable, before you pitch it. If you wanted to increase the amount of yeast you’re pitching, follow the same procedure with larger volumes.
Step 1. Clean and Sanitize
As you probably know by now, the first step when doing anything with brewing is to ensure your equipment is clean. Absolutely everything which is going to come into contact with the wort, post boil, must be sanitized.
Step 2. Boil
Bring 475 ml of water to a boil. When the water has boiled, take it off the heat and add 60g of DME and stir. Then return it to the heat and allow the wort to boil for 10-15 minutes.
Measuring out DME.
Step 3. Cool
Take the wort off the heat and place into an ice bath as fast as possible. You can use either a larger pot, like in the photo, the sink or anything else which is suitable. You’re aiming to reduce the temperature of the wort to around 70 degrees Fahrenheit, although it doesn’t need to be spot and room temperature is usually good enough.
Step 4. Pitch
Using a sanitized funnel, pour the yeast into the wort. If you’re using yeast nutrient, use it now by following the manufacturer’s instructions.
Step 5. Aerate
Put the lid on the jar and shake up the wort in order to aerate it. A couple of minutes of vigorous shaking should be enough. If you’re using a jar without a lid, stir the wort for several minutes.
Step 6. Cover
Take the lid off the jar and replace it with a sheet of aluminium foil (remember to sanitize the foil first). The lid is not suitable because it will be airtight, meaning that any CO2 cannot escape.
Step 7. Let Sit
Leave the starter for 24-48 hours to allow fermentation to take place. This is on a small scale, meaning that active fermentation takes place quickly, and you may miss it. Therefore if you don’t see it taking place, look at the sides of the jar for any yeast residue.
Aluminium foil blocks bacteria and wild yeast from entering the starter and polluting it.
Once the starter has been left for 24-48 hours it is ready, and should be used as quickly as possible. It can be left for around a week, but if it’s left for any longer, you will need to make a new one.