Making a yeast starter is a great way to ensure your beer fermentation is fast and efficient. For most new home brewers, fermentation is begun by sprinkling a dry yeast like US-05 or US-04 on top of the beer in the fermentation bucket. This method is tried and true! Most new brewers are making lower gravity beers that don’t require anything extra to ferment.
In the case of stronger beers that have a higher gravity like imperial IPAs or Imperial Stouts though, more yeast is often required to ferment the brew. A yeast starter is an easy way to achieve this.
The other time it is recommended to have a yeast starter is when you are brewing with liquid yeasts like those from White Labs or Wyeast. The shelf life of liquid yeast is far shorter than dry yeast. For this reason it is a good idea to use a yeast starter to ensure the yeast is still viable.
If the yeast that you are using is quite old or washed yeast from a previous batch, using a yeast starter is practically mandatory.
How to make a yeast starter is actually far easier than it sounds! It does take about twenty minutes of prep the day before brew day though. Put simply, a yeast starter is basically a mini batch of beer. So the main item you will need to start is Dry Malt Extract (DME), any kind will work but I prefer Pale/Light Dry Malt Extract. This is going to be your main beer ingredient and once we are done, it will make a beer with a gravity of about 1.005. The other item, which is ideal not mandatory, is a magnetic stir plate with stir bar and an Erlenmeyer flask. That being said, it is called home brewing. A kitchen pot with lid works just fine for making a yeast starter.
Before anything else, toss your yeast on the kitchen counter and allow it to reach room temperature. Like always, sanitize everything that will come into contact with your yeast starter to avoid contamination. A contaminated starter means a contaminated beer. Trust me, it’s always worth the time to do a bit of extra cleaning!
Now using a small kitchen pot, mix 2 cups of water with 1/2 cup DME. These are the quantities to use to achieve a gravity of 1.005, which is an ideal gravity for your yeast to start in. Bring your wort to a full boil and allow it to boil for 10 minutes. Some brewers like to add a few pellets of hops to the boil but I find it unnecessary as any flavors will be lost when added to the five gallon homebrew batch. After the 10 minute boil, we need to chill the mini beer just as if it were a full batch. An ice bath is the fasted method to achieve a temperature of 70- 75 degrees Fahrenheit. Once chilled, pour the wort into your Erlenmeyer flask or other mixing vessel.
Add your yeast to the wort and start the process of stirring gently. Once stirred, seal the container by wrapping a sanitized piece of foil over the top. Allow the mini beer to ferment overnight.
Put simply, that is the whole process of how to make a yeast starter! I don’t think it could get much easier. Just let the mini beer ferment overnight and it will be ready to add to your full batch of beer the next day.
As mentioned earlier, this is just one method and there are often many ways to achieve the same outcome. The point of the stir plate addition is to allow the wort to be oxygenated throughout the entire process which the yeast uses to ferment more efficiently. I have heard stories of success with simply leaving the wort in the brew pot over night with the lid on.
In the end, you have a mini batch of beer with healthy active yeast that is ready to feast on the sugars in your main batch. When it is time to ferment your 5 gallon batch of beer, all you have to do is pour the mini batch of beer into the larger batch. You will be amazed how fast and efficient your fermentation will be using this method.