Yeast health is essential for preventing off-flavors in your homebrew. Pitching too little or too much yeast is a primary source of these yeast derived off-flavors that you are trying so hard to prevent. So you’ve decided you want to make a yeast starter. Now what?
- flask or other container
- dried malt extract (DME) – I generally use golden light extract
- kitchen scale
- stir plate and stir bar (optional)
- pot with lid
I try to make my starters four days prior to brewing. If I’m brewing Saturday morning, that means I prepare my starter Wednesday evening.
First you need to calculate how large of a starter you need to make. This is determined by variables like your post-boil batch size, original gravity of the wort, and the viability of your yeast culture. Several calculators exist to help you determine exactly how large of a starter you need:
Let’s use Beersmith. Let’s say we’re brewing a five and a half gallon batch of pale ale at 1.057 OG. After entering your recipe, click the “Starter” tab:
It will show you how many yeast cells you will need for a healthy fermentation, and it shows you all of the yeast cultures you have added to your recipe.
Select the yeast culture and press the “Edit” button. It will bring up the following screen:
We want to modify the packaging date. The packaging date is used to calculate yeast viability. As the yeast gets older, more of the yeast will die and your yeast will be less viable. You can find the packaging date somewhere on the yeast’s packaging.
Input the date and click “Ok”. If you have a stir plate (highly recommended), select the “stir plate” checkbox. It will now calculate how large of a starter you need to make:
In this case, we need to make a .89L starter. I’ll round that up to 1L to make the rest of our math easier.
We need to calculate how much DME to use. The rule of thumb is 1/10th the amount of water to yield a wort of about 1.040 in gravity. In our case 1L = 1000g, so 1/10 of 1000g is 100g.
Gather a pot, a liter of water, and 100g of DME. Add the water and DME to a pot and begin heating it. If you are using a stir plate and stir bar, add the stir bar to the wort as well. Do not turn your back on the pot as it comes to a boil as it will boil over and cleaning sticky wort off a stove top can be difficult. Carefully throttle the heat until you’re just at a simmer and boil it for ten minutes. Sanitize the pot’s lid (I hit it with some sanitizer and then throw it on the pot for the last minute or so to let the steam/heat kill the rest) and place it on the pot. If the heat is still applied, be careful you don’t boil over with the lid on. Kill the heat and move the pot to an ice bath. Chill to yeast pitching temperature. I usually fill my kitchen sink with ice water, add the covered pot, and let it go for at least an hour.
Sanitize your flask. I find a one gallon pitcher works nicely for sanitizing the funnel, scissors, and outside of the yeast packaging. Insert funnel into flask, pour in about half the wort. Carefully open your package of yeast with the sanitized scissors. Dump in the yeast. Wash the yeast out of the funnel with the rest of the wort. If you added a stir bar during the boil, drop it into the flask via the funnel. Remove the funnel and cover the flask with a piece of sanitized foil.
Place the flask onto your counter or stir plate. Let it go for 36 hours then pop it into a refrigerator for 24 hours. This will cold crash the starter, dropping much of the yeast out of suspension. When I start brewing, I pull the flask out of the refrigerator and allow it to warm to room temperature as I’m brewing. A few hours later I’m done brewing and ready to pitch my yeast. Carefully remove the foil and decant the liquid off the yeast, leaving just enough liquid to swirl around the flask to get all the yeast back into suspension. Dump the contents of the flask into your fermenter.