How to Make a Yeast Starter

by Karl | Last Updated: May 11, 2019

Making a yeast starter is one of the best homebrewing techniques for improving your beer. While not absolutely necessary, starters can really take your beer to the next level.

If you already brew, making a yeast starter is a piece of cake. Here is why you do it, how to make a yeast starter, and the kit to make it easy.

What is a Yeast Starter?

A yeast starter is essentially a mini batch of beer. The difference is that whereas you brew a batch of beer to have a tasty beverage, you make a yeast starter to make more yeast.

So while you need to take into account flavor and aroma when brewing beer, the only thing you need to focus on with a yeast starter is growing healthy yeast.

Why make your own Yeast Starters?

  1. Grow enough healthy yeast to properly ferment your beer. Pitching a larger amount of yeast will ensure a quick and complete fermentation, prevent off-flavors, and lead to all around better tasting beer.
  2. Prepare the yeast for healthy fermentation. Yeast that have been sitting in the refrigerator for months are dormant. A starter will activate the yeast and get them ready to start fermenting beer.
  3. A starter is a way to proof your yeast. If you keep the yeast sitting around for a long time, you want to make sure it is still viable. If it is completely dead, you’d rather find out in a starter than in a 5 gallon batch of beer. Keeping your yeast properly stored is important.

What Yeast to Use?

Starters should only be made for liquid yeast cultures. Dried yeast packs already contain enough cells (220-230 billion cell count) to inoculate a 5-gallon batch, so it is not necessary to grow them. Simply rehydrate the dry yeast according the manufacturer’s instructions.

The most common liquid yeasts are the Wyeast Activator Smack Pack and the White Labs vials.

Each of these contain roughly 100 billion cell counts, but you’ll want about 200 billion for a typical 5 gallon batch of ale. The starter will get you there.

Yeast Starter Size?

The size of the starter depends on the beer that you’re making. Higher gravity beers and lagers require bigger starters.

If you’re brewing a beer with a high starting gravity (1.065+), a lager, or have old yeast, then I suggest you use a calculator (Mr. Malty pitching rate calculator) to figure out the correct size.

For a standard gravity ale, you’re safe with a 1-liter starter.

Stepping Up a Yeast Starter Table

Wort Size

The size of the starter refers to the amount of wort (water + DME) in the container after the wort is boiled and cooled. This means that you should put slightly more water into the pot than you want to end up with because a portion will boil off. 

You are only boiling for 15 minutes, so it won’t be much.  I add 100-200 ml extra to a 1-liter starter and it ends up very close. Experience is key here, but it doesn’t need to be perfect.

Amount of DME to Use

The starting gravity of the starter wort should be between 1.030-1.040. There is a very simple metric ratio you can use that will get you there: 1 gram DME for every 10 ml wort (after boiling). 

So using the 10 to 1 ratio, a 1-liter starter requires 100 grams of DME.

Equipment needed

  • Saucepan or pot. At least twice the size of the starter liquid volume is ideal because you are going to get significant foaming, just like in brewing beer.
  • Large glass container for making the starter. I use an 2 liter Erlenmeyer flask, but you could also use a growler or large mason jar. Clear is better because you can see the starter activity. The size depends on what size starter you are making, but 2 liters (~ 1/2 gallon) will do for most of your starters.
  • Liquid yeast, either White Labs or Wyeast.
  • Light Dried Malt Extract (DME).
  • Egg whisk.
  • Scale for weighing DME.
  • Thermometer.
  • Sanitizer (I use Star-San).
  • Ice.
  • Aluminum foil, cut into a square that will cover the top of your starter container.

Steps

  1. Measure out your DME and place it aside.
  2. Measure out your water and pour it into the pot; turn the burner on high.
  3. When the water starts to boil, dump in the DME and stir vigorously with the whisk in order to break up clumps. Boil for 15 minutes
  4. While the wort is boiling, prepare your sanitizing solution and sanitize your pot lid, thermometer, funnel, yeast package, aluminum foil, and starter vessel.
  5. Near the end of the boil, prepare an ice bath in your sink to cool the wort.
  6. After 15 minutes of boiling, remove the pot from the stove, place it in the ice bath, and cover with the lid.
  7. Check the wort temperature with your thermometer. When it reaches 70-75 F, remove it from the ice bath. Cooling will take about 10 minutes.
  8. Pour the wort into the starter vessel using the funnel and cover loosely with foil.
  9. Add the yeast and swirl vigorously for 30 seconds, being careful not to spill.
  10. Place the starter somewhere where it won’t be knocked over.  It doesn’t need to be protected from light the way a batch of beer does.
  11. Add oxygen. You can do this using a stir plate or just give it a shake as often as possible for those first 24 hours.
  12. After 18-36 hours your starter will be done fermenting. You can either pitch it at this point into a fresh batch of beer, or if you are not yet ready to brew you can put it in the fridge until brew day. If this is the case, see the additional steps. Otherwise, you’re done!
  13. Bonus: How to make a frozen yeast bank (for avid homebrewers)

Additional steps if you are going to keep the yeast in the refrigerator until brew day:

  1. Store the starter in the refrigerator to let the yeast settle out of the wort and form a layer on the bottom.
  2. On brew day, take the starter out of the refrigerator and decant (pour off) the wort down the drain, while being careful to leave behind the yeast cake. Leave about a 1/2 inch of wort in the vessel so you can stir up the yeast. Give it a good swirl and set aside. Let the starter come up to room temperature before pitching. Taking it out of the refrigerator 3-5 hours before you pitch is a safe bet.
  3. When your cooled wort is in the fermentor and you are ready to pitch your yeast, give the starter one final swirl and pitch it into the wort.
  4. You are done!

Important Notes and Frequently Asked Questions

Sanitation is key to the whole process. If you screw this one up, not only will you infect your starter, but you’ll infect and ruin the batch of beer that you pour it into. For the best results be clean, diligent and very careful.

Hops do not need to be added to the starter. Remember we are making yeast, not beer. Some people add hops, but in my opinion it is an unnecessary step.

Do I pour in the whole starter or decant? A very good question. It really depends. If you are using a large starter ( 2L+) or are making a lighter beer where the starter could affect the flavor, then I recommend you decant. 

If you are making an 8% stout then you won’t notice the extra wort mixed in with the complexity of other flavors.  

If you do choose to decant, make sure you chill the starter to get the yeast out of suspension. Otherwise, you will pour yeast down the drain with the wort.

You don’t need a stir-plate to make a starter, but they are a good idea. What you do need however, is oxygen in the starter. Simply shaking the starter vessel every couple hours to give it a good swirl will get you results that are almost as good as the stir-plate. This helps allow the CO2 bubbles rise to escape and also promotes healthy fermentation.

Do not use an airlock. You want oxygen exchange between the liquid and air so all that is needed is loose fitting aluminum foil. This will allow oxygen to enter the vessel, but keep bugs out. A simple foam stopper will sufice for the best results.

It is a good idea to add yeast nutrient to the starter to help promote yeast growth, however, I usually fail to follow my own advice on this one. There are minerals in the DME that will provide yeast nutrients. Additional nutrients do help, but they are not necessary.

“How long will my starter last?” The sooner you use your starter the better. The longer you wait, the more yeast cells die off and the starter becomes less effective. Try to use it within a week. If you wait longer, you should use that yeast to make another starter.

And, if you get lazy like I do sometimes, here’s the premade version that I use and recommend.

Additional Resources

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Yeast: The Practical Guide to Beer Fermentation
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Yeast selection, storage and handling of yeast cultures, how to culture yeast and the art of rinsing/washing yeast cultures. How to set up a yeast lab, the basics of fermentation science and how it affects your beer, plus step by step procedures, equipment lists and a guide to troubleshooting are included.

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06/12/2021 05:30 pm GMT
Lead marketer, brewer, dad, and husband. Pretty much an all-round awesome guy.