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What is a yeast starter?
If you are a homebrewer, you have at least heard of yeast starters. You are probably even thinking that you want to make one for your next batch of nutty Peanut Butter Porter or juicy New England IPA. This is a good idea. Actually, it’s a great idea. Yeast starters are an easy way to improve the consistency and quality of your beer.
A yeast starter is a wort with low specific gravity. A mini beer. Its main purpose is to increase yeast cell counts over 24-48 hours. Secondary to that, it also acclimates yeast to the environment that it will ferment in. Yeast starters save you money and ensure you have healthy yeast to ferment your beer.
I plan to tell you everything you need to know about yeast starters. That includes:
- Why you should make a yeast starter
- When to make a yeast starter
- How to make the perfect yeast starter
Let’s get started.
Most of the mainstream yeast producers claim that they provide enough yeast to pitch into a 5-gallon batch. That means you don’t need to make a yeast starter if your ale is lower than 1.048 specific gravity. The short answer is that you should make a yeast starter if your; making an ale higher than 1.048 SG or if you are brewing a lager.
The chart below shows White Labs’ recommendation for when to make a starter and when to pitch one of their PurePitch yeast packets.
You should make a yeast starter for almost every beer you make as long as you have the time to make it. There are some caveats though. Some beers have unique characteristics that develop from pitching lower counts.
Wyeast Laboratories, Inc. defines pitch rate as “the amount of yeast that is added to cooled wort. Pitch rate is generally referred to in cells per milliliter.” It is how much yeast you are putting into a given amount of wort for fermentation. Here is a table of Wyeast’s recommended pitch rates.
|Ale||<1.060 (15 °P)||> 65F (18C)||> 65F (18C)||6 mL|
|Ale||1.061-1.076 (15-19 °P)||> 65F (18C)||> 65F (18C)||12 mL|
|Ale||>1.076 (19 °P)||> 65F (18C)||> 65F (18C)||> 18 mL|
|Lager*||<1.060 (15 °P)||> 65F (18C)||< 60F (15C)||6 mL|
|Lager*||1.061-1.076 (15-19 °P)||> 65F (18C)||< 60F (15C)||12 mL|
|Lager*||>1.076 (19 °P)||> 65F (18C)||< 60F (15C)||> 18 mL|
|Lager||<1.060 (15 °P)||< 60F (15C)||< 60F (15C)||12 mL|
|Lager||1.061-1.076 (15-19 °P)||< 60F(15C)||< 60F (15C)||18 mL|
|Lager||>1.076 (19 °P)||< 60F (15C)||< 60F (15C)||> 24 mL|
* Technique of pitching a lager warm, allowing fermentation to begin, and cooling to the desired fermentation temperature.
The amount of yeast you pitch is important. It is even more important in certain styles like lagers, Hefeweizen, and some Belgian beers.
Low pitch rates can:
- Increase levels of diacetyl
- Increase levels of higher alcohols
- Increase esters
- Increase sulfur compounds
- Lead to high final gravities
- Cause stuck fermentations
- Increase the risk of infection
High pitch rates can:
- Decrease esters
- Ferment too quick
- Cause thin body or mouthfeel
- Lead to autolysis
How to aerate your yeast starter
Another important factor in making a great yeast starter is oxygenating the wort. Yeast needs oxygen to propagate. Homebrewers do this in a few ways.
This is the most common and least expensive way to oxygenate a yeast starter. Just shake your starter flask or jar every time you pass by it or think about it to introduce more oxygen. You can also set a timer to shake it every 1-2 hours.
A stir plate is flask stand that has a spinning magnet inside. You place a sanitized stir bar inside your Erlenmeyer flask and the spinning magnet in the stir plate will cause the stir bar to spin. This creates a vortex in the starter that continuously introducing oxygen into the solution.
Using a stir plate is the best practice for homebrewers. It introduces oxygen constantly and keeps the yeast in suspension.
Now that we know what a yeast starter is when to make one, and how much to make, let’s talk about how to pitch your starter.
After you put the yeast into your starter wort, it takes 24-48 hours for the yeast to propagate. There are visual signs that this process is complete.
- Krausen has dropped
- Beer has started to clarify
- There is a nice layer of white yeast on the bottom of the flask
These visual signs are usually enough for most homebrewers. If you want to be sure that the propagation is complete, you should use a hydrometer or refractometer.
Next, you’ll need to decide if you want to decant your wort or not. If you have given yourself enough time before your brew day, best practice is to cold crash the yeast by putting it in the fridge overnight. This will flocculate the yeast, or make the yeast clump together and fall to the bottom of the flask. That way, you don’t leave yeast behind when you decant the fermented starter wort.
If you don’t have an extra day before you plan on brewing, you can pour the whole yeast starter into your wort. The downside is that you are adding oxygenated beer to your wort. Oxygenated beer doesn’t taste good. Yet, this is a pretty small ratio of the final volume, most people wouldn’t be able to taste a difference.
There are times when you will need to do a two-step propagation. A few examples are:
- You only have a small flask
- You are making a large batch of high gravity beer
- You are making a large batch of lager
- You are growing up yeast from dregs
- You are building up yeast from a slant
Doing a two-stage propagation is pretty straight forward. Then, instead of pitching that into your wort for the beer you are making, you would pitch it into another, larger starter.
There are lots of calculators online to help you determine pitch rate and how many times you need to propagate given the size of your batch and equipment. I like the yeast starter calculator that MoreBeer put together for its simplicity.
It should go without saying, but sanitation is as critical for making yeast starters as it is for the rest of brewing. We are glorified janitors after all. You should always:
Use clean equipment
- Clean with PBW, Oxyclean, or another typical brewery cleaner
- Rinse with water
Use sanitized equipment
- Sanitize with heat, StarSan, diluted iodine or another brewery sanitizer
These steps ensure that your starter does not get contaminated. Which reduces the risk of contaminating your beer.
Now it’s time for the good stuff. This is the recipe for the perfect yeast starter. For beer, it is best to grow yeast in the same environment they will be fermenting in. Our yeast starter will be a low gravity, 1.030 – 1.040 sg, unhopped beer. We will keep it between 68 to 72 degrees Fahrenheit (20 to 22 degrees Celsius) for 24-48 hours.
Here is the perfect recipe for a 5-gallon batch of beer.
- Sanitized jar or Erlenmeyer flask
- Sanitized Foil
- (Optional) Sanitized foam stopper
- ½ cup of dry malt extract
- ½ teaspoon of yeast nutrient
- 1 quart of water
- 100 grams of dry malt extract (DME)
- 2.2 grams of yeast nutrient
- 1 liter of water
- Mix dry malt extract, nutrient, and water.
- Boil for 15 minutes to sterilize.
- Pour into a sanitized flask or jar covered by a loose lid or sanitized foil.
- Allow cooling to ~70 °F (21 °C).
- Shake well and add yeast culture.
- Shake intermittently or put it on a stir plate for 24-48 hours
Pro Tip: If you have a large Erlenmeyer flask, you can mix and boil the starter in the flask so you don’t have to transfer it after boiling.
A starter is not required for most dry yeast strains. Dry yeast is usually sold with much higher cell counts than liquid yeast. Instead, you should rehydrate the yeast by adding it to warm sterilized water before pitching it into your beer.
The best practice is to decant your starter before pitching it into your beer wort. If you pitch the whole starter, it becomes one of your ingredients. Oxygen stales beer so it’s a pretty poor ingredient to be adding.
For me, both time and personal preference have played a part in whether I decant or not. If I have time to cold crash the yeast and warm them back up, I decant. If I’m in a time crunch I pitch the whole starter.
You should not use an airlock with a yeast starter. You want to give your yeast starter as much access to oxygen as possible. We recommend covering the yeast starter loosely with sanitized tin foil to keep out dust and other floating contaminants.
You do still have to worry about flying and crawling bugs though. If you have bug issues, try using a foam stopper. Either boil water in the flask while the stopper is in it to sanitize it or soaking it in StarSan should do the trick.
Making a 1-liter yeast starter is the same as any other starter. Scale the recipe from this page to make enough wort.
I hope you liked this guide and got the information you were looking for. Now go out there and make some damn good homebrew.
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