How to Make Yeast

Last Updated: May 6, 2021 References

The process used to make yeast can seem complicated at first because it involves very specific steps, instruments, and chemicals, but it's actually very straightforward and quick to learn! You can culture yeast at home using a few basic kitchen tools and household items. Once you have your items, you can begin to make your yeast, which will take some time and requires paying careful attention. But, once you do get the technique down right, you'll be able to make your own yeast whenever you need it, like for baking your own bread, brewing homemade beer, or making other delicious cooked or baked goods that need yeast.

Method 1

Method 1 of 2:

Making Yeast from Malt Extract

The first heating: making the medium

1
Bring 1 cup of water (250 ml) to a boil. Once you have achieved this, remove water from the heat.
2
Stir 15 grams (1/2 ounce) of malt extract into the water until it is completely dissolved. Bring it to a boil for another 10-15 minutes. This will ensure sterility.
- This second boil is sanitizing the medium mixture, which is called “wort.”
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3
Add a packet of gelatin to the wort. Stir it until it is dissolved -- completely dissolved.
4
Pour some of the gelatin-wort mixture into each of the jars or dishes you’re using to make your cultures. Fill each container about 1/4 inch full. It's easiest to do this with a sterilized funnel if you're using a test tube or vials.^{[1]
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- Keep one empty jar or dish aside for use later in the culturing process.

The second heating: inoculating the medium

1
Place the jars or dishes in the bottom of the large stock pot. Make sure it has a lid! This is where having vessels with a flat bottom comes in handy. If you're using tubes with a rounded base, you'll need to rack them to stand them up.
2
Add 2 to 3 inches (5 - 7.5 cm) of water to the dish. Or enough so that the water comes halfway up the sides of your culturing vessels. Make sure the water does not get inside the jars.
- Add the jar lids carefully. Don't put them on, just in -- this will sterilize them. If you put them on, everything may explode.
3
Bring the water in the stock pot to a boil. Keep it on high for 15 minutes to sterilize the culturing vessels. Then remove vessels from the hot water using your kitchen tongs and cool completely. This may take a while, so be patient.^{[2]
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- You need to wait for things to cool to at least 40 deg. C before attaching the sterile caps, otherwise the cooling growth-medium will cause the vials to either suck the caps into the vials, or actually implode. Once cool enough, put the caps on the vials firmly. Pros generally cool for 24 hours at a slant.
- These are often referred to as “slants” by home brewers because many use test tubes and invert them at an angle so the wort-gelatin mixture inside solidifies on a slant.^{[3]
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The final stages

1
Lay out your working area. You're now going to need a number of things. It'll be easiest if you have them all at your side when you begin this process. You'll need:
- Yeast pack
- Slant vials
- An unwrapped paper clip or long needle
- Cotton ball or folded up paper-towel
- Your vial of ethyl alcohol
- Your starter vessel laid out on clean paper toweling,
- An empty, unused slant vial that has been sterilized, along with its cap.
2
Prepare the yeast as directed on the package. Each package will list different tips and instructions, so follow them carefully. You'll need to shake the yeast so it swells and forms a paste.
3
Start culturing your slants. Open the yeast packet about halfway. Wipe the needle or paper clip with the alcohol swab (this sterilizes the needle and removes contaminants that could prevent the yeast from culturing properly).
- Draw a small amount of the yeast paste into the needle or swirl the paper clip around in the yeast packet to coat it.
4
Insert the needle into the gelatin mixture and release the yeast. Work as quickly as possible during this step to prevent contamination. Avoid breathing if at all possible.^{[4]
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- Some brewers recommend placing an alcohol-soaked paper towel over the opening of the jar or dish and inserting the needle or paper clip through it into the dish to help prevent contamination when inserting the yeast.
5
Cap the jar or dish tightly. Place the jars in a clean, cool, dark place for 72 hours. Within a couple of days you will see a cloudy film on the slant surface, and a few days later it will develop into a milky white layer about 1 mm thick.
- Wipe the outside of the jars and lids with alcohol swabs. As always, everything needs to be completely sterile.
6
Loosen each jar slightly to release the pressure built up in each jar, then tighten again.
- You'll notice a slight hissing sound as you break the seal on the jar. That's excess carbon dioxide from the yeast grows as it escapes to reduce the pressure in the jar.
7
Label each jar with the date it was cultured. Store in a clean refrigerator to continue culture growth. They will keep in perfect condition for at least 3 months.

Method 2

Method 2 of 2:

Making Yeast Starter from Potato

This is a method of making yeast without a yeast package. This recipe is about right for a large family requiring more than one loaf for baking.^{[5]
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1
Boil 1 medium potato in unsalted water until done. Drain, but save the water.
2
Mash the potato. Add 1 teaspoon of sugar and and a pinch of salt.
3
Cool to lukewarm. Add enough potato water to make one quart of mixture.
4
Cover and set in a warm place. Allow to ferment.
- Note: If the starter is not rising, you can add a package of store bought yeast to speed up the process––but––it will be just as good if allowed to ferment without the added yeast.

Community Q&A

Question

How do I get the yeast from the potato mixture after it has fermented?

Community Answer

Once the fermentation is going, you can skim the foam from the surface of the bowl. This will have active live yeast in it. From there, you might want to put it in a secondary culture of flour and water to increase the size of the culture before you pitch it into a batch of bread dough.
Question

If you make the potato mixture, how long do you have to wait until it's fermented?

Community Answer

Keep it overnight. However, it depends upon climate. If it is hot it will take less time to ferment and if it is cool it will take more time.
Question

Can you define a specific temperature range for "warm"?

Community Answer

30 - 40 degrees Celsius (86-104º) should be sufficient. The 'optimal' temperature is 38 degrees Celsius (100ºF), but shouldn't matter too much.