Yeast is a vital single-celled organism for bakers and brewers around the world, as it is capable of transforming sugars into carbon dioxide and alcohol. You can make your own sourdough for bread with just flour, water and constant care. Brewer's yeast culture, on the other hand, is a bit more complex because it needs a sterile environment, but it is described in this article for use by more experienced or ambitious home brewers. Both of these yeasts can survive for months in the refrigerator and will allow you to bake perfect bread or prepare an excellent beer for many, many times.
If you want to know how to make yeast before cooking bread, you can read this article.
Steps
Method 1 of 2: Growing the sourdough
Step 1. Choose a large, clean jar
In theory, you should use a glass jar with a minimum capacity of two liters, since the trigger grows rapidly and you may be forced to throw it away if the container is too small. You can also consider plastic or porcelain stoneware jars, but glass remains the easiest material to clean, as well as being transparent and you can control the process. Sterilize the jar in boiling water if the material is heat resistant. However, it is also sufficient to wash it with very hot water and soap, taking care to rinse it carefully.
Step 2. Pour 120ml of dechlorinated water
If the tap water is treated with chlorine, buy tablets to add to eliminate it, or leave the container open for at least 24 hours. The minerals found in "hard" waters help the development of the yeast culture, so distilled water is not recommended.
If you can't get water with the ideal characteristics, use any type of drinking water
Step 3. Add 110g of flour and mix vigorously
Use 00 flour if you want to make white bread, or wholemeal for black bread. Flour naturally contains yeast strains, microorganisms that produce carbon dioxide and other substances that allow the bread to rise and flavor it.
- Stir vigorously to add air to the mixture.
- Other types of flour can be used to obtain triggers with different flavors, including wholemeal rice flour and spelled flour.
Step 4. Add unwashed organic grapes (optional)
If you are using white flour instead of wholemeal, your primer may be deficient in certain types of yeast that provide a sour, “yeasty” flavor. So you can try to compensate for this lack by adding some fruit; the most common is a handful of grapes. Use only that from organic cultures, not treated with pesticides or waxes, so you can add it without washing it.
Although grapes contain yeasts, how these can thrive in the initiation of mother yeast is still a matter of debate. Some bakers recommend this step, while others question its effectiveness
Step 5. Cover the jar but don't seal it
Do not use airtight lids, as a well-primed sourdough produces gases that could break the seal. Also, yeasts need oxygen to live. Instead, cover the container with gauze, kitchen paper, or a clean tea towel secured with a rubber band. As a last resort, use the lid of the jar without tightening it completely.
Step 6. Leave the mixture in a warm place for a couple of days
To encourage yeast activity, the primer must remain at 21 ° C. After this time, the mixture should be frothy or bubbly with a typical odor. Some triggers take longer to activate, so don't worry if you don't notice any changes yet.
If your home is quite cold, keep the pan near the stove or radiator (but not close enough to cook the mixture). Yeasts thrive in a warm environment, but die if overdone
Step 7. Add 120ml of water and 110g of flour
Do this gradually, in small quantities and mix carefully. Cover the jar again and let it rest for another 24 hours, so the yeast will "eat" the new food you provided.
Step 8. Replace, every day, part of the primer with flour and fresh water
Remove part of the primer and leave about 120 ml of content in the jar. At this point it is still not safe and effective to use in the kitchen, so throw away what you take away. Add more water and flour to replace it, the exact amounts are not important, but keep a 3: 2 ratio of flour and water. Do not add a fresh mix that is more than triple the amount of the old mix.
Step 9. Check the crop
At first, the trigger produces a yellowish liquid, or it could smell like alcohol. Hopefully all of this will disappear within a week, and as the colony of yeast grows, the scent should be more like that of raw bread. When the yeast has stabilized, it should double in volume between "one meal and the next". Continue to feed it with water and flour until it reaches this state, it will take at least a full week; in this way you avoid that competing microorganisms take over. Some mother yeasts are not ready for a month or more.
If the mixture produces a dark brown liquid, the yeast has run out of food. Throw away the liquid and feed the sourdough more often or with larger amounts of flour and water
Step 10. Move the sourdough to the fridge and feed it less frequently
When the mixture doubles its volume at each "meal" for three consecutive days and no longer produces unpleasant odors / liquids (other than those of bread), close the lid of the jar tightly and put it in the fridge. The yeasts will remain dormant, slowing down their activity and it will be enough for you to feed them once a week with flour and water, throwing away a part to avoid overfilling the container. As long as you continue to feed the sourdough, you can keep it alive in the refrigerator for an unlimited time. By doing this, you will have sourdough to make your bread for months or even years.
Primers made with brown rice flour should be fed every 2 to 3 days, even if they are in the refrigerator
Step 11. Use sourdough in bread recipes
Before using some of it in the bread dough (instead of the chemical or commercial one), you must reactivate it by placing it at room temperature and covering it with gauze or kitchen paper. You will also need to feed him at least three times at 8-12 hour intervals. Knead the bread very well to activate the formation of gluten which will make it elastic and thin: you should be able to pull the dough so much that you can see through it without breaking it. Since the mother yeast has a slower action than the commercial one, let the dough rest for at least 4-12 hours, or even a full day, if you want a more acid-tasting product.
- Be careful not to overheat the dough because you could kill the yeast. Touch the dough from time to time if you are using a planetary mixer, as you could heat it too much.
- You can also use mother yeast in other recipes that involve the use of flour, but know that it will give a sour taste typical of yeast. For example, many people like slightly sour pancakes made with sourdough, which would otherwise be thrown away during the feeding process.
Method 2 of 2: Grow Brewer's Yeast
Step 1. Start with a high quality yeast culture specific for beer
Although it is also possible to start with a commercial liquid product, the process is too difficult and time-consuming if you start with such a strain. Brewers usually start yeast cultures from sediments of a previous particularly good brewery, buy them in craft breweries or source particularly rare and expensive strains, then grow and use them multiple times.
- Growing a long-term yeast strain is a challenging and time-consuming task. It is not necessary for you to brew the beer at home, but you must maintain certain environmental conditions favorable to the strain.
- Remember that the yeast sediments that you can find in the bottom of a beer bottle may not be the same as the yeast used for the initial fermentation and the results you will get may be disappointing.
Step 2. Work in a clean environment
Airborne contaminants, such as bacteria, can ruin your crop. Avoid wet areas and places where you prepare food (kitchens and basements). Close the windows of the room you have dedicated to this activity, especially if the season is warm.
Always wash your hands with antibacterial soap before handling yeast
Step 3. Clean and sanitize surfaces
Wash the table or countertop as thoroughly as possible. Kill all microorganisms with a disinfectant such as denatured alcohol. Wait for it to dry.
Step 4. Get everything you need
The easiest way to do this is to purchase a brewer's kit which might also contain a yeast primer and instructions. If you decide to buy each piece individually, check the “Things You Will Need” section for details. Search pharmacies or contact companies that produce laboratory supplies (check the yellow pages).
- In some countries, the purchase of laboratory equipment by private individuals is strictly supervised and monitored.
- Agar powder is available in many oriental food stores. If you can't get it, you can use neutral gelatin powder, however a yeast culture on a gelatinous base requires storage in a refrigerator to prevent it from melting.
Step 5. Sterilize the containers
Use steam for those that are made of heat-resistant glass and the corresponding lids; you can use a pressure cooker: 10 minutes will be enough to kill any contaminants. Petri dishes are widely used although any small glass container is fine. Test tubes are often included in brewing kits for just this purpose.
- If you don't have a pressure cooker, immerse the containers in boiling water for half an hour; however, this is not a very effective method and could ruin a large number of crops with mold.
- If you have sterile plastic bags to store the containers in, you can sanitize them well in advance.
Step 6. Wait for the material to cool and then place it in contact with an open flame
This step is critical to ensure near-perfect sterility and prevent the yeast culture from becoming contaminated with other microorganisms that could take over. You can use a propane torch or other type of portable tool that emits a high-temperature flame (so the regular lighter is no good). Put the edge of the container in contact with the fire.
Step 7. Use fresh or distilled water
If the water from your tap is hard, that is, it contains a lot of limestone and carbonate minerals, it could promote bacterial growth within the yeast culture. To be safe, use distilled water or measure the pH of the tap water, making sure it is not higher than 5.3.
Step 8. Boil 240ml of water with 60ml of dry malt extract
It would be better to do this in a pressure cooker to avoid evaporation and reducing the amount of water. Alternatively, use a pyrex balloon or a saucepan. Add the malt extract and mix to dissolve it. Bring to a boil for 15 minutes, lowering the heat to prevent the contents from overflowing.
This solution is called "priming must"
Step 9. Turn the heat down and mix 2.5 g agar powder into the solution until it dissolves completely
The primer must already contains all the nutrients necessary for the yeast to grow, but the agar powder thickens the mixture and makes it similar to gelatin, so that the yeast can cling to it. Remember that densification does not occur at this stage.
Use neutral gelatin powder only if you are unable to get agar powder, as the gelatin melts at room temperature
Step 10. Bring the mixture to a boil again
You will have to "cook" it for another 15 minutes without ever losing sight of it to prevent it from overflowing.
Step 11. Remove the container from the heat
Wait for the mixture to reach 50 ° C, or less if you use gelatin instead of agar. It should thicken without solidifying completely.
Step 12. Fill each sterile container with a small layer of mixture
Petri dishes should be filled to about ¼ of their capacity with the primer must, while larger containers do not need a denser layer.
Step 13. Cover the containers and wait
You can use the original petri dish lids or wrap them in cling film. Wait for the mixture to cool for about half an hour and check that it solidifies thanks to the agar powder. When you can turn the containers without the wort flowing, they will be ready.
Step 14. Sterilize inoculating loops
You can find them in lab supplies stores, these are sticks at the end of which there is a metal ring and are used to transfer microorganisms such as yeasts. To sterilize them, hold the ring over a flame until it becomes incandescent. Wait for it to come back to room temperature or a little more by placing it in a shallow saucer filled with isopropyl alcohol or wrapping it in a swab dipped in the same liquid.
- If you don't cool the loop, the heat will kill the yeast.
- If you cool it in water or in the open air, there is a greater chance that it will become contaminated again with microorganisms that will instead be killed by alcohol.
Step 15. Gently rub the loop on the liquid yeast sediment
Do not try to take a visible amount of the product. All you have to do is gently rub the metal ring on the surface of the sediment to get some liquid.
Step 16. Transfer the yeast to the surface of the primer must with great care and attention
Try to leave the container open only for the minimum time necessary, moving the inoculation loop just above the surface of the gelatinous substrate. This transfers some (hopefully) germ-free yeast onto the nutrient-rich substrate. To minimize the risk of contamination, close the lid immediately. Turn the Petri dishes upside down or tilt the tubes about ¾ of the seal.
This process is called a "smear" in laboratory jargon
Step 17. Repeat the loop sterilization process and add another yeast smear to a second container
Continue like this for all available containers, but remember to heat and sterilize the loop each time by cooling it in alcohol. Home grown yeast cultures have a very high risk of contamination, so the use of multiple separate containers increases the chances of success.
Step 18. Check the crops over the next few days
Store the containers at 21-26 ° C because this is the ideal range for the growth of yeasts. Discard any crops that have fluff or mold or appear to be non-living even after several days. A good culture produces a milky layer on the surface and you may see individual yeast colonies forming patterns or dots.
Step 19. Move live, healthy crops to the refrigerator
Now that they have been activated, seal the containers with duct tape or some other material that blocks the passage of light, as this can ruin and even destroy the yeast colony. Store them this way in the refrigerator at 1-2 ° C or slightly higher to slow down their growth and prevent them from running out of nutrients. When you want to use yeast for brewing, remove a container from the fridge well in advance to bring it back to room temperature before adding it to the wort.
