Whether you use commercial yeast or wild yeast, you really should be thinking about yeast propagation. Yeast propagation is the process of taking a small yeast sample, usually from a plate or slant and growing it until you have enough to pitch into your juice to make cider. You might be thinking, that sounds like lot of work. However, it’s really not that hard. You may also be thinking, I don’t need to do that because I just let nature do its thing. That works, until the time that it doesn’t taste they way you wanted. It also can be problematic if you want to repeat that fabulous cider you just created but can never seem to replicate it. Yeast harvesting can help in this situation as you can reuse the yeast. The problem is that your harvested yeast is evolving so if you want to go back, you can’t unless you have an earlier sample on a plate or slant. In that case, you will need to propagate it. Before I cover the propagation process I used, let’s first explore the three main reasons you would want to propagate yeasts. These are shown below.
Some yeast strains aren’t cheap. In fact, as a home cider maker, you can spend a fair amount on yeast if you buy a new packet or tube for each batch. Liquid yeasts are generally more expensive than dried yeast but even some dried yeast can be costly. Yeast propagation is a simple solution to this problem. A quick poke of a sterile loop into your yeast slurry followed by a stab of that loop into a slant or spread of across a yeast agar plate and you have just given yourself the ability to reproduce that strain again. While plates and loops do cost, you can pull many yeast colonies from a plate for propagation and they can last from one season to the next. They are a way to ensure you always have a way to access that strain. If you are all about saving money but still want consistent and repeatable results, propagating yeast is something you should do.
Are there yeasts that you’ve read about but can’t find? Maybe you made a wonderful hard cider using a wild fermentation. How would your create that same cider again? You might assume that you’d just use fruit from the same trees and you are good to go. The problem is that the yeast found on your fruit will vary each year depending on weather as well as orchard practices. Also, Saccharomyces cerevisiae, the yeast genus that generally completes most wild fermentations, is not as prevalent on fruit as it is on the equipment and in the building where you make your cider. That puts your ability to reproduce a cider from year to year at risk unless you collect your yeast and propagate it. Saving it in a slant or on an agar plate is the easiest way to ensure you can always recreate your cider. But, that will require yeast propagation. The same is true for saving those hard to find commercial strains. Once you do find them, you can save and propagate them for continued use.
The final reason you might want to be able to propagate yeast is for experimentation. There are thousands of yeasts in the world and they all have unique characteristics due to their genes. Some prefer glucose while other prefer fructose. Some ferment sugar more efficiently into ethanol. Even within a given yeast genus, many characteristics are strain specific. You can collect yeast from the bark of the trees in your front yard or you can obtain samples from a yeast culture bank, like the USDA. You can also evolve your yeast by putting selective pressure on them to try to mutate them so they perform differently. That is how beer yeast evolved. In all these situations, you need to be able to work with small colonies of yeast that you grow in size so you can ferment with them. Being able to propagate yeast gives you the ability to experiment and create hard ciders that are truly unique. If you want to take your cider to a new level, you need to know how to propagate yeast.
This year, I obtained 11 non-Saccharomyces yeast strains from the USDA’s ARS Culture Collection (NRRL) to trial for hard cider. You can see my articles on the different strains on the Yeast and Fermentation Tips page or by searching non-Saccharomyces yeast on the site. These samples were provided in slants or freeze-dried and vacuum sealed in glass tubes. Either way, I needed to propagate them in order to have enough yeast to use. I did a rough estimate that assumed if I propagated them from 30-50ml to 225-250ml, I should have enough to ferment a 1 gallon (3.8l) batch. You could probably ferment up to a 5 gallon but I decided to start with 1 gallon. If the results were good, I could try larger batches. I also plated the yeast after my first propagation step to retain the pure culture for future use. This is the material list and method I used.
- Sterile Flask – I purchased a set of three flasks, 50ml, 150ml, and 250ml. This allowed me to start with the 50ml and move up to the 250ml flask. I was doing multiple yeast propagations in parallel. I recommend you just get a 250ml and use it for the entire process. This will help avoid potential contamination as the result of moving from one flash to another and reduces the amount of sanitizing you need to perform. I don’t own an autoclave or efficient way to sterilize so I rely on sanitizing my equipment.
- Sterile Loop – I use disposable pre-sterilized loops but you could use a stainless loop that you sterilize or sanitize.
- Yeast Agar Plates – I use pre-filled sterile agar plates.
- Plastic Bottle with Cap – I use a plastic 8 ounce (237ml) bottle with a screw lid that I sanitize.
- Sterile Water – I use filtered water and heat it in the microwave but you could use bottle or boiled water.
- Apple Juice – I use pasteurized 100% organic juice. You Want to use sterilized juice to avoid growing the micro flora found in the juice. Pasteurized juice from the store is ideal. Don’t use Campden as this doesn’t really kill off all the micro flora. You could pasteurize your own juice.
- Aluminum Foil – It should be big enough to cover the opening of your container. I usually sanitize my foil versus sterilizing it.
- Yeast Nutrient – I use Fermaid O by Lallamand. It contains organic nitrogen versus inorganic like Diammonium Phosphate (DAP), which is not an ideal source for nitrogen.
- Scale or Small Measuring Spoon – It’s ideal if you can weigh your yeast nutrient but you can use a small measure spoon (1/8 teaspoon) to estimate it.
While many elements are the same, yeast propagation is different from creating a yeast starter. With a starter, you are generally revitalizing a batch of yeast. With propagation, you are growing yeast from a small colony into a large enough mass to use to ferment your batch. Whether you are growing some yeast from an apple peel, a slant, or a plate, your starting amount is small. This requires you to incrementally build your yeast’s biomass. The normal process is to double the volumetric size of your propagation solution with each step and plan that it doubles your yeast population. My estimate was that starting from a slant or small amount of yeast (<0.5g), I could achieve enough yeast for a 3-5 gallon (11-19l) batch by going from 50ml to 500ml. I actually stopped at 250ml because I was propagating for a 1 gallon (3.8l) batch. The steps will walk you through how to take as little as a few colonies and propagate it for a 1 gallon batch.
Steps: Propagating Yeast for a 1 Gallon (3.8l) Batch
- Sterilize/Sanitize your equipment.
- Heat 10ml of water and add to your flask.
- Add 0.05 grams of yeast nutrient (literally a pinch if you don’t have a scale) and swirl to dissolve.
- Add 20ml of apple juice to your flash and swirl. Cover with the foil and allow to cool.
- Using your sterile loop, remove enough colonies from your plate or slant and mix it into your flask. Avoid sticking your loop back onto the plate or slant unless you plan to use all of them. You can use a new loop or sanitize your loop with flame if you need to extract additional colonies. The goal is to minimize potential contamination of your plate.
- Swirl the liquid and cover with foil.
- Place in a warm (70-74F or 21-22C) location that is out of the way. Let is sit 24 hours but swirl whenever possible. Oxygen is currently helpful.
- After 24 hours, check for activity. It might just be cloudy, it might have CO2 bubbles, or a thin layer of yeast (whitish residue) sitting on the bottom of the flask. Swirl the flask and then add 20ml to increase your total volume to 50ml. Swirl, cover, and let rest again for 24 hours. Continue to swirl whenever possible.
- After 24 hours, check activity again. You should see more. Swirl your flask and suspend the yeast. Now is the perfect time to remove a sample for plating if you want to create a new mother culture for future use. Insert a loop and wipe that loop on your plate. Allow 48-72 hours at room temperature for the plate to grow before sealing it with a paraffin tape and storing in a refrigerator.
- Add 0.1 grams of yeast nutrient and swirl to dissolve.
- Add 75ml of apple juice. I actually use those little kids juice boxes. I store it in the refrigerator and remove it to allow it to warm up. You can squeeze the box and use the straw to add the juice. Swirl, cover, and let sit for 24 hours. Continue to swirl whenever possible.
- After 24 hours, You should be seeing a lot more activity. Add 0.25 grams of yeast nutrient and swirl to dissolve. this is about 1/16 of a teaspoon.
- Add 100ml of apple juice. Swirl, cover, and let it sit for 24 hours. Again, keep swirling whenever possible.
- After, 24 hours, you should now have enough yeast for a 1 gallon (3.8l) batch. You can add if to your juice for fermenting or put in a sanitized plastic container with a lid. Store this in the refrigerator until you are ready to use. Leave the lid cracked initially as it might continue fermenting. Tighten the lid after a few days.
- To use this, I recommend removing it from the refrigerator the night before needing it and before agitating the yeast, pour off about half of the liquid.
- After it warms up or in the morning, add another 0.25 grams of yeast nutrient swirl and top up with apple juice to the level you previously had (approximately 250ml). Allow this to sit for at least 4 hours to become active. This probably gives you enough for a 3-5 gallon (11-19l) batch but it also ensures your yeast will be robust.
You can now take harvested yeast and propagate it for use in your cider. You should never have to buy yeast again and you should be able to recreate your your unique cider batch after batch.
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