When brewing, you want to get the most out of all your ingredients, and this applies to any yeast you may have remaining after a brew. With yeast being so susceptible to moisture and oxygen, is it possible for beer yeast to be frozen?
If prepared correctly, beer yeast can be stored in the freezer for up to a year. Freezing active dry beer yeast, ensure that there are no rips or tears in the packaging, and store in an air-tight container in the middle of the freezer. Liquid beer yeast requires glycerin and sanitized test tubes for storage. Test the defrosted yeast before use.
Read on to learn how to prepare your yeast for the freezer, plus how to make sure it’s still good once it’s thawed.
What happens if you freeze your beer yeast?
One of the best ways to store your yeast if you don’t need it right away is by freezing it. This is true for both active dry beer yeast and liquid beer yeast.
When storing beer yeast at colder temperatures (< 50°), the yeast cells will go into a state of suspension or a dormant type state. The yeast will remain dormant until the yeast cells are reactivated or woken up, which occurs by increasing the temperature of the yeast. This state of dormancy makes it possible for the yeast to be stored longer than it would if were in the refrigerator or the cupboard.
When it comes to preserving yeast, moisture and oxygen are not your friends. Exposure to oxygen and moisture will reactivate the yeast, which is the last thing you want while storing in the freezer.
Most freezers used today will self-defrost. Protection from defrost cycles is vital to preserving your yeast. During a defrost cycle, items will tend to warm, especially near the walls of the freezer. Even if it’s only a couple of degrees, this cycle of freeze, defrost, refreeze over some time will damage your yeast by building up moisture.
Certain types of yeast will die if not appropriately prepared for storing in a freezer. Any moisture present, like that from wort, can pierce the yeast’s cell wall damaging or neutralizing the yeast, thus making it unusable.
To store yeast properly, follow these best practices:
- Make smaller samples of the yeast to be frozen. By making smaller samples, it will lessen the amount of water and moisture in the sample.
- Add glycerol (not glycol), otherwise known as glycerin, to the samples that will be frozen. Glycerol acts as a cryoprotectant by preventing any ice crystals from forming when frozen. You can purchase glycol at most pharmacies and locations where brewing supplies are available.
- Store in an air-tight storage container
Does freezing beer yeast make it last longer?
Beer yeast lasts much longer when stored correctly in the freezer.
Freezing beer yeast makes it last significantly longer than yeast stored in the fridge or cupboard because when the yeast reaches temperatures below 50°, it will go dormant and remain suspended until reactivated.
Some brewers have observed that their yeast, when frozen, can last a few years, but try to use the yeast within a year since the yeast will lose its viability the longer it’s frozen.
Can you freeze active dry beer yeast?
Active dry beer yeast is available in packets and is generally good two years from production, although you should always check the expiration date on the packet. Correct freezing should allow you to extend that by about six months.
The absence of moisture makes freezing active dry beer yeast packets a more straightforward option than that of storing liquid dry yeast. The challenge is preventing exposure to oxygen.
Since the yeast is usually in a satchel or package, the packaging should keep any oxygen out as long as it’s not open or torn. Use an air-tight container or bag to further protect the yeast from getting wet.
How to freeze dry beer yeast
If using pre-packaged yeast, do not remove the yeast from packaging.
To freeze active dry beer yeast:
- Check the packaging for any rips or tears.
- If placing in a bag or satchel, make sure to eliminate any excess air before sealing.
- Place yeast in an air-tight container. The size of the container will depend on the space available in your freezer.
- Place in the middle of freezer, away from the walls. Temperature changes from the defrost cycle are more prevalent by freezer walls and will create unwanted moisture in the yeast.
Can you freeze liquid beer yeast?
Freezing liquid beer yeast is a more complex process than freezing active dry yeast, but it is possible.
To freeze liquid beer yeast, you will require additional equipment like glycerin, a cooler, and ice packs. The insulated cooler lined with ice packs is to maintain a constant temperature while in the freezer.
This will help offset a freezer’s defrost cycle, which can cause slight warming of the freezer, possibly causing the yeast to thaw and refreeze, which decreases the number of viable yeast cells in the sample.
How to freeze liquid beer yeast
To freeze liquid beer yeast:
- Gather yeast samples that will be frozen.
- Place a small amount of volume of water into the vials used for storing. Make sure to leave enough room for expansion.
- Add glycerol to the vials. Shoot for around ⅓ of the solution in the test tubes to be glycerol.
- Sanitize any storage equipment. Place loosely capped vials in a heat-resistant container and place the container in a pressure cooker. Place any other equipment that you will use (that can handle the heat) in the container as well. Set the pressure cooker to steam and hold for 15 minutes. Note: A pressure cooker works well since it will heat its contents to (250ºF) compared to boiling water on the stove (212ºF).
- While the contents are sanitizing, take this opportunity to sanitize your counters and other surfaces used in the process.
- Now fill up each vial with a sample of the yeast slurry. When filling, aim to fill up 80% of the vial with yeast. You want to use even less with a thicker yeast. This allows room for expansion.
- Once all vials are full, shake each vial vigorously.
- Label vials with strain, date of preparation, and generation.
- Place vials in the insulated cooler lined with ice packs.
How to unfreeze or thaw out beer yeast?
When you’re reading to thaw your beer yeast, give yourself 3 or 4 days before brewing.
To properly thaw your frozen yeast:
- First thing in the morning, take the vial out of the freezer, wrap it in a hand towel, and place in the refrigerator.
- Later that evening, remove the vial from the refrigerator and place it on the counter to allow the yeast to warm up to room temperature. As the vial of yeast warms up, prepare a small (1 cup) starter.
- Once the starter has cooled, ensure that it is aerated well for yeast propagation.
- To ensure sanitation before pitching the vial, open the cap and flame the vial’s opening with a butane torch. The flame will neutralize any unwanted germs during the transfer of the yeast to the starter.
- Pitch the yeast as usual.
The following day a krausen ring should be present to show proper fermentation. Now use this starter to make a much larger starter just as you would when using packets of yeast. It should take the big starter 1-2 days to ferment and propagate completely.
Before pitching, smell the starter. If it smells fine, you’re good to go. If not, the yeast probably developed an infection and it should be discarded.
How to tell if yeast is still good
Yeast can go bad, and it can be very frustrating if the brewer fails to recognize bad yeast before pitching. Using bad yeast will lead to wasted time and ingredients on a brew that will be ruined and discarded. So how can you tell if yeast is still good?
There are a few things a brewer can look for to see if the yeast is still good:
- Examine the yeast – The first thing a brewer would notice would be an odor. Good yeast does not smell and would have a foul odor if gone bad. Color is another indicator. If the color has darkened after thawing, then the yeast has gone bad. If it doesn’t look, feel, or smell right, it probably isn’t right.
- Test the yeast – Reactivate the yeast by mixing a teaspoon of sugar in a cup of warm water. Then add some yeast to the sugar/water mix. If there is no sign of fermentation (expanding, bubbles, etc.) within half an hour, the yeast has gone bad.
- Ferment with the yeast – Add the yeast to a couple of (sanitized) cups filled with wort. If the yeast is healthy, then within a couple of days, fermentation will take place. Once fermentation occurs, the yeast is healthy and ready to use. Just add your starter to the wort and get to brewing.