Just the other day, I wrote an article about storing unopened packets of dry yeast long-term. That’s one of the easiest things: unopened packets of dry yeast last basically forever! But what do you do with an opened packet? What if you want to use part of a dry yeast packet, and save the rest for another batch?
Once opened, dry yeast packets must be stored at low temperatures. The best way to store an opened, used packet of dry yeast is to expel as much air as possible, re-seal the packet, and store it in your refrigerator at temperatures close to freezing.
Factory-sealed packets of dry yeast are by far the easiest homebrewing ingredients to store, but keeping opened packages isn’t that difficult, either.
Basically, you just need to keep the opened packages of dry yeast refrigerated to prevent exposure to moisture, keep the yeast cells dormant, and extend their lives.
The simple process for storing your opened packets of dry yeast is as follows:
- Expel as much air as possible. The easiest way to do this is to simply fold the packet up from the bottom, pushing air out of the opening as you go. Keep the packet folded tightly to prevent any air from getting inside. Air contains moisture, which will reduce the lifespan of the dry yeast. Alternatively: a vacuum sealer will get nearly all of the air out, but probably isn’t the most cost-effective solution.
- Re-seal the packet. At the homebrewing level, tape is usually the solution here. You can use any tape – just make sure to completely cover the opening with tape to keep out as much air and moisture as possible. Alternatively: a vacuum sealer will get a near-perfect seal.
- Store in the refrigerator at temperatures close to freezing. I usually just keep my opened packets of dry yeast on one of the shelves in the door of my garage fridge, but anywhere will do.
The cold temperatures of the refrigerator will put the yeast to “sleep,” keeping them dormant so they don’t undergo their metabolic processes without sugar or nutrients present – which would result in eventual death! This affects the dried yeast as well as any that were accidentally rehydrated by exposure to moisture in the air once the packet was opened.
Should You Freeze Your Opened Packets of Dry Yeast?
While freezing temperatures would slow the yeast cells’ metabolism even further, it is not a good idea to put opened packets of dry yeast into the freezer.
Any moisture in the air (and in the packet) would freeze, as well, expanding and creating ice crystals.
This expansion (and the ice crystals) can tear open yeast cells, killing them!
Freezing is much more of a concern with liquid yeast (where water is present all around them and can even kill off the colony) but it’s still something to consider with dry yeast.
Unopened packets aren’t particularly susceptible to this, since there shouldn’t be much (or any) moisture inside the packet, and it remains factory sealed. However, moisture is a concern with opened packets.
So, in summary: I wouldn’t recommend freezing your dry yeast packets. Just keep them in the refrigerator, as close to freezing temps as possible, without actually freezing them!
The Concern With Storing Open Packets of Dry Yeast
I have already outlined the three general concerns with storing dry yeast packets: Time, Temperature, and Moisture. You can read the full discussion in the “What are the Concerns When Storing Dry Yeast?” section of the previous article on storing dry yeast.
Once the packet is opened, moisture becomes the biggest concern. Any moisture introduced to the dry yeast – which can come even from humidity in the air – can rehydrate yeast cells, waking them up and amplifying the effects of time and temperature.
This is why you must re-seal the packet quickly to minimize exposure to air (and moisture) and then store it in the refrigerator, where humidity is low and the yeast will remain dormant.
How Long Does an Opened Packet of Dry Yeast Last in the Refrigerator?
I’ve seen the statement that, once opened, dry yeast will last four months in the refrigerator. However, I cannot find the source of this claim, and thus I’m skeptical of its accuracy.
In fact, I don’t think the answer to this question can be qualified absolutely, since there are too many variables at play. How much of the yeast is left in the first place? How long was it left open before re-sealing the package? How much moisture was it exposed to, and what temperatures?
I do think that four months is a safe bet, but longer storage times are most likely fine, as well. I have reused yeast packets up to a full year after they’ve been opened – but be aware this is simply anecdotal evidence from my personal experience..
According to Chris White, unopened packets of dry yeast will only lose about 4% of their viability each year. Once the packet is opened, however, any moisture in the air speeds this up dramatically.
If you re-seal the packet quickly, you can try to mitigate this by reducing exposure to moisture in the air.
Within the refrigerator, there will be humidity, and thus, moisture. However, the evaporator coils actively try to reduce the humidity inside (and push it out). If you open your refrigerator often, however, this does impact the efficiency of the refrigerator to fight humidity – and thus moisture.
So, keeping your fridge closed will keep your opened packets of dry yeast more viable for longer!
Additionally, most of us just use tape the packet closed again to seal it. Tape does a decent job of protecting the dry yeast inside, but it’s not a perfect seal. If you’re concerned about your dry yeast, you can opt to re-seal the packets with a vacuum sealer. This will remove air and moisture far more effectively – and in addition, it will create a better seal, protecting the yeast from future exposure.
(However, for many of us, that might be overkill. Especially if you plan to use the yeast again soon!)
What Can You Do About Old Dry Yeast Packets?
I previously laid out 3 methods for salvaging older packets of (unopened) dry yeast that you aren’t too sure about. Those methods will work just the same for opened packets.
You can read the full discussion in the “What Can You Do About Old Dry Yeast Packets?” section of the previous article on storing dry yeast. I will list them here for reference:
- Rehydrate the yeast before pitching.
- Salvage the colony with a yeast starter.
- Just use more packets.
I would like to emphasize that rehydrating your dry yeast is a great way to verify the viability (and usability) of old packets when you’re unsure. If rehydrating successfully got the yeast active, then they should be able to ferment the batch just fine.
Additionally, if you’re really unsure about old, half-used packets of yeast – particularly if they were not re-sealed or stored properly – don’t feel too bad about tossing it.
However, I think I would always at least attempt to use the old yeast packet. Go ahead and pitch it, and if it does turn out to be a dud (and fermentation never gets going) you can always pitch additional yeast a day or two later.
(Just be careful not to leave a high-pH, high-protein wort or must sitting for more than three days without fermenting – botulism is rarely a concern in homebrewing, but you don’t want to give it the opportunity!)
Conclusion
Once a packet of dry yeast is opened, moisture in the air becomes a concern for the cells’ viability.
However, you can still keep opened packets of dry yeast for quite a while – up to four months is commonly recommended, but in my experience, they should be fine even up to a full year later.
Just be sure to seal the packet up (with tape) and put it in the refrigerator to minimize exposure to moisture and keep the yeast dormant!
