Yeast Storage Time Between Batches (Pro Brewing)

One of the biggest challenges and mysteries that brewers using liquid yeast face is how long yeast can be stored in between batches without risk of poor fermentations or off-flavours.

Since it is more cost effective to repitch liquid yeast, we thought it would be helpful to put together some resources and share some research we did on yeast storage time between batches of beer! 

Our simple answer is: for most yeast strains, plan to reuse it within 3 weeks, although some strains can last longer between repitches. 

Note for homebrewers: you have a lot more flexibility here, if your stored yeast is more than 1 month old we recommend building up a stir plate starter and your yeast should be OK to use for several generations. If you have any concerns about the health of a repitch however, we always suggest going back to a fresh yeast pouch. 

How long can I store my yeast in a brink between batches of beer? 

This does depend on your yeast strain. There is not much good information or data out there on how long brewery yeast will last between batches, especially at craft beer scale and with craft beer strains such as ale yeasts. 

In general, we recommend maximum storage times of yeasts based on the following table: 

Strain Category	Storage Time Recommendation	Notes
British Ales	Up to 4 weeks
German Ales	Up to 4 weeks	Kölsch - up to 3 weeks. Weizens - up to 4 weeks.
Belgian Ale/Saison	Up to 6 weeks
Kveik	Up to 6 weeks	May last longer!
Lager	Up to 3 weeks	Increase pitch rate or make a starter if over 2 weeks.
Lactobacillus	Up to 4 weeks	Check for presence of yeast cross contamination using a microscope before reusing.
American Ales	Up to 4 weeks

 

Note 1: If you are able to perform a propagation/“vitality starter” step prior to pitching, you can often extend the viable shelf life of your stored yeast up to several months.  

Note 2: Storage time is HIGHLY dependent on the viability of the yeast coming out of your fermentation. If the viability is below 80%, we suggest using the yeast within 1 week of cropping. 

Prior results 

A great study titled "Long Term Yeast Storage: Novel Approaches" was shared at the MBAA conference in 2019 by Matt Couch at Lazarus Brewing. This study showed that a pH buffer (potassium phosphate) and sunflower oil can help improve yeast viability during storage between batches. These results are promising and stay tuned for some results from Escarpment Labs testing the impact of pH buffers and nutrients on yeast storage between batches. 

Experimental Results 

We decided to put yeast storage, without any additives, to the test! We selected two strains that are not known to be super hardy, but which also aren’t super picky about storage: Kölsch, and Isar Lager. 

Fresh slurry from Escarpment Labs has a long shelf life due to how we grow and feed the yeast. Since the yeast produced at Escarpment Labs is packed with pH buffers, micronutrients, minerals, and other factors that radically enhance shelf life, we needed yeast cropped from a beer fermentation in order to obtain accurate real-world results. 

Luckily, our friends at Royal City Brewery down the road helped us out with some “gen 1” yeast slurries, freshly cropped and stored at refrigerator temperatures (2-4ºC). The yeast was tested at over 95% viability when it was cropped at the brewery, indicating this yeast was of excellent health coming out of the beer fermentation. 

For this experiment, we stored the yeast in the fridge and pulled samples at 0 weeks (fresh), 3 weeks, and 4 weeks in order to assess the impact that yeast storage time has on fermentation performance. 

We chose 3 and 4 weeks as this is around the maximum amount of time most brewers and yeast suppliers will recommend storing yeast between batches of beer. 

We then took the stored yeast slurry and pitched it into miniature wort test fermentations at a rate of 10 million cells/mL. This rate is a bit low for Isar Lager but we wanted to keep pitching rate consistent between the strains. The fermentations were run in duplicate to ensure consistency. The wort had a starting gravity of 1.042, and we monitored the specific gravity using a handheld densitometer (Anton Pair DMA35). The Kölsch was fermented at 21ºC while the Isar Lager was fermented at 15ºC. 

 

We found that the fresh yeasts fermented very well, with each strain within its expected fermentation timeline. The Kölsch strain was close to finished at day 3, and down to expected FG at day 7 (1.008). The Lager strain was at expected FG (~1.009) at day 7 as well. 

Storage impacted the lag time as well as the total fermentation time of both yeasts. Interestingly we found that 3 weeks of storage resulted in much better fermentation performance than 4 weeks of storage, suggesting that these yeasts were starting to lose vitality at this point. 

This lines up with conventional wisdom, that “regular” yeast strains such as Kölsch and Isar Lager will rep itch well for about 3 weeks, but start deteriorating in vitality after that point. 

Limitations 

We have not yet assessed the sensory impact of prolonged yeast storage. It is possible that yeast stored for 3+ weeks may also present a higher risk for fermentation off-flavours. This would be a great follow up study! 

We also had some slightly confusing viability results, as the slurries all recorded above 90% viability for the duration of the experiment using viability staining and a microscope. It would be a good idea for us to repeat this experiment and build in a secondary viability test such as viable plate counting. Nonetheless, the impact of storage on yeast vitality and performance was clear! 

What’s next? 

We’re inspired to try to find ways that brewers can extend the viable shelf life of their yeast between batches, so that brewers can get more generations out of their liquid yeast pitches. We’re also looking at quicker ways to assess yeast vitality. However we’ve been a bit dissatisfied with the traditional methods such as the acidification power test (we get variable results based on strain). Stay tuned for more practical yeast science from our team. 

The data presented in this post were collected by two University co-op students:  Karina Regimbal and Ana Ivosevic. Congratulations on your successful co-op terms Karina and Ana!