Author: Marshall Schott

The ability to shop for ingredients and gear from the comfort of one’s home is a huge convenience afforded to modern brewers. While online shops are generally able to guarantee a certain level of freshness, there’s only so much they can do to control the conditions in which products are shipped. Thankfully, this isn’t really an issue for most brewing wares, but it is certainly something to consider when it comes to yeast.

It’s become common knowledge that yeast is best kept cool prior to being pitched, as lower temperatures reduce the rate at which yeast consume their glycogen reserves. This is important because glycogen contributes to stronger cell walls, and hence depleted reserves can lead to weak cell walls that are more susceptible to rupturing during fermentation. When cells pop, the stuff that’s inside ends up in the beer it was intended to ferment, which can lead to off-flavors associated with autolysis.

Most brewers these days are keen enough to store their yeast in a refrigerator until use, but it’s difficult to account for the way it’s treated when being shipped. Many shops offer to wrap yeast in ice packs for a small fee, but even this has little effect when shipping takes multiple days or during warmer months.

We receive our yeast direct from Imperial Yeast, who package it in insulated styrofoam boxes with numerous ice packs, and they make sure we receive it next day. Even in the middle of summer, the yeast arrives cold. Imperial Yeast’s Casey Helwig had mentioned to me how important this is to them, and how frustrating it can be to hear that shops don’t treat their yeast with as much care as they should. With Casey in town for the holidays, the opportunity arose for a collaboration xBmt, so I proposed we test out the impact of yeast storage temperature.

| PURPOSE |

To evaluate the differences between beers fermented yeast that was stored in either cool or warm environments.

| METHODS |

In designing this xBmt with Casey, we determined an English yeast strain would be good for this variable and came up with a simple British Golden Ale recipe.

imBEERialism

Recipe Details Batch Size Boil Time IBU SRM Est. OG Est. FG ABV 5.2 gal 60 min 32.1 IBUs 5.4 SRM 1.054 1.013 5.4 % Actuals 1.054 1.01 5.8 % Fermentables Name Amount % Lamonta American-style Pale Malt (Mecca Grade) 10 lbs 95.24 Metolius Munich-style Malt (Mecca Grade) 8 oz 4.76 Hops Name Amount Time Use Form Alpha % Fuggles 30 g 60 min First Wort Pellet 4.9 Fuggles 20 g 25 min Boil Pellet 4.9 Fuggles 20 g 5 min Boil Pellet 4.9 Yeast Name Lab Attenuation Temperature Pub (A09) Imperial Yeast 72% 64°F - 70°F Notes Water Profile: Ca 69 | Mg 1 | Na 10 | SO4 97 | Cl 49 Download Download this recipe's BeerXML file

I received a box of yeast from Imperial the first week of December and immediately placed all of the pouches, which were still very cool, in my refrigerator. On December 13, after settling on the variable with Casey, I removed a package of Imperial Yeast A09 Pub and placed it on the counter in my laundry room. While we keep our heater set to 68°F/20°C during the winter months, this particular room is often a few degrees warmer due to the dryer being run most days.

Over the course of the following 13 days, I gave the pouch of yeast an abusive shake every time I walked by it, which had to have been at least 30 times, my goal being to somewhat emulate the bumps that occur during the shipping process. After filtering 2 sets of the same volume of water the night before brewing, I weighed out and milled the grain.

Casey arrived early the following morning, at which point I’d already begun heating the water. When strike temperature on either batch was reached, Casey dropped the bag of grains in and gave them a gentle stir to break up any dough balls.

Separating the start of each mash by 15 minutes, it was confirming to see both settled at the same target temperature.

Casey then moved on to weighing out the kettle hop additions for both batches.

As the mashes rested, I pulled the cold stored yeast out of the fridge to give it some time to warm up prior to pitching, a standard step in my brewing process.

Following each 60 minute mash rest, the grains were removed and the worts were brought to a rolling boil, during which hops were added as stated in the recipe.

When the 60 minute boils were completed, the worts were quickly chilled to 66°F/19°C, our desired fermentation temperature.

Refractometer readings showed the worts had reached a similar OG, with one clocking in ever so slightly lower than the other.

After 10 minutes of settling time, Casey transferred the worts to sanitized Brew Buckets.

The filled fermentors were placed in my chamber controlled to 66°F/19°C and each was pitched with its respective pouch of yeast.

Airlock activity was observed in both batches just 6 hours after yeast pitch, and they proceeded along with similar activity for the following 2 weeks, at which point neither was showing signs of fermentation. I raised the temperature of the chamber to 70°/21°C for a diacetyl rest and came back 4 days later to take hydrometer measurements showing both had reached the same FG.

At this point, I swapped out the airlocks for CO2 filled BrüLoonLocks and dropped the temperature in the chamber to 34°F/1°C for cold crashing.

Through consultation with Casey, we decided to skip fining these beers with gelatin, so I let them sit a little longer than I usually would to encourage particulate to drop out. After 4 days, I proceeded with kegging.

The filled kegs were placed in my cool keezer and burst carbonated overnight before I reduced the gas to serving pressure. After a week of conditioning, the beers were ready to serve to participants.

| RESULTS |

A total of 23 people of varying levels of experience participated in this xBmt. Each participant was served 2 samples of the beer fermented with yeast stored cold and 1 sample of the beer fermented yeast stored warm in different colored opaque cups then asked to identify the unique sample. A total of 12 tasters (p<0.05) would have had to accurately identify the unique sample in order to reach statistical significance, which is exactly how many did (p=0.048), indicating participants in this xBmt were able to reliably distinguish a British Golden Ale fermented with yeast stored cold from one fermented with yeast that was stored warm.

The 12 participants who made the accurate selection on the triangle test were instructed to complete a brief preference survey comparing only the beers that were different. A total of 3 tasters reported preferring the beer made with yeast stored cool, 8 liked the beer made with yeast stored warm, and 1 person reported perceiving no difference.

My Impressions: I began tasting these beers side-by-side the day after they were kegged and, unlike many xBmts, I thought they tasted identical. Unique in their Fuggle character with a nice toasty finish. Given the importance many place on keeping yeast cold, I wanted to ensure I gave this one a fair shake and performed 14 semi-blind triangle tests, out of which I chose the odd-beer-our 9 times. While this is fairly consistent, I have to say it was not easy at all. In fact, I found aroma to be the only place I noticed any difference, with the warm stored yeast beer having what I can only describe as a slightly sharper smell. The flavor and mouthfeel were identical to me, and I certainly didn’t pick up anything I would associate with autolysis.

| DISCUSSION |

One thing we know to be true is that warmer temperatures increase the rate at which certain reactions occur, and given yeast is a living organism, this matters equally as much prior to being pitched as it does during fermentation. Storing yeast cool leads to slower consumption of the glycogen reserves necessary for healthy cell walls, which can become thin when yeast is stored warm, leading to ruptured cells during fermentation that cause off-flavors. Indeed, tasters in this xBmt were capable of telling apart a beer fermented with yeast stored cool from one fermented with yeast stored warm, suggesting storage temperature can have a perceptible impact.

In addition to the effect on flavor and aroma, another reason it’s recommended to store yeast cold has to do with performance. Considering the hastened reaction rate that comes with warmer temperatures, it makes sense the yeast pouch that sat in my warm laundry room for 2 weeks would be less viable at pitch than the yeast that stayed in the fridge, which would presumably result in longer lag, less active fermentation, and potential attenuation issues. Interestingly, this wasn’t the case at all, both beers showed signs of activity at the same time, fermented vigorously, and finished at the same FG.

I’m in the admittedly fortunate position of being able to order yeast directly from Imperial Yeast, who ship next day with plenty of ice, so I’m able to get it in my fridge before it warms up. Based on my experience with these beers, and the fact I have a fridge with a dedicated yeast space, I certainly have no plans to store mine warm. However, if I were to order yeast in the middle of summer and the ice pack happened to melt during the 3 day shipping process, I wouldn’t be terribly concerned, probably toss it in a starter to ensure it’s alive and roll with it.

Unfortunately, Casey was back in Portland when these beers were ready and was unable to try them for herself, but I did ask if she’d share her thoughts on this xBmt:

I had a great time hanging out and making beer with Marshall! I’ll be honest, I really didn’t want this to work out. Storage temperature is so important for healthy yeast and successful fermentations. Ideally, yeast is stored in a fridge around 33-38°F/1-3°C and used as fresh as possible. If shipped from an online retailer, it’s paramount to buy ice packs and pay for expedited shipping.

We sent Marshall two packs of A09 Pub that were packaged on the same date, one stored warm for 2 weeks while the other stayed in the fridge. They were pitched at the same time and in a matter of hours both were fermenting. As you can imagine, this was both frustrating and also kind of awesome. While it’s great the warm stored Pub started fermenting around the same time as the properly/cold stored pack, a testament to the high cell count, viability, and quality of Imperial Yeast, we’ll be sticking to recommending people store yeast in ideal conditions.

If you have any thoughts about this xBmt, please do not hesitate to share in the comments section below!

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