Since we began stocking Imperial Yeast a month or so ago, more than just a few people have asked for clarification of the wording on the yeast pouch that reads "Store Cold, Open Cold", since it suggests that you either don't need to, or don't want to warm the yeast to room (or wort) temperature before you pitch. As most people have been advised and read for years to pitch at as close to wort temperature as possible to avoid thermal shock, this advice by Imperial seems to be flying in the face of standard convention.
I put the question to Jessica in the Customer Service Team at Imperial, and since they likely get this question often, she had a very good explanation for me within minutes. She acknowledges that historically, the pitching temperature of the yeast and wort were thought to be ideal when they were as close as possible to each other, but she explains that extensive testing is telling them something different. When the yeast is in your fridge, at around 33F - 35 F, it is essentially dormant. When you pre-warm the package, it begins consuming its internal sugar reserves, which are not only quickly exhausted, but also produce CO2, which results in a more hostile environment inside the package and shortened cell mortality. It is thought that historically, many homebrewers have actually been underpitching, but with a warm yeast pitch that is already actively consuming its own sugars, they see a shorter lag and quicker start to fermentation, and that reinforces the idea that warm pitching is ideal. In reality, some of the yeast has already burned through its reserves and is starting to die off, leaving the remaining cells to do the balance of the work, which in turn leads to stalls, stress, and off-flavours. Some fermentations appear to begin well, then slow down and stall when the low population of yeast exhausts itself. The solution is commonly re-pitching, which can both change the final flavour profile, and add to the cost of the batch. Since all that risk is avoided when cold pitching, and it has no negative impact on either the yeast or the results, it seems like a win-win for both the yeast and the brewer. It is also worth noting that commercial brewers routinely pitch cold, taking yeast directly from the cooler to the fermenter, and if it works for them, it will work for you!!
When you consider the number of messages that Imperial might have selected to add to their packaging, I think it's a statement of their confidence in the science to put this one front and center. It would have been easy to add a reminder about sanitation, or storage temperature, or even a marketing slogan, but they choose to go against convention and present a simple but important message designed to insure optimal fermentation every time. Makes a lot of sense to me.
The best way to determine the validity of this claim is to pitch cold. However, if you choose to warm your yeast first, Jessica points out that even if there is some cell attrition in the package, starting with 200 billion cells means that in all but the most extreme cases, you will still have plenty of cells to complete your fermentation without stress.
We would love to hear your thoughts and experiences on cold pitching. Please feel free to leave your comments!
UPDATE: June 26, 2019
Following some discussion on Facebook with regards to this "radical" suggestion to pitch cold, I reached out again to Imperial, and was fortunate enough to have a phone conversation with Jess Caudill, one of their excellent Technical Support staff. One of the first things Jess reminded me of was that not too long ago, Imperial was selling yeast in cans, and the warning to store and pitch cold was there to ensure that those cans didn't swell or burst when the internal pressure increased during warming. When they changed over to the more common flexible pouch we see now, Wyeast was already in the market with a "Smack Pack", and their recommendation was to warm the package for an extended time. Imperial decided to maintain the suggestion to Store Cold Open Cold as not only a way to ensure people did not assume at ALL packaged yeast needed warming, but also based on the very positive experiences that many brewers had pitching from cold cans. However, he does make it clear that pitching cold is a recommendation that is part marketing, part practical, and that if brewers want to warm their pitch up for a few hours to narrow the temperature gap between yeast and wort, there is no harm. So, whether you choose to warm your yeast or pitch it right from the fridge, you will find that Imperial delivers a great result every time!
A huge thanks to all the support and technical staff at Imperial for helping clarify this for all of us!
For more on storage temperatures of yeast, here is a recent podcast by Brulosophy featuring Casey Helwig of Imperial Yeast and the topic of cold pitching comes up about half way into the podcast.