Ask Mr. Wizard

Dry Yeast Advancements


Byron Hovey — Carolina Beach, North Carolina asks,

I read the article in the May-June 2023 issue of BYO on advancements for dry yeast with much interest, but I’m still not sure if rehydrating is necessary. What is your take on it? In his book on yeast, Chris White explains why it is necessary, and how to do it. He states that pitching yeast without rehydrating reduces yeast cell viability. It seems that when I rehydrate the lag time before fermentation starts is shorter and fermentation time is shorter, which would agree with higher cell count.

sprinkling a pack of dry yeast into water to rehydrate
Rehydrating brewer’s yeast was once highly encouraged, but thanks to manufacturing improvements that advice has changed. 

This is a great example of an advancement in the brewing world that has a real effect on the way home and commercial brewers go about brewing. When I was a young and eager student in Dr. Michael Lewis’ brewing lab at UC-Davis in the early 1990s, we brewed beer using both high-quality, dried yeast and liquid yeast we propagated in the lab. During this time I learned that dried yeast generally had a bad reputation among craft brewers because some commercially available dried yeast products were contaminated with a wide array of unwanted microflora. Indeed, plating dried yeast from dubious sources was one of the things we did in the brewing lab class. When I began brewing beer for commercial sale in 1997, dried yeast was not even on my brewing radar, and I set up an account with White Labs. I’ll get back to Chris White in a bit.

Fast forward the clock 20 years and yours truly begins working in the world of brewing raw materials and starts learning about the changes in the world of dried yeast from the time in the early 90s when most brewers agreed that liquid was king. The first shocker was the realization that many well-respected craft brewers used dried yeast on the regular. I was like, “what rock have I been living beneath?” And the next shocker was comparing my go-to liquid ale strain to a dried version of a very similar strain in a 15-BBL batch of one our top sellers; the shocker was not noting any differences in fermentation rate, final gravity, or beer flavor. I was totally biased at the time and was certain that I would come up with something to gripe about! Suffice to say, I quickly got up-to-speed on things and adjusted my strong opinions.

Back to your question about what Chris White states in Yeast: The Practical Guide to Beer Fermentation he and Jamil Zainasheff co-authored about rehydration practices. I haven’t contacted Chris and don’t know what references he used to shape his views about rehydration. I do know, however, that their book was published in 2010 and there were many yeast suppliers advising brewers to rehydrate yeast at the time. The primary reason for a special rehydration process, versus just sprinkling the yeast directly into wort (aka dry pitching), is decreasing osmotic stress to the yeast cell during hydration. After the yeast cell wall and internal membranes are hydrated, they are better equipped to regulate the flow of water and wort solutes into the cell. When Chris’ book was published, this was the accepted best practice among yeast suppliers.

The thing about yeast hydration is that it takes care to perform correctly. This is not much of a challenge at home, but in commercial brewing operations hydrating yeast with 95 °F (35 °C) to 104 °F (40 °C) water for 30 minutes before use is easier said than done. Back in the early days of craft brewing, some brewers questioned the need to rehydrate because they knew that simply sprinkling yeast on top of wort usually worked fine when they homebrewed and decided to skip the step and dry pitch.

Yeast manufacturers at the time knew about the “debate” surrounding rehydration and concerns about purity. The larger companies had already been developing processes to improve brewing yeast purity, something of lesser importance to most bakers who mainly use yeast for quick production of CO2 from the massive stores of glycogen accumulated using specialized propagation techniques. And some companies advised their customers to up the pitching rate when skipping rehydration while others were working on proprietary drying methods to reduce loss of cell viability with dry pitching.

Today, dried yeast enjoys an excellent reputation around the world and is key to the production of a varied range of beers, ciders, wines, seltzers, hybrid beverages, and distilled spirits. And liquid yeast suppliers are looking at ways to sell into this market. White Labs is now selling some of their best-selling yeast strains in a dried form and promoting the benefits of dry pitching: “No rehydration or wort aeration is necessary due to the high sterol content and simple measurements of pitch rate by weight for hassle-free fermentations.” This list of advantages has been promoted by Fermentis for several years and it’s great to see more yeast experts throwing support behind a product that ha

Response by Ashton Lewis.