Sprinkled vs. Rehydrate Dry Yeast :: exBEERiment Results!

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brulosopher
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Sprinkled vs. Rehydrate Dry Yeast :: exBEERiment Results!

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The first question on the Danstar Yeast F.A.Q. page has to do with an issue that seems to have garnered a fair amount of healthy debate in the homebrewing community over the years-- whether one should rehydrate dry yeast before pitching or simply sprinkle it on top of the wort. The recommendation provided by Danstar echoes much of what we've all heard from well known forces in the homebrew world:

Dry beer yeast needs to be reconstituted in a gentle way. During rehydration the cell membrane goes through changes which can be lethal to yeast. In order to reconstitute the yeast as gently as possible (and minimize/avoid any damage) yeast producers developed specific rehydration procedures. Although most dry beer yeast will work if pitched directly into wort, it is recommended to follow the rehydration instructions to insure the optimum performance of the yeast.

So basically, sprinkling dry yeast directly on the wort may work, but rehydration provides some insurance the yeast performs optimally. Some studies have demonstrated yeast viability is reduced by upwards of 50% when sprinkled on wort as compared to being rehydrated prior to pitching, which is meaningful for homebrewers who often rely on fairly specific estimates of pitching rates. What, if any, differences would there be between the same wort split then pitched with rehydrated yeast versus sprinkled with dry yeast?

PURPOSE
To investigate the differences between dry yeast sprinkled directly on the wort and pitching rehydrated yeast.

METHOD
I'd been interested in making a more traditional German style lager beer with Nottingham yeast fermented cool and thought Munich Dunkel seemed like a good fit. An 11 gallon batch of wort was produced and split between 2 fermentors.

OG: 1.050
FG: 1.013
ABV: 4.9%
IBU: 21
SRM: 16

13 lbs Gambrinus Munich 10L
5.5 lbs German Pils Malt
8.0 oz Carafa Special II
4.0 oz Melanoidin Malt

~15 IBU Hallertauer Mittelfrüh @ FWH
28.0 g Hallertauer Mittelfrüh @ 20 min
28.0 g Hallertauer Mittelfrüh @ 5 min

Danstar Nottingham Ale Yeast

Mash at 154°F for 60 minutes
Chill to 58°F pitching temp, ferment at 60°F

This was one of those spur of the moment brew days that thankfully went off without a hitch. Toward the end of my 1 hour mash, just before running off the first portion of sweet wort, I threw the FWH charge of Mittelfrüh hops into the kettle. First wort hopping is a method I've been messing around with for a bit, I'm still torn as to the character it imparts as compared to more traditional bittering additions and have an exBEERiment planned to test it out.

The wort was boiled and chilled very quickly to 6°F above groundwater temp using my new Hydra IC from JaDeD Brewing (review coming soon).

I hit my target OG spot on according to both my hydrometer and refractometer.

Each carboy of wort was placed in my cool fermentation chamber to finish cooling, typical practice for me during the warmer months when I can't chill to pitching temps. It took about 4 hours for the wort to drop to 58°F. Before pitching, I rehydrated 1 sachet of yeast in 93.5°F water for 15 minutes then placed that slurry into the fermentation chamber until it dropped to within 10°F of the wort temp, this took about 20 minutes with regular swirling of the jar.

The rehydrated yeast was poured into one carboy while another sachet of Nottingham (same expiry date) was sprinkled directly into the other carboy. After about 12 hours, the dry pitch batch had what appeared to be a ring of small dry yeast globs and the rehydrated batch had some bubbles around the edge.

The only visible sign of fermentation at this point was the activity in the airlock, both burping about once every 10 seconds or so. The beers were looking very similar at 20, 36, and 60 hours post-pitch. On day 4, fermentation activity had slowed significantly and the krausen on the dry pitch batch fell before the rehydrated batch. Twelve hours later and all was looking the same again.

The temperature was ramped automatically per my hybrid fermentation profile on The Black Box controller. I took an initial gravity reading after a week in the fermentors.

My target FG was reached and remained at 1.013 in subsequent readings. After a gradual 4 day cold crash, it was time for packaging- again, no significant differences were observed at this point. I kegged and carbonated the beers as usual then they hung-out in my keezer for 2 weeks before they were evaluated.

BORING BUT SORT OF IMPORTANT...
I reworked the data collection procedure for this exBEERiment in hopes of providing more meaningful results in a less cumbersome fashion. Rather than asking all participants to provide feedback on 2 beers they taste blind, I instead had them complete a discrimination sensory evaluation known as a triangle test. Here's how it worked:

Step 1: A piece of paper with a 3 shapes (triangle, square, star) was placed on a table.
Step 2: A clear plastic cup was placed on each shape.
Step 3: Prior to the participant entering the room, the dry pitch beer was added to 2 cups (square, star) and the rehydrated beer was added to 1 cup (triangle).
Step 4: Participants were then asked to enter the room and complete a brief online survey that asked them to consider which of the beers was different then choose 1 of 4 options: triangle, square, star, or no detectable difference.
Step 5: Once the participant submitted their response, they informed me (privately) what they chose-- those who were incorrect were dismissed and those who were correct were asked to complete a more detailed survey comparing the differences between only the 2 different beers while still blind to nature of the exBEERiment. At this point, the rehydrated beer was relabeled "Sample A" and the dry pitch beer became "Sample B."

While still not up to snuff for some of the more scientific folks, this setup worked much better than I anticipated, I definitely plan to continue using it in the future. If you have any suggestions, please feel free to share them. Now, onto the interesting stuff!

RESULTS
In all, 13 people participated in the sensory evaluation portion of this exBEERiment with only 5 accurately selecting the triangle as being the different beer. A single participant detected no differences while 4 experienced star as being different and the other 3 chose square. In sum, less than 40% of the participants, all of whom are experienced homebrewers and craft beer enthusiasts, were capable of discriminating a beer fermented with rehydrated yeast from one sprinkled with dry yeast.

Of the 5 participants who did accurately choose the different beer, the large majority went on to report essentially no difference between the dry pitch and rehydrated samples in terms of appearance.

Aromatically, 3 of the survey takers experienced the rehydrated beer as being more malty and the dry pitch beer as being more hoppy. Two participants perceived the rehydrated beer as having a stronger ester/phenol character, 1 selected the dry pitch and another detected no differences. Everyone described the aroma between the 2 beers as being only somewhat similar, with 3 preferring the dry pitch and 2 preferring the rehydrated beer.

In terms of malt flavor, 2 participants perceived the rehydrated beer as being more malty, 2 thought it was the dry pitch beer, and only 1 detected no differences. These results were the same when asked about hop flavor. Three people selected the rehydrated beer as having the better fermentation/yeast character and, again, only 1 detected no differences. The dry pitch beer was selected by 2 people as having more off-flavors while 2 people detected no differences. Four participants thought the flavor of the beers were somewhat similar and one experienced them as not at all similar. When asked which beer had the better overall flavor, 3 selected the dry pitch beer and 2 selected the rehydrated beer.

The majority of participants (3) selected the dry pitch beer as having better overall mouthfeel with only 1 preferring the rehydrated beer and 1 detecting no differences.

Three of the survey takers reported a general preference for the beer fermented with dry yeast sprinkled on the wort while the other 2 preferred the beer pitched with rehydrated dry yeast.

At the end of the survey, the 5 participants were informed of the nature of the exBEERiment then asked to select which beer they believed was fermented with rehydrated yeast. Three of the 5 people accurately selected Sample A.

DISCUSSION
I went into this exBEERiment from a place of ambivalence, not just because I've rarely used dry yeast, but in my experience both approaches to pitching have yielded at least moderately enjoyable beer. Based almost solely on information gleaned from homebrew podcasts, books, and blogs, I'd say my personal bias was skewed slightly toward the rehydrated beer as being the better of the 2. In fact, I've made rehydration of dry yeast a normal part of my routine over the last year as a result of this information. I had both beers served to me "blindly" multiple times and was consistently able to accurately determine which beer was which. Like some of the participants who made it past the triangle test, I perceived the rehydrated beer as being noticeably more malty and smoother than the dry pitch beer, which had what I can only describe as a subtle apple-like tartness, perhaps as a result of acetaldehyde from stressed yeast(?). I didn't notice any differences at all in appearance or mouthfeel and neither have any real significant flaws that I could pick up.

Will I continue to rehydrate dry yeast before pitching? Yeah, I think so, despite the fact less than half of the experienced beer drinkers (BJCP judges and Cicerone beer servers included) who participated in the triangle test were unable to accurately choose the beer that was different. Do I think sprinkling dry yeast directly onto wort is poor practice? Not anymore! Some people even seem to prefer whatever character they detected from the beer fermented in this manner. I do believe, though, that with higher OG comes increased risk of yeast off-flavor and that the insurance provided by rehydration may be of benefit. Or maybe not, who knows... I smell another exBEERiment in the works!

IN CASE YOU'RE WONDERING...
Nottingham fermented at 60°F produced a pretty damn crisp Munich Dunkel with no perceptible ale-like esters you might expect from a British yeast. While the beer is good, it is missing some of that lager character I get from other strains fermented cool, particularly WLP029. I do think there are certain styles that may lend themselves to this yeast a bit more than others, maybe a rich Doppelbock or a malty Baltic Porter. For the lighter lower OG styles, I'll stick with my go-to, WLP029.

If you have any questions or comments, please don't hesitate to leave them below. Cheers!

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denny
denny's picture
Great experiment Marshall and

Great experiment Marshall and good on ya for the triangle test! Thanks for posting!

Life begins at 60....1.060, that is!