A Dry Yeast Rehydration Experiment

Some new information from Fermentis on pitching dry yeast prompted me to experiment.
You can find discussion of the new Fermentis pitching recommendations here:
https://www.beeradvocate.com/community/threads/pitching-yeast-in-low-ph.599478/#post-6311011

Method
I did a split batch to compare the Fermentis dry yeast sprinkling approach to the approach I take when I rehydrate dry yeast. The base beer is a low gravity IPA. I used an 11.5 g pack of US-05. The recipe is at the end of this post.

I evenly split 4.5 gallons of 1.056 OG wort that was mashed at 148 degrees into two stainless steel fermenters. When the fermenters had received 1.5 gallons, I stopped filling to weigh out and sprinkle half the pack of dry yeast into one of the fermenters, then resumed filling. When done filling, each vessel had 2.25 gallons of wort. At that point, I rehydrated and subsequently pitched the remainder of the yeast packet.

My rehydration approach used boiled water, cooled to 95 F. Half a pack of yeast (pre-weighed) was added to a quarter cup of this water (about 10 mL per gram of yeast). After 15 min, the yeast was gently stirred to make a more uniform slurry and allowed to rest another 15 minutes before pitching. The yeast temp was 70 F at the time of pitching.

I fermented without active temperature control. The adhesive thermometers on the fermenters showed 64 F at the time of pitching and rose to 66 F during fermentation. On the fifth day after pitching, I sampled each wort and measured gravity with a hydrometer.

Results
Before one full day elapsed, the fermenter with the sprinkled yeast appeared slightly more active in terms of krausen and airlock activity, but by 36 hours, no discernable difference was observed. On the fifth day after pitching, I measured no airlock activity or krausen was observed. The gravity of the beer produced by the sprinkled yeast was 1.005 and the gravity of the beer produced by the rehydrated yeast was 1.007.

Discussion
2 gravity points is nothing to get hung up about. I deem these to be close enough as to not really be distinguishable from a sensory perspective. I tasted each an couldn't distinguish anything different. I was surprised, given the high attenuation, that both beers still had some perceptible sweetness, but it did not seem to interfere with my enjoyment of the hoppy goodness.

This experiment supports the idea that sprinkling dry yeast is a viable option when using a Fermentis packet in a moderate gravity wort. It didn't seem to have any impact on my beer. Perhaps the pitch rate is high enough that rehydration doesn't matter. Maybe the impact of rehydration would be observed if the pitch rate were lower or the gravity of the wort higher?

In the past, I have both sprinkled and rehydrated, but not in side by side experiments. I anecdotally observed that sprinkling yeast appeared to cause fermentations to take longer to start. I always had sprinkled on top of the wort, and in this experiment, I followed my understanding of the Fermentis approach of sprinkling before the fermenter received all of the wort, adding yeast after 2/3 of the wort volume was reached and then cover the yeast with the remaining wort. Perhaps this is an important difference? It would mix the yeast into the wort a little more than sprinkling on top. In any event, either approach to sprinkling yeast is easier than rehydration.

My plans for this batch is re-combine into one keg after another week. No point in trying to maintain these as separate beers, to my way of thinking.


Recipe
Sightless Sow (an APA-AIPA tweener, harkening back to the good old days of IPA)
4.5 gallons, BIAB approach
Pale bitter water profile from BruNWater

Ingredients
6 lbs 4 oz US 2-row pale malt (Great Western Premium)
5 lbs 3 oz Maris Otter (Muntons, I think)
4 oz Caramalt (Thomas Fawcett)
0.5 oz CTZ (13.1% AA) at 75 min
1 oz Cascade (6.3% AA) at 15 min
1 oz Centennial (9.1% AA) at 15 min
1 oz Cascade (6.3% AA) steeped at 170 F for 20 min
1 oz Centennial (9.1% AA) steeped at 170 F for 20 min
1 pkg Safale US-05
1 oz Amarillo (9.2% AA) dry hop in primary for 5 days contact time
1 oz Simcoe (13% AA) dry hop in primary for 5 days contact time
1 oz Centennial (9.1% AA) dry hop in primary for 5 days contact time
1 oz Cryo-Cascade (12% AA) dry hop in primary for 5 days contact time

Mash for 90 minutes at 148
Fermentation temp started at 64 F, rose freely to 66 F by day 2, as per stick on thermometer. No active temperature control was used.

 

I think more healthy yeast is a good hypothesis for why sprinkling works, given that rehydration in wort is said to create osmotic stress. Dry yeast packets contain lots of cells, so you can get away with sprinkling. Of course n=1, so maybe that is a false assumption, but I think enough folks report sprinkling and "getting away with it" that we can be comfortable with the idea. In any event, I'll probably stop harassing people to rehydrate, as I have done in the past.

Since I use dry yeast quite a lot and can fairly easily split fermentation into two small batches, I'll probably continue to see if I can uncover some of the limitations vis a vis pitch rate and gravity and possible variations in behavior among different strains. Based on the info from Dr. Cone that @JackHorzempa posted in the linked thread in the first post, I think it is fair to say that the yeast labs would have already explored all of the ideas I have in my mind, but they don't always publicize stuff, and, well, I sort of like puttering around with my 5 gallon brewhouse.

 

Wow, surprised no one else caught that. My mistake in the original post.
First sentence of paragraph 3, boiled water, not boiled wort, cooled to 95F, was used to rehydrate.

I wish I were a better proofreader, or better yet, I wish BA would let you edit posts beyond 15 minutes.

 

Thanks to our moderator for fixing the typo for me.

 

Probably will add to it soonish

 

Your patience has been commendable!

 

Experiment #2. Almost the same deal, using Fermentis BE-256 in a Belgian pale ale. Again, a single wort was split into 2.5 gallons, with half a pack of properly rehydrated yeast pitched in one, and sprinkling non-rehydrated into the other. I unintentionally deviated from the Fermentis instructions of sprinkling dry yeast into half the wort and then topping it with the remaining wort. I forgot about that aspect of the first experiment until I had the wort evenly split into fermenters, so I just sprinkled the old fashioned way, directly on top of the wort. I did this during the 30 minutes that the remaining yeast was rehydrating. I'm expecting the same result as before: both ferment to comparable FG and no perceptible difference will be detected.

Norval, an Orval-inspired beer brewed in the Northwoods. Don't get too wrapped up comparing to some pre-existing clone recipes; I didn't go out of my way, and neither should you.

OG: 1.056 Calculated
IBUs: 45 (calculated)
SRM: 5
5.5 gallon batch (2.5 gallons per fermenter; avoided the trub-heavy remaining half gallon)

Grains and Fermentables
8 lbs Best Heidelberg Pilsner Malt
2.5 lbs Avanguard Vienna Malt
0.25 lbs Muntons Caramalt (10-14L)
1 lbs Golden Candi Syrup (5L) (added post boil)

Hops
0.75 oz Pekko, 15% AA, 60 min (34.8 IBU)
0.5 oz Crystal, 3.8% AA, 15 min (4 IBU)
0.5 oz Styrian Celia, 4.5% AA, 15 min (4.8 IBU)
1 oz Styrian Celia, 4.5% AA, Whirlpool 20 min @170F (1.6 IBU)

Dry hops (added second day of primary fermentation)
1.5 oz Crystal
0.5 oz Styrian

1 Package Safebrew Abbey Ale BE-256

Plan to package half in bottles with Brett clausenii and keg the other half without Brett, and taste side by sides periodically to observe the Brett impact. Yes, I realize this is not the strain that people typically use for Orval clones. Just what happened to be available when I was shopping.

I'll report final gravity in a week or so.

 

My prediction as well. Numbers game argument. Most of my brews are below 1.060 OG, so direct pitch of dry yeast might never be a problem, assuming 10 to 11.5 g packets and 5 gallons of wort.

BTW, that OG was measured with a hydrometer, not calculated. I measured it two ways, with a refractometer, calculating the SG, and also with a hydrometer. Not sure why I bothered to type calculated.

 

I haven’t read the entire thread yet, but, yes, I have wondered about over pitching, specifically as relates to the Belgian styles I have made with dry yeast. One thought about this experiment was maybe the directly pitched yeast will develop more Belgian character because the pitch had fewer viable cells. I just posted in a different thread about some dry kveik yeast I am buying for which the supplier recommends a 1-g pitch to a 5 gallon batch to maximize the flavors everyone wants to generate with these yeasts.