Dry Yeast Rehydration and O2 experiment

After some discussion in thread: https://www.homebrewtalk.com/showthread.php?p=472399 I've decided that it's been long enough with no well-documented experimenting at least within our ranks.

My next brew is going to test the effects of dry yeast rehydration on lag times, fermentation completion time, and overall attenuation.

I'm going to do 2 gallons of 1.050 or so wort split 4 ways. Pitch rates will be .5 grams dry weight per 2-qt sample, exactly half the normal pitch rate of 10-11 grams per 5 gallons. Expected results (hypothesis) in parenthesis.

1. O2 devoid, Rehydrated (high starting cell count, anaerobic conditions, expect shortest lag, low/moderate attenuation)

2. O2 devoid, Dry Pitch (low starting cell count, anarobic conditions, 2nd shortest lag, lowest attenuation)

3. O2 injected, Rehydrated (high starting cell count, aerobic conditions, 3rd shortest lag, most attenuative)

4. O2 injected, Dry pitch. (low starting cell count, aerobic conditions, expect longest lag time, moderate attenuation)

I'm choosing a pitching rate that is less than usual to exagerate the results. Let me know if you think it would be better to stick to actual pitching rates of 1 gram per .5 gallons.

Just to summarize, the order in which expect visible fermentation to begin is 1,2,3, 4 but the attenutation order from most to least is 3,4,1,2 based on the overall cell count that will be acheived given the conditions.

I hope this generates some good discussion and hopefully also clears up any misinformation that might be circulating. Hold on to your hats.

Good, thanks. Let me know when you're brewing this too

Sounds good Bobby, do us proud . What yeast are you planning on using for the experiment? Oh that brings up a point. This should probably be done over a span of a few strains as some strains may be particularly capable of certain conditions as outlined by your experiment.

Thinking about this more, if you just focus on one strain, perhaps using one which has a reputeably long lag time to begin with might serve you better. (That way you avoid condensing your time scale...things make less sense so close together if you get what I am saying).

You should also see if you can get some blind taste tests too. I imagine (and hope) that this will produce some different flavors too. Also, if you had the ability, I would suggest doing a normal O2, recommended pitch rate as some sort of 'control.'

Sounds great. Can't wait to hear the results.

It should be interesting to see the results. When I started rehydrating nottingham according to directions instead of pitching directly into wort my lag times went down to a couple hours.

Beerrific said:

You should also see if you can get some blind taste tests too. I imagine (and hope) that this will produce some different flavors too. Also, if you had the ability, I would suggest doing a normal O2, recommended pitch rate as some sort of 'control.'

Sounds great. Can't wait to hear the results.

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That is possibly another discussion though, but it does need to be made clear in the course of the experiment and when dealing with the results that this is merely to test the aforementioned aspects of the fermentation process. Things like flavor, etc, all should be seperate experiments imo.

Actually, no you're right. A blind taste test should be done to see what is going on flavor wise as a result of each test. But I do think that the actual measured results should be clearly portrayed without the influence of the taste factor and visa-versa.

I will probably use Danstar Windsor. For one thing I have it on hand and don't use it much. The real reason I want to use it is that it is generally a low attenuator so I hope that it will also amplify the differences between the samples (in addition to pitching half the recommended amount).

With those results, one could easily extrapolate the effects of using a higher/lower pitching rate, more or less oxygen, and a differently attunating yeast.

I am all for discussing additional potential variations in the experiment but I also want you to keep in mind how much work will go into even the limited four samples in both making sure I limit all potential out of scope variables as well as documenting and publishing the results. Even doubling the number of samples (adding only one more variable) is like taking on a part time job ;-)

By the way, anyone that wants to donate to the cause... I am short on 1-gallon glass jugs. I only have three of the four required for the experiment. If you have a "friend" that drinks Carlo and Rossi jug wine... I'd appreciate the empty.

Bobby_M said:

I am all for discussing additional potential variations in the experiment but I also want you to keep in mind how much work will go into even the limited four samples in both making sure I limit all potential out of scope variables as well as documenting and publishing the results. Even doubling the number of samples (adding only one more variable) is like taking on a part time job ;-)

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Indeed. And I didn't mean to imply that is what you should do but rather something to keep in mind when extrapolating your results. In other words, having that clear when you present your results might be beneficial.

I think the Windsor is a good call, (in addition to the point you make for using it) it has always given me good, consistent results and has a fairly normal lag time (in my experience) when compared with some of the other strains I regularly use.

At any rate, thanks again for taking the time to do this!

I finally got my four 1-gallon jugs and found some good timelapse software so I'm ready to do this experiment. I was originally going to skip the hopping and stuff but I figure I might as well bottle it. I'll mark the bottes #1-4 and invite some club members to blind taste it and provide feedback. Stay tuned.

Awesome! Very neat experiment, Bobby_M - clear hypotheses, falsifiable predictions and a subject matter of vital importance . I'll be really interested to see what you find.

I only have two fermenters so I can't replicate your 2x2 design, but on my next batch I'll split the oxygenated wort, and re-run your dry pitched yeast vs. rehydrated comparison. See what convergent evidence there is. I guess for generalisability's sake we should try this with a variety of yeasts, to see whether different yeasts perform in similar ways. I'll probably be using Safale US-05 or Danstar Nottingham.

I think your taste tests would be interesting. What taste differences would people expect to find?

Just had a thought. Will it matter that the rehydrated samples will have a slightly lower gravity than the dry-pitched batches (because of the extra liquid from the rehydrated yeast)? Maybe to rule this out as a potential confound you should add an equivalent amount of sterilised water to the wort of the two dry-pitched samples before adding the dry yeast. I don't expect it would make much difference either way, but it would rule out one potential confound to the results.

Love this type of thinking. Could prove or debunk a few key yeast issues.

Any chance you could do a fifth one, with a starter?

I would if I had a 5th jug.

Nice experiment. Though I'm not using dry yeast, I'm curious about the results though.

kenb said:

Any chance you could do a fifth one, with a starter?

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I'd actually suggest that you take a bottle, fill it with some wort and badly overpitch it with the dry yeast. Keep this one warm and shake it regularly to rouse the yeast. You want to ensure that the yeast ferments it all the way and you can measure the limit of attenuation for the wort that you produced.
This sample is not for bottling. You only need enough to take a gravity reading.

Excellent suggestion. It's easy enough to sparge a bit more and I'm already going to have a ton of leftover yeast.. I'm planning on mashing in a crock pot on a contoller with 1º differential at 148 for high fermentability so that big pitch will verify the max attenuation.

Ok, it's way early to make a full report but I can say without a doubt now that rehydrating dry yeast makes a HUGE difference vs. dry sprinkling. Details to follow. Here's the first frame of my timelapse:

Cool! Is the difference that the wet pitches started quicker than the dry ones?

Also looks like the well oxygenated samples have much better krausen than the crappily oxygenated ones. We're learnin' stuff here!

Well, the "krausen" you see is really just surface bubbles from the O2 injection which occured like 10 minutes prior to the pic.

Yes, the two that were rehydrated started significantly sooner. You'll see that in the full report and video probably later this weekend. I just took the first round of gravity samples and I'll probably do the same on Sunday morning.

I'm assuming you followed normal sanitation procedures, right? Wild yeast could really throw its wrench in...

Certainly. Experiment or not, this is still beer and I'm not going to let any beasties get hold. I did everything the same except I icewater batch chilled instead of CFC because it was a small stovetop brew.

Great experiment. I've subscribed to this thread.

How long did you rehydrate for? My last batch I rehydrated (Nottingham) over an hour before pitching, and it looks like I should have only done for no longer than 30 minutes, after doing some research. I think that ideally I should have started the rehydration after I started the cooldown of the wort.

I started hydrating about 5 minutes before flameout and the chilling of the wort took about 20 more.. I guess about 30 minutes total before it was pitched.

I uploaded the video to youtube but it's still processing. I'll give you the short and sweet first....
At a moderate gravity and recommended dry yeast pitch of 1 gram per gallon:
1. Rehydration reduces lag but doesn't affect the FG.
2. Pure O2 increases lag but does not affect the FG. However, with the lag, it catches up in about 32 hours.

[YOUTUBE]vOrfmzpDmPk[/YOUTUBE]

Great stuff thanks!

Bobby, your series of video kicks ass. Thanks for all the work!

Now, would I be correct to assume that, in the end, any combination of O2 + Rehydrating yeilds the same results.

It appears as if the various tests each have benefits for different reasons. Rehydrating WITHOUT O2 starts fermentation quicker which seems like it might be beneficial if you have a high rate of infection - let the alcohol content create resistance.

The additional lag time could, theoretically, be offset by brewing up starters to get to a large enough colony size prior to pitching. This would pretty muc defaut the purpose of using dry yeast, but this information could be invaluable to brewers in different siuations.

Anybody get a different take on the results?

Once again Bobby, thanks a TON!

/me loves yeast

I'm not going for any conclusions till I hear a report on taste! Perhaps the longer fermentations lead to better tasting brew? BobbyM, are you bottling these suckers for a taste test in a month?

Really nice job! What was the SG of the wort?

Awesome job, Bobby

Another nice experiment and video, Bobby!

Thank you very much Bobby, that was a fantastic video!

Matt

Absolutely awesome, thanks! Your video will serve as a great reference to show the benefits of rehydrating dry yeast, a step so easily (and often) skipped, despite being really easy.

I was surprised at how significant the difference was between the control and the rest of the samples - the faster fermentation I expected, but the significant difference in FG was rather surprising. I figured there'd be a bit of difference, but I would have thought the rest of the samples would have caught up a bit more given enough time. So, I think your video will also serve as a great reference as to why you should pitch a lot of yeast! (suddenly my 1L starter flask seems small, especially in light of my recent issues with poor attenuation... time for a new toy!)

I realized it might be hard to comprehend some of the tables as the video is running so here are the tables:





12 hours - in case you can't read it; Control, 02+wet, 02+dry, no O2 wet, no O2 dry.


20 hours

So based on this, which will you use in the future?

I agree, great stuff. I do have to interject one constructive criticism. These results can ONLY be applied to Danstar Windsor. These results cannot be extrapolated to any other dry yeast until we have shown 1.) repeatability and 2.) that the trend holds true with other dry strains. This beast of burden should not fall squarely on Bobby's shoulders, either. I think the video provides a great resource, like a lab notebook and now we could all repeat this if needed and present excel data similar to what he has done.

Gread job setting the standard, Bobby

Great vid/experiment Bobby!

One question:

Are you going to compare flavor? I ask because I was under the impression that oxygenation is intended to create a healthier environment for the yeast to begin fermentation in, as an oxy poor environment may cause the yeast to produce off flavors while reproducing prior to beginning fermentation. am I correct about this? If so, I would think that the most important factor would be taste?

Can you tell I have yet to acquire any type of oxygenation setup?

I'm highly in favor of having this experiment repeated by others both with the same conditions and with other variances. If I get the ambition up again, I might try a higher gravity and slightly lower pitch rate to simulate a vile/propagator pack direct pitch.

I'm reluctant to try bottling the samples because I suspect all the sample taking may have introduced some oxidation. Maybe not. I suppose I can fill two bottles per sample and just drop 3/4 tsp of sugar into each bottle.

I'll try to have two tasting sessions in January where I can get a few local brewers to blind taste test and take notes.

Sea said:

Great vid/experiment Bobby!

One question:

Are you going to compare flavor? I ask because I was under the impression that oxygenation is intended to create a healthier environment for the yeast to begin fermentation in, as an oxy poor environment may cause the yeast to produce off flavors while reproducing prior to beginning fermentation. am I correct about this? If so, I would think that the most important factor would be taste?

Can you tell I have yet to acquire any type of oxygenation setup?

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As far as I can tell, the only reason to use oxygen is to get yeast to reproduce to grow the colony. Given an already high cell count in a rehydrated dry yeast pitch and a similar OG of 1.050 give or take, I don't think there will be any taste difference with O2 or not. Jamil Z has suggested that big slurry pitches will ferment a batch out just fine but will be missing some flavor profile that yeast growth imparts. I'm not so sure. Biermuncher mentioned his local brewery visit where they WAY overpitch and make really good beer in short time.

For now, if I brew something under 1.060 OG and plan to pitch dry yeast, I MAY skip the O2. One thing I will more aggressively disagree with is any suggestion that O2 "reduces lag time". It couldn't be further from the truth.

will be missing some flavor profile that yeast growth imparts

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This is only true for a few yeasts/styles. One of these days, I'll find my list.

Neutral yeasts work best in bunches. I agree about O2 increasing lag time, with more O2 the growth phase becomes longer. The higher population catches up eventually.