Rehydrating Dry Yeast?

Everything I have heard (and the directions on dry yeast) say to re-hydrate. I know it has been mentioned many times on the brewstrong podcasts. Here is the How to Brew chapter on yeast/starters:

http://howtobrew.com/book/section-1/yeast/preparing-yeast-and-yeast-starters

I typically use liquid yeast, and I always make a starter. When I do use dry yeast I re-hydrate.
If you haven't already you should look into the yeast pitching calculators and make sure you are pitching the right amount.
http://www.mrmalty.com/calc/calc.html

 

Your approach has worked fine for me and, no doubt, countless others over tens of thousands of batches (only 100 or so of which were mine ). The fact that some of the manufacturers print those instructions on the packet seems to support the legitimacy of pitching dry.

This is one of the more highly debated topics in this forum. Those who argue most vehemently against pitching dry have likely never done it that way. Indeed, some are proud of the fact that they're making a blind recommendation. I've rehydrated a couple of times and didn't observe a negative impact on lag time, fermentation vigor, FG, or, most importantly, taste. Granted, I've never done an A-B comparison, but I've never felt the need to (others have, and the results have been much the same as my casual observation). Thus, I've abandoned the practice. I do create starters when I use liquid yeast - that's a whole different thing, despite what some seem to believe.

The consensus is that there's as much as a 50% kill rate on healthy yeast cells when it's pitched dry. That may or may not be true. If it's true, then evidently, there's plenty of viable cells left over to do the job (arguably, the healthiest cells in the packet ). My favorite analogy is that, if it takes 2 gallons of gas to make the round trip to work, then 5 gallons in the tank won't get you there any faster or more efficiently than 3. This assumes, of course, that there are no snags along the way, and that holds true for brewing, as well. My take on that caveat is that, if you run into a glitch for which you believe additional yeast is a solution, the beer is not likely to turn out like you planned, anyway.

Regarding pitching calculators, virtually all of the yeast marketed to homebrewers come in a size that is fully capable of fermenting a 5 gallon batch of a 'normal' gravity beer (<1.065-ish OG is my rule of thumb, though I've gone higher). Though, as I said, I'll routinely make a starter with liquid yeast, due to its more fragile nature when compared to dry.

That said, there's nothing wrong with rehydrating, even if only for peace of mind, which is a real thing. I would never advise against it. I just don't see the benefit of adding yet another, rather meticulous step to the brewing process (temperature, sanitation, etc.). It's not difficult, it's just one more variable with a low tolerance for errors. I also don't see a benefit to adding yet another stress point for a less experienced brewer. There are enough actual things to worry about.

 

Not rehydrating runs the risk of loosing viable cells. The sugar density of the wort puts a high osmotic pressure on the yeast cells. This is the wisdom that underlies the advice to rehydrate. I used to not rehydrate and now I do. Too many other things have changed about my fermentation process for me to draw any grand conclusions from my own data. And while there may be some one-off Brulosopher type experiments out there that purport to show one thing or the other, but until we see some grand consensus from dozens of well designed experiments, I'll just stick with what the yeast companies say, because they are the experts. They say to rehydrate for the reason I mentioned above. Except sometimes they say to just spinkle the yeast on the wort. Basically, you should do rehydrate if you don't feel it is too inconvenient or if you think you may be seeing poor results with not rehydrating.

 

Pick one method. Stick with it. Vigorously defend your process choice for the rest of your life.

 

Except that yeast are more like the engine than like gas. More cells: bigger engine, faster trip. Do you think the "extra" cells are sitting on the sidelines?

 

The same speed limits apply, regardless of engine size, so the drive time is unaffected by the size of the engine.

No, but they're all working a little less hard. At some point, hard work has consequences (commonly exploited with some Belgians). Evidently, a 50% kill rate doesn't significantly cross that threshold for most 'normal' beers.

 

But more cells (higher pitch rate) makes the fermentation go faster. So what is the speed limit of which you speak?

 

Not in my experience (see my earlier comment). And most 'experts' in the field (the guys who make money writing about this stuff and whose opinions we tend to value) agree that more cells, at some point, can produce 'flabby', less interesting beer. Though the 'sweet spot' is a mighty wide chasm, so that's not typically an issue if you don't get carried away.

I'll stipulate that the gas analogy is an imperfect one. But I think it illustrates my point pretty well.

 

Below is a post I copied from another forum which discusses the topic of whether to rehydrate yeast. It includes a link to hbd.

Why shouldn’t you pitch dry yeast? It's called osmosis. Wort has a high concentration of sugars and the dry cells have a hard time taking in the water. Also the wort will be under the optimal temperature range. So what happens is the yeast die. “Skipping hydration kills about half the cells pitched” (1). They are killed because there cell walls are damaged to the point where they rupture spilling their guts into the beer “Besides only having half as much yeast needed, the dead cells immediately begin to break down and affect the beer flavor” (1) . That statement is what tells me that while GreenKrusty’s observation (dead yeast as food) has merit, there are extenuating factors that trumps it. Yes, there are viable cells left. Cells that have weak cell walls. Healthy cells walls are important to regulating what passes in and out of the cell. Low viability can cause “Slow/stuck /incomplete fermentations””Declining/low viability” “Sulfur””autolysis” (2). A study made also suggested that dry yeast rehydrated in wort can cause a high degree of esters, acetaldehyde and “hot” alcohol character. (3)


(1)p.146 “Yeast, The practical guide to fermenting beer”
(2) p.279,281,273 “Yeast, The practical guide to fermenting beer”
(3) http://seanterrill.com/2011/07/29/dry-yeast-viability-take-two/

in general
http://www.hbd.org/hbd/archive/3301.html#3301-4

 

It turns out, people wearing white lab coats determined higher pitch rates ferment faster

http://onlinelibrary.wiley.com/doi/10.1002/j.2050-0416.2008.tb00317.x/epdf

ABSTRACT:
To improve the productivity of the beer fermentation process, several strategies can be adopted. One of these promising strategies could be the increase of suspended yeast cells in the reactor. Therefore, the fermentation characteristics of 11 lager yeast strains were studied in normal pitched worts (20 × 106 cells/ mL) (LD) and in worts with a four-fold higher pitching rate (HD). The fermentation rate was 2–4 times increased when high initial cell levels were used.

 

My experience is exactly the opposite. i.e. higher pitch rates result in shorter lag times and faster fermentations than lower pitch rates.

I agree with this. I don't advocate deliberate over-pitching, unless the brewer has a specific goal in mind.

 

But is that necessarily a good thing? And where would you draw the line? If 2x to 4x is 'better' (the paper doesn't say it's better, only that it's faster), then why not pitch 10x, 20x, or 40x as much yeast? You'll note that the authors also discuss some downsides to higher pitching rates, notably an increase in fusel alcohols, and a higher risk of diacetyl due to the "shorter residence times" of the yeast (the paper discusses accelerated fermentation as a goal). Also, the effects are not universal - they vary by yeast strain. I found the final sentence in the Conclusion most appropriate to this thread, and very much consistent with my thoughts on the subject: "the flavour profile still remains mainly determined by the applied yeast strain." IOW, in the context of this discussion, it's much ado about nothing.

As I said, I've never done an A-B comparison. I've never observed an apparent difference in lag time, but it always 'feels' about the same. As to faster fermentation, it's got three weeks to do the job. What's the rush?

I'm not going to debate theories, or even measurable realities that have no discernable impact on my beer. It's interesting, and there's something to be learned, but, in terms of tweaks to make it better or simply different in some predictable way, dry versus rehydrated is not where I'll focus my effort.

 

Meaningless anecdotal evidence I'm tossing in here for no reason other than I'm presently 'trapped' in a recliner with a napping infant laying on me:

I brewed 11 gallons of 1.058 wort. Split it and pitched 1.5L starter of wyeast 1968 into one half and a single, dry, package of S-04 into the other. Pitching temp 65F. Both fermentors received a comparable dose of O2 before pitching, and some agitation ~ 30 min later when I carried them down to my basement.

The S-04 half was bubbling away in half the time, even though the starter was fresh and the pack from which it was prepared had a mfg date of Dec 10.

Scientifically? There's plenty of good reasons to rehydrate. Practically speaking? Not so many.
This from a guy who 'wears a white lab coat' for a living - yet has at least a few ribbons (some blue) from batches made with dry S-04 sprinkled on top of frothy wort.) ymmv.

 

I didn't say faster is better. @mikehartigan said more yeast won't ferment faster than less yeast on account of some half baked gas tank analogy. I provided scientific evidence that contradicts that claim.

 

I generally rehydrate. It's good practice for the yeasts that need it.

That said, I poured my Mangrove Jack 07 yeast directly into the fermenter last night. I want to piss it off. I've yet to use it, but the 07 has a temperature range of 15F.... I pitched at 71F because I apparently don't get esters otherwise. I'm not optimistic for my Dry Stout. I'll post a follow-up on the Mangrove Jack yeast thread.

 

s-04 is a yeast that actually makes sense to under pitch depending on what you want to achieve.

 

Since we seem to be bringing up ‘white coat’ people, perhaps the below Q&A with Dr. Clayton Cone (formerly of Lallemand/Danstar) might be of interest to some.

From: Dan Listermann
Subject: Yeast Hydration, Infusion Mashing and England

My question to Dr. Cone regards yeast rehydration. All the packages of
yeast contain instructions for rehydration yet they all ferment just fine
without it. I have to believe that such a procedure may be theoretically
beneficial, however it would seem to be margionally usefull at least on a
homebrew scale.

I own a home brew shop and a very common phone call is the ” My beer is not
fermenting.” problem. I go through the list of potential causes ( plastic
bucket lid leaks, too cold, ect.) About twice a week the caller will
indicate that he rehydreated the yeast. This is a strong signal that the
yeast has been damaged and will need to be replaced. I have come to the
conclusion that, since rehydration is not necessary to ferment beer
properly and there is a strong chance that the yeast will be damaged in a
botched rehydration, it is not desirable to recommend such a proceedure.
Just how important is rehydration and is it worth the risk?

Dan Listermann dan at listermann.com 72723.1707 at compuserve.com



Dan,
I appreciate your dilemma It is a universal problem for those that market
Active Dry Yeast.

Let me give you some facts regarding rehydration and you can decide for
yourself where you want to compromise.

Every strain of yeast has its own optimum rehydration temperature. All of
them range between 95 F to 105F. Most of them closer to 105F. The dried
yeast cell wall is fragile and it is the first few minutes (possibly
seconds) of rehydration that the warm temperature is critical while it is
reconstituting its cell wall structure.

As you drop the initial temperature of the water from 95 to 85 or 75 or 65F
the yeast leached out more and more of its insides damaging the each cell.
The yeast viability also drops proportionally. At 95 – 105 F, there is
100% recovery of the viable dry yeast. At 60F, there can be as much as 60%
dead cells.

The water should be tap water with the normal amount of hardness present.
The hardness is essential for good recovery. 250 -500 ppm hardness is
ideal. This means that deionized or distilled water should not be used.
Ideally, the warm rehydration water should contain about 0.5 – 1.0% yeast
extract

For the initial few minutes (perhaps seconds) of rehydration, the yeast
cell wall cannot differentiate what passes through the wall. Toxic
materials like sprays, hops, SO2 and sugars in high levels, that the yeast
normally can selectively keep from passing through its cell wall rush right
in and seriously damage the cells. The moment that the cell wall is
properly reconstituted, the yeast can then regulate what goes in and out of
the cell. That is why we hesitate to recommend rehydration in wort or
must. Very dilute wort seems to be OK.

We recommend that the rehydrated yeast be added to the wort within 30
minutes. We have built into each cell a large amount of glycogen and
trehalose that give the yeast a burst of energy to kick off the growth
cycle when it is in the wort. It is quickly used up if the yeast is
rehydrated for more than 30 minutes. There is no damage done here if it is
not immediatly add to the wort. You just do not get the added benefit of
that sudden burst of energy. We also recommend that you attemperate the
rehydrated yeast to with in 15F of the wort before adding to the wort.
Warm yeast into a cold wort will cause many of the yeast to produce petite
mutants that will never grow or ferment properly and will cause them to
produce H2S. The attemperation can take place over a very brief period by
adding, in encrements, a small amount of the cooler wort to the rehydrated
yeast.

Many times we find that warm water is added to a very cold container that
drops the rehydrating water below the desired temperature.

Sometimes refrigerated, very cold, dry yeast is added directly to the warm
water with out giving it time to come to room temperature. The initial
water entering the cell is then cool.

How do many beer and wine makers have successful fermentations when they
ignore all the above? I believe that it is just a numbers game. Each gram
of Active Dry Yeast contains about 20 billion live yeast cells. If you
slightly damage the cells, they have a remarkable ability to recover in the
rich wort. If you kill 60% of the cell you still have 8 billion cells per
gram that can go on to do the job at a slower rate.

The manufacturer of Active Dry Beer Yeast would be remiss if they offered
rehydration instructions that were less than the very best that their data
indicated.

One very important factor that the distributor and beer maker should keep
in mind is that Active Dry Yeast is dormant or inactive and not inert, so
keep refrigerated at all times. Do not store in a tin roofed warehouse
that becomes an oven or on a window sill that gets equally hot.

Active Dry Yeast loses about 20% of its activity in a year when it is
stored at 75 F and only 4% when refrigerated.

The above overview of rehydration should tell you that there is a very best
way to rehydrate. It should also tell you where you are safe in adapting
the rehydration procedure to fit your clients.

Clayton Cone.

 

The re-hydration instructions for Fermentis yeast is 80F +/- 6F. Clayton Cone says this is less than optimal. Who should you trust? Regardless, someone needs to surrender their lab coat!