Understanding Dry Yeast Activity

I did a BIAB IPA on Sunday that had an OG of 1.059.

After reading much conflicting information rehydrating dry yeast, I just pitched the satchel of US-05 directly into the oxygenated wort.

I had krausen forming within 18 hours.

My questions:

What, if anything, does the evidence of activity (krausen) tell us about the pitch rate, health & viability of the yeast pitched?

Have there been studies done on the effectiveness of rehydrating vs. not?

Is there a noticeable difference in fermentation start time & activity of underpitched wiry vs wort with sufficient, viable yeast?

wherestheyeast said:

I did a BIAB IPA on Sunday that had an OG of 1.059.

After reading much conflicting information rehydrating dry yeast, I just pitched the satchel of US-05 directly into the oxygenated wort.

I had krausen forming within 18 hours.

My questions:

What, if anything, does the evidence of activity (krausen) tell us about the pitch rate, health & viability of the yeast pitched?

Have there been studies done on the effectiveness of rehydrating vs. not?

Is there a noticeable difference in fermentation start time & activity of underpitched wiry vs wort with sufficient, viable yeast?

Click to expand...

Krausen can be higher than normal with a good batch of viable yeast. If the Krausen shows up early, it may mean you had a healthier batch and pitch of yeast.

I am not aware of any studies and have done dry yeast pitching both ways with good outcomes with each.

Typically fermentation will start faster and with a healthier pitch rate

The way I understand it from the likes of John Palmer and Jamil Z is that in their dry state, yeast cannot control what penetrates their cell walls. This can result in more dead yeast cells. Re-hydrating in water allows them to close the gates. So, more alive yeast = less lag time. I haven't compared the sprinkle method, but many will tell you that they have more lag time.

I don't know of any published studies to back this up.

When I did my first batch, I just sprinkled it on for lack of knowing any better and it was bubbling away within 18 hours, so I did the same with my next batch figuring it'd be fine and I had no problems once again. Despite that though, I do plan on properly rehydrating my next batch. First off, I want to see if it leads to more activity. I haven't needed a blowoff yet, so I'm curious if I will if I rehydrate.

I also plan on eventually getting into liquid yeasts and washing my own yeast, so I figure I could at least follow the dry yeasts instructions and rehydrate. That said, it's good to know if your in a jam that just sprinkling it on will work.

One thing though, is just because the yeast is active and working away that it's optimal just to sprinkle. If you can rehydrate, why not do it? Things may work if you don't, but why not give the yeast their best chance? Thats my thinking going forward anyway.

Well, anecdotal and meaning nothing but I've always had much better and faster and more visible fermentation just sprinkling. Every time I rehydrated I've had less and slower and far less active fermentation. But either way I got beer.

But that's absolutely nothing verifiable and completely anecdotal.

No, studies, eh? I'm a little surprised. Considering the adamance of opinion I'd have thought there'd be a bit more to go on. I mean, people getting headstrong opinion based on something they heard with no empirical evidence is surely a very rare thing, isn't it?

Rehydrating dried yeast should bring the yeast out of dormancy quickly and -- for the reasons two_hearted gives above -- in a healthier state than when they are sprinkled on wort. It is easy, however, to undo all the benefits of rehydration by heat shocking the yeast when you pitch.
If you take the rehydrated yeast, still around 100 °F, and pitch them into 70 °F wort, the 30 °F temperature swing will stun the yeast. After rehydration is complete, slowly acclimate the yeast by adding small amounts of wort to the rehydrated slurry and gradually bringing the yeast's temperature down to near the wort's temperature before pitching.

Chris Colby
Editor
beerandwinejournal.com

Thanks for the responses!

And a special thanks to Chris Colby -- I've enjoyed your articles on homebrewing along with your appearances on Basic Brewing Radio. Best wishes with the new blog!

"Krausen can be higher than normal with a good batch of viable yeast. If the Krausen shows up early, it may mean you had a healthier batch and pitch of yeast."

This is my understanding - but what does "early" mean with regard to the finished beer?

So, does my current experience indicate that rehydrating wouldn't have been necessary? If I did rehydrate would fermentation starter quicker? If fermentation started +12 hours after pitching vs. +18 hours after pitching, what effect would this have on the finished product?

Im not sure it would lead to a faster krausen, but it would let those yeast cells reproduce and do their thing more efficiently, because as two_hearted mentioned, it deals with the cell walls and things moving thru them.

At least that's how I've taken it by reading Jamil/White's book.

My personal belief it that re-hydrating dry yeast is better.

I have both sprinkled on the yeast and pitched re-hydrated. I have experienced that the re-hydrated starts fermenting a little bit quicker but even the dry usually starts for me in 6-10 hours.

As far as the finished product, I cannot tell the difference.

I'm a sprinkler and have never had any problems, especially with US05, always going within 12 hrs. There's been a great deal of discussion on this, and I believe one yeast company says rehydrate and one doesn't. Brewers choice whichever works for you, but you'll get beer either way.

Shortened lag time or vigor of fermentation isn't a great indication of proper pitch rate or health of yeast. An the other hand long lag time is an indication of an issue.....

A good experiment would be to brew a batch split and pitch half with sprinkled US 05 and the other half with rehydrated US 05. Equal weights in each batch of course and same storage temps. Hour by hour pictures and notes on fermentation and tasting notes.....good clean science.....I like it.

I haven't rehydrated dry yeast in over 10 years. I experimented with rehydration vs dry pitch on the commercial scale and concluded there was no appreciable difference in the finished product.

We always hear "if you don't rehydrate you will kill off cells!" Well, that is true, however the dead cells then become nutrient for the ones that weren't killed off... they get a kickstart, so to speak. The net result is pretty much a wash.

I don't know if this makes a difference or not, but it may be worth mentioning; I don't sprinkle. I put the yeast in the fermenter prior to adding the yeast. When the wort is knocked out to the fermenter (pumped into a unitank or dumped in to a plastic home fermenter) the yeast is immediately stirred up into a frothing solution. I see clear signs of fermentation in 6 to 8 hours consistently

Not bad I don't like the starter as that really isn't the question and you are changing the number of cells you are pitching with it.

Weak on science could be done better. Definitely the gist of what I am thinking though.

two_one_seven said:

Not bad I don't like the starter as that really isn't the question and you are changing the number of cells you are pitching with it.

Weak on science could be done better. Definitely the gist of what I am thinking though.

Click to expand...

I know what you mean, but it isn't my video and was the only one I could find right away! The vid I WAS looking for was flagged, presumably because the guy used some copyrighted music in it.

Since July of 2011 I have brewed 39 two gallon batches. Each time I pitch the yeast dry. Sometimes I use the whole pack, sometimes less. Never had a wurt that did not finish. Being in Hawai`i my pitching temp is usally in the low 80's and the fermenter is moved to the chest freezer to ferment at 65*. Had one or two blow off's. Shoots my cold water from the tap is only 77* so it's hard to get much lower than 80* even w/in the water around the boil pot.

What temperature should the wort be if adding the dry yeast without rehydration?

I'm not sure what it should be, but I usually get to 70ish before pitching.