Tag Archives: yeast

Rehydrating Dry Yeast with Dr. Clayton Cone

I came across this Q&A exchange between Dan Listermann and Dr. Clayton Cone regarding the proper rehydration of dry yeast and thought I would post it here. I haven’t had time to do any of the tests I want to do comparing dry yeast and liquid yeast, but I will certainly incorporate a comparison of rehydrated yeast and yeast sprinkled directly on the wort.

 

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 intering 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 looses 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.

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Dry Yeast v. Liquid Yeast

I’ve been messing around with brewing mead and wine recently in addition to my beer brewing activities. It’s a veritable 24 hour brewing circus around my house with any free minute filled with fermentation of some kind. At the moment my living room smells like a fermentation room at a winery. Stephanie loves that kind of thing.

Anyway, wine and mead makers tend to use dry yeast as opposed to beer makers who tend towards liquid yeast. Older style beer kits that come in a can still include a packet of dry yeast (or so I’ve been told, I’ve never actually made one), but most contemporary recipes call for liquid yeast from Wyeast or White Labs. From what I can tell, most serious brewers are using liquid yeast and making starters to pitch into their wort in order to get a proper yeast cell count for a clean fermentation. There are a few yeast pitching rate calculators out there from Wyeast and from Jamil and some well read articles that serve as the guidelines for making and using starters.

Standard brewing practice also involves either shaking the crap out of the carboy to aerate the wort or using an oxygen tank and diffusion stone to dissolve pure oxygen into the wort. Yeast use oxygen to make lipids/sterols for their cell membranes. Healthy cell walls allow for better yeast growth and propagation, better uptake of nutrients, and better alcohol tolerance. Healthier yeast means cleaner fermentations and fewer off flavors in the final beer. There has been a interesting series of posts from Mike Flaminio on wort oxygenation on the Homebrew Beer Blog recently as well. The aim there being consistent, proper wort oxygenation as opposed to the blind process most of us follow that apparently leads to inconsistent over oxygenation. There has also been a long thread on the Brew Board about using very small amounts of olive oil in the wort instead of oxygenating it. Yeast apparently can uses the olive oil to synthesize the lipids/sterols they needs for their cell walls.

Wine kits just ask the wine maker to sprinkle a packet of dry yeast on top of the must to start fermentation. Some wine makers rehydrate their yeast prior to pitching, usually in Go-Ferm. There seems to be some debate in the wine making community about which practice is preferable, with a larger number of people taking the wine kit makers advice (from my limited reading and experience). According to Tim Vandergrift at WinExpert, the leading wine kit manufacturer:

“The real scoop on why kit companies don’t ask you to rehydrate: It doesn’t make any difference.

In the 6 US gallon (23 litre) volume, the 5-gram packet of yeast provided will ensure a quick and thorough fermentation with a quick sprinkling and nothing else.

It is technically true that re-hydrating gives higher viable cell counts–but only if you do it with perfect precision and accuracy. While there are a couple of pitfalls, the commonest one is temperature shear.

Since you have to rehydrate at 100F, in ten times the weight of the yeast in pure water, the yeast slurry will be fairly warm. If you pitch this re-hydrated mass into a must of 64F, the shock of the wildly disparate temperatures will kill a lot of those previously viable yeast.

In tens of thousands of trials, we’ve never seen anything approaching sub-optimal times for culture strength and subsequent fermentation.”

In either case, there are no starters and no oxygenation occurring, though wine makers do sometimes stir their must and/or leave the fermentation chamber relatively open compared to brewers in order to get more oxygen dissolved. These are some pretty divergent practices, so I’d like to know how or why this is the case.

I found a response to questions about starters and oxygenations from Dr. Clayton Cone at Danstar/Lalleland/Lalvin, a leading manufacturer of dry yeast, that I found pretty interesting. Basically he says that dry yeast come packed with the amount of lipids needed to triple the yeast cell count. After those lipids have been used up, additional oxygenation is required for healthy cell growth. For brewing a 5 gallon beer between 3% and 5% alcohol, no additional yeast or oxygen are needed apart from what is available in a single 11g packet. For higher alcohol content beer, you either need to pitch additional yeast or oxygenate to allow for yeast growth. I’m not sure what Danstar considers a proper pitching rate, so that is something I will have to investigate. I do know that Jamil recommends pitching about 10g of yeast on average for an average gravity 5 gallon batch in Brewing Classic Styles. [Edited per Jamil’s comment. Thanks Jamil. And as Jamil notes, batch size, OG, and yeast type are all variable inputs in the proper pitching rate – use his calculator to get precise amounts- I do.]

As a brewer, I’d prefer a higher pitching rate for higher alcohol beers so that propagation was mostly complete at pitching instead of trying to grow the yeast in the wort. That way the yeast can spend their time fermenting while in my wort instead of growing.

Dr. Cone mentions that Danstar grows their yeast along a different metabolic pathway than the one used by brewers that uses basically no sugar. Yeast propagated this way create very little alcohol. I assume this is done because it allows for more efficient healthy yeast production. When growing yeast in a starter, “no matter how much air you feed the fermentation, alcohol + CO2 are the main by-products. Your starter culture will have a much higher level of sugar [than the culture used by Danstar]. You will produce some cell mass but mostly alcohol and CO2 no matter how much air you add by stirrer or bubbles.” So starters increase cell counts but not in a way that is as effective as the propagation method used by Danstar. I guess that this also means that yeast grown in a starter, even under ideal conditions for a starter, is of a smaller amount and of potentially of lower quality due to the presence of alcohol and other less than ideal conditions.

So I guess my question is whether making a starter is an effective way to increase yeast cell counts prior to pitching or if instead it’s just a way to get yeast into active fermentation prior to pitching. Perhaps they generally make alcohol and CO2 and that starters are not the ideal environment for propagation even with the proper amount of oxygen. Buying 2 vials of White Labs yeast or 2 Wyeast Smack Packs is prohibitively expensive, especially given the increased cost of malt and hops. So I understand why people look for ways to grow their own yeast. But dry yeast is relatively inexpensive and prepackaged with the lipids necessary for healthy propagation and fermentation. Pitching a packet of dry yeast that cost less than $2.00 is definitely cheaper than pitching a starter made from DME, yeast nutrient, and a $6+ liquid yeast product – and that doesn’t count in the cost of the equipment needed to make starters (flasks, stir plates, etc.) or the time involved. If the metabolic pathways used by yeast from a starter for propagation produce lower quality yeast than the yeast from dry packets, that makes using dry yeast even more appealing. And if re-hydrating dry yeast generally makes no difference, all the better.

Of course liquid yeast manufacturers make a far wider variety of yeasts than are available as dry yeasts, so sometimes your options are limited.

I’ve never used a dry brewer’s yeast, so this is all just speculation at this point. I’m planning on trying out some dry yeast and comparing the results to equivalent liquid yeast from starters. I ordered 12 packets of dry yeast, 2 each of 6 different varieties, from Williams Brewing mostly because they are having a sale on dry yeast – 25 cents off each packet of dry yeast when you buy 12 or more. We’ll see what happens, but I am hopeful that I’ll get good results. If dry yeast is a reasonable or better alternative to liquid yeast and starters, maybe more people will start using dry yeast and more varieties will be made available. Or it might suck and I’ll go back to liquid yeast starters.

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Making a Yeast Starter

I was planning on brewing this past Saturday, but it never happened. I used the weekend to put a new paving stone sidewalk from my back porch to the alley instead. It looks awesome, but it didn’t produce any beer. I do hope that it will make for a flatter surface for brewing in the future.

Anyway, I made a starter last Thursday for the beer that didn’t happen and took some pictures. I think I’ll use it this weekend.

I always make a 2L starter for my 5 gallon batches. Making starters was one of my early brewing improvements, and I think it has really improved the quality of my beer. I know lots of people use the yeast pitching rate calculator on www.mrmalty.com to calculate pitching rates (thanks Jamil from all of us for everything), but I just figure that a 2L starter is always going to be adequate for a 5 gallon batch. Maybe I’ll get more specific about my yeast counts in the future, but this works really well for me now.

First I take my yeast out of the fridge to warm up to room temperature. If it’s a Wyeast smack pack, I activate it. I then mix 2 cups of extra light DME with 1800 mL of water in a mixing bowl. No need to sanitize since everything is going to get boiled. DME has a tendency to clump up when it gets wet, so I use a whisk to break up any clumps and get the DME well dissolved. I’ve got some more stirring to do in this picture as you can see some DME clumps near the whisk. I also add some yeast nutrient according the manufacturer’s instructions.

I used to try to mix DME into the water in my 2L Erlenmeyer flask directly, but it’s nearly impossible with all the clumping. Adding the DME on top of the water creates a plug in the neck of the flask and adding the water on top of the DME leaves a cake stuck to the bottom of the flask that eventually burns when you try to boil it. I gave up on mixing in the flask pretty quickly.

When the DME is well dissolved, I pour the wort into the flask, add 1 or 2 drops of foam control, and stick it on the stove over medium heat. I boil the starter for 15 minutes. Foam control helps prevent boil over, which is extremely easy to have occur with the narrow neck of the Erlenmeyer flask. I used to have boil overs all the time when I made starters. It makes a huge sticky mess on the stove that is a pain to clean up. The starter for the milk stout I recently brewed was my first starter using foam control. I still had boil over problems. The foam control keeps the wort from foaming up, but it doesn’t prevent large bubbles from forcing hot wort out the top of the flask. The trick for me was to keep the stove on medium heat until the starter is about to boil, then turning down the heat to low for a 15 minute boil. You could also just leave the starter on low heat and wait for it to boil, but it takes forever and I like to tempt fate.

After the 15 minute boil I cover the top of the flask with a piece of foil while wearing an oven mitt. I take the flask to the kitchen sink for a cooling bath to bring the wort down to pitching temperature. To conserve ice, I first run cold water over the side of the flask, then move it to a bath of swirling cool water, and finally to a bath of swirling ice water. I’m always amazed that the flask doesn’t break from the temperature shock, but that is what it is made to do.

Once the starter is down to pitching temperature, I add the yeast and move the starter to my fermentation location. I always ferment my starters at the same temperature as I will ferment the beer for which it is intended.

After active fermentation subsides, I move the flask to the refrigerator. The yeast will drop to the bottom of the flask and form a nice solid yeast cake. When it’s time to brew, I decant off the liquid on top of the yeast and pitch only the yeast cake into the wort.

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