Useless Dry Yeast Facts #374

[pdilley]

Cake yeast was the original domestic yeast, moist, mushroom-colored, clay-like in texture and reasonably perishable. Its what our mothers and grandmothers used.

Active dry yeast is live yeast thats been dried, a process that kills up to 70 percent of the yeast cells. These dead cells surround the live cells, acting as a cocoon to protect them. For this reason, you must proof active dry yeast dissolve it in water, to expose the live cells.

Instant yeast is also live yeast, but its been dried at a much lower temperature, and using a different process. Only about 30 percent of the cells are dead, and therefore it begins to work much faster than active dry yeast (though active dry yeast will eventually catch up over the course of several hours fermentation).

What makes yeast misbehave? There are a couple of potential explanations for whats happening when yeast doesnt produce the desired effect. The first is pretty easy. In spite of the fact that yeast is newly purchased, it may not have been stored or rotated correctly prior to your purchasing it so that it isnt, in fact, as new as you think it is. A vacuum-sealed bag of yeast stored at room temperature will remain fresh indefinitely. Once the seal is broken, it should go into the freezer for optimum shelf life. A vacuum-sealed bag of yeast stored at high temperatures, howevere.g., in a hot kitchen over the summer, or in a hot warehouse before deliverywill fairly quickly lose its effectiveness. After awhile, if stored improperly, yeast cells will slowly become inactive (die). If you arent using your yeast fairly quickly (or even if you are), its a good idea to keep it in an airtight container in the freezer. It will keep for quite long periods of time that way (years in the freezer, if your freezer isnt self-defrosting).

The second reason may be this: When new yeast is dried after production, theres a certain mortality among yeast cells. Regular active dry yeast contains a much higher percentage of inactive (dead) yeast cells than does instant yeast. If youve been using instant yeast and have gone back to active dry, you may feel that the yeast is slow, when in fact its just acting as active dry normally does.

 

[Fermented]

I thought yeasts and freezers didn't mix owing to the cellular membrane rupturing on thawing... or am I mistaken?

Cheers - Fermented.

 

[razz]

You have to mix it with Glycerol or something similar ted.

 

[Bribie G]

I accidentally froze a medical pee jar of US-05 yeast cake the other day. I just popped it into the freezer after harvesting 'for ten minutes' to put it to sleep then intended to put in the door of the brew fridge for use next week - it had come out of primary yeast cake and probably still a bit of residual activity there. This morning I opened the freezer and there it was. Put it in the brew fridge and I'll do a starter with it next week and see what happens.

Will bump and report.

 

[Tony M]

You murder the yeast if you try and freeze it hydrated. The dried yeast that pete is referring to has no water in it to freeze so nothing to blow up the cell with expanding ice.
This is handy info from Pete. I once bought a large container of bread yeast which worked great for a couple of weeks then my loaves got smaller and smaller so I turfed the remainder of yeast and bought another which I kept frozen. My bread now stands tall right to the end of the yeast.

 

[white.grant]

So we are in fact talking about bread yeast? I've not heard anyone recommend freezing brewing yeast before.

cheers

grant

 

[Screwtop]

More confusing info for newbs.

Some facts:

Making Dried Yeast
I spoke with Bruce Patterson of the Lesaffre Group (producers of Fermentis dried yeast) about how dried yeast is manufactured.

Fermentis yeast strains are stored in a laboratory either at -80 C (-112 F) in glycerol or at 4 C (39 F) on slants. Each strain is genetically identified before it is sent to the factory for a production run. The yeast is transferred to a liquid media made from molasses (with a sucrose content of 4555%) with added nutrients to supply nitrogen, phosphorous, vitamins and minerals. The culture is stepped up several times in the lab before being sent to the factory.

At the yeast plant, the culture enters a rapid cell production phase and the yeast are fed continuously with molasses, nutrients and oxygen. The yeast are grown in very large fermenters, much larger than at liquid yeast plants. (How big exactly is a trade secret.)

Next, the rate of cell division is slowed and, in preparation for drying, nutrients and unspecified agents are added to the yeast to help it survive the process. The yeast cells are then harvested, separated from their media and dried to a cream with between 15 and 20% solids. The cream is pressed into a cake and extruded through a mold to produce yeast noodles. The noodles are then dried in an air lift dryer.

In an air lift, the yeast sit on a grate and hot air is forced up through the yeast noodles. The yeast are churned sort of like corn kernels in a hot air popper. (An older way of drying the yeast is to put the yeast in trays and have it ride on a conveyer belt through a long oven.) The yeast are slowly dried until they contain 94% solids. The dried yeast is then vacuum packed into sachets, which have a shelf life of two years when stored under 10 C (50 F). The viability of the dried yeast is 86%, but each dried yeast packet contains about 10 billion living cells per gram. Thus an 11 g pouch would contain about 110 billion cells. (These are the numbers for Fermentis yeast. The numbers for Danstar Nottingham and Windsor yeasts are comparable.)

Dried yeast companies report a very low contamination rate. (Fermentis yeast, for example, reports less than 5 bacterial cells/mL of wort in adequately pitched wort.) Patterson, however, mentions that sometimes the level falls below what can be detected in the lab. And, the experience of many brewers shows that this level does not result in problematic beer.

Cheers,

Screwy

 

[technocat]

Interesting read Screwy I guess if I live to be a 1000 years old I would never fully know what goes on in brewing.

 

[Ross]

Just to confirm....

Yes - Dried yeast can be kept refridgerated or frozen.

Cheers Ross

 

[pdilley]

Just to confirm everyones assumption. This is about dry yeast. In a dried state you can keep your dry yeasts viable longer by storing in the under some form of refrigerative state. The quick blurb at the beginning was just about cakes for a historical perspective but the title of the post focuses everything in general about dry form yeast).

Wet yeasts, yeast cakes, liquid yeasts have water in the cells and these will turn to ice crystals and burst/damage the cell walls when frozen.

I have not frozen liquid yeast before, but I would assume the glycerin plus a very slow cool down and freezing process would be best.

I have worked with fungi before at a mushroom farm but we would store agar plate cultures in sterile water in test tube slants. The non-nutrient base of sterile water forced the fungi into a dormant state where they could be kept for years at room temperature before being transfered to new agar plates. Its the same problems/techniques as with brewing yeast of trying to isolate strains and keep each strain as young as possible or in lab talk keep as close to Generation 1 or 2 as possible (Although we would count growth across one petri plate and transfer to a new plate or a grain master as a new generation).

Regarding "At the yeast plant, the culture enters a rapid cell production phase and the yeast are fed continuously with molasses, nutrients and oxygen. The yeast are grown in very large fermenters, much larger than at liquid yeast plants. (How big exactly is a trade secret.)" That is the same thing/process used, although primarily in the Chinese mushroom industry. Large liquid vats of fungal mycelium are continuously fed nutrients and create a "liquid slurry" that is used to inoculate grains or wood based growing medium.

The problem/benefit of most of the slurry techniques is you get multi-strain mycelial cultures. Its great as you know the stronger strains will outgrow the weaker strains and with all those strains you know you'll get quite a few variations on enzymes so you will have your substrate broken down. The only downside is you have multiple strains Which only worries the western cultures where we like our lab methods and isolating and cataloguing individual strains to test vigor, fruiting, and storage for comparison against other catalogued strains.

Mother Nature, though is usually smarter and when dealing with a hostile environment knows that multi-strain cultures win out in the end over mono-culture strains.


Cheers,
Brewer Pete

 

[brettprevans]

Spillsmostofit used to freeze some of his yeast. not sure whether it was pure liquid or yeast cake, but it certainly a frozen liquid form. i wonder how he found it?

 

[SpillsMostOfIt]

Spillsmostofit used to freeze some of his yeast. not sure whether it was pure liquid or yeast cake, but it certainly a frozen liquid form. i wonder how he found it?

I refrigerated a lot of it, but the vast majority of my yeast got fat upstairs. Thirsty Boy gave me a couple of cultures he glycerol'd up and I've had them in my freezer ever since. However, since moving out into the wilds I've been reduced to using just dried yeast.