Sciencemadness Discussion Board

How is yeast dried so its viable when re-hydrated

wg48temp9 - 8-8-2020 at 13:05

I want to dry some yeast from my brewing so I can store it for the next time I brew.

I assumed I have to prepare the yeast in some way prior to drying or it will be killed. I have searched for a procedure but only found simple drying on a filter paper with out any preparation prior to drying.

Is that correct?

macckone - 8-8-2020 at 13:26

Commercially yeast are mostly freeze dried or sold as slants.
Different varieties are done differently so the exact process is strain dependent.
You can dry on a parchment paper for a lot of strains.
They won't be as active initially as commercial strains but will be fine within 24 hours.
If you use short ferment cycles you will likely be disappointed, if you prefer a longer fermentation then it should be fine.

B(a)P - 8-8-2020 at 13:28

That is a way to harvest it, but it is very difficult to keep everything sterile, since any temperature or sterilizing agent will likely also harm the yeast. If possible for you, it is best (easier) to store it wet. There are many procedures for wet harvesting online.

wg48temp9 - 8-8-2020 at 16:52

According to the reference below depending on the type of yeast and its growth conditions between 2+/-1% to 92+/-8% percent will be viable after freezing.

So freezing could kill 99% of the yeast before its even dried.

I guess drying with out suitable preparation could also kill the majority of the yeast. I did find a few home brewing/baking sites that claimed glycerol can be used as cryopreservative but i suspect they are not reliable sources.

I don't want wet storage. The yeast I am presently using was from a packet of dried yeast I had for at least 2 years. I quick test of some of the yeast in a half a cup of warm water and sugar and in half an hour it was almost frothing out of the cup. I don't think it could do that if it was 99% dead.


Attachment: yeast-Effect_of_Growth_Conditions_and_Trehalose_Content_.pdf (1.4MB)
This file has been downloaded 463 times

Sulaiman - 8-8-2020 at 19:53

I have no idea how to preserve yeast,
but on the assumption that you (like me) have been going for high %ABV for distillation
(ethanol for anti-covid hand steriliser)
you may find that the yeast at the bottom of your fermentation is mostly dead :(
So test the activity before considering preservation.

Dead yeast is logically reported to be a good (but not complete) nutrient for live yeast.
I've not tried yet
(still experimenting with tomato paste, DAP, pH, temperature, minerals, oils and vitamins etc.)
I am very very far from mastering this art - soo many variables.
(and the huge handicap of not being able to taste-test)

wg48temp9 - 8-8-2020 at 22:02

I used DAP (level teaspoon) and a one a day multivitamin tablet (for minerals and perhaps vitamins) with 4kg sugar and 20l of water and bakers yeast. Air temperature between 10C to 25C.

I have now purchased a packet of turbo yeast that claims to come with DAP and vitamins. Apparently the yeast may need a little oxygen for best growth, some brewers bubble in a little air at the start of fermentation. That's risky as lots of other microbes will be able to grow.

As the turbo yeast is about £5 a packet I would like a method to preserve it dry after I have used it.

I have also read that dead yeast is ideal food for new yeast but that confuses me as apparently yeast does not have the enzymes to utilise proteins.

UC235 - 9-8-2020 at 04:39

Quote: Originally posted by wg48temp9  
I did find a few home brewing/baking sites that claimed glycerol can be used as cryopreservative but i suspect they are not reliable sources.


Glycerol is used as a cryopreservative. But glycerol stocks are frozen and stored at -80C. They won't hold in a normal freezer

Metacelsus - 9-8-2020 at 17:33

Right, if you try to store it at –20°C you will be disappointed.

Commercial "dry active yeast" is often dried in spray drier or a fluidized bed system.

The use of trehalose as a protectant is potentially promising for amateur use. See this patent: https://patents.google.com/patent/US7052724B2/en

macckone - 9-8-2020 at 19:13

There is absolutely no way to get the same activity out of turbo yeast that is preserved by drying at home as when it is fresh out of the pack. Your best bet is to preserve it as slants (ie. wet live). The nutrient mixes are closely guarded secrets but they contain yeast hulls (dead yeast) and dap and a special mix of vitamins and minerals. If it is for drinking I would not use turbo yeast. I tried it at first and the results were meah at best. Slow wet cultured yeast are better. If you are trying to make fuel, hand sanitizer or lab alcohol, I had better results with mixed yeasts, start with a fast sugar resistant yeast that is good for a lower abv then add champagne yeast after the fast yeast starts to taper off. The champagne yeast will drive up the alcohol content and eat the dead yeast. This is also a good method for high proof rum as the lower abv yeast provides a better flavor profile.

wg48temp9 - 9-8-2020 at 22:36

Thanks for all the info guys.

Here is my yeast storage strategy. Without doing more research to generate a good dry storage procedure (>50% viability) that is potentially complicated and time consuming, the probability is that a simple dry storage procedure will probably kill up to 95% of my yeast. However that will only delay my next fermentation for a day or two as the yeast that is viable multiplies and the dead yeast will provide some nutrients (+ additions) for the viable yeast. I will also hedge my bets and prepare and maintain a wet culture in my fridge at least until I am confident the dry storage produces some viable yeast.

Provisional dry procedure: Filter or allow the brew to settle. Subject the yeast to heat shock to induce production of trehalose. Incubate the yeast with 50% glycerol solution. Filter out the yeast and dry. Finally store dry yeast in a sealed container in a freezer. Apparently the yeast should be in its stationary phase which I think means it has nothing to ferment. I assume that would be just prior to the dehydration with the glycerol.

I am hoping I can extract the yeast from a solution by filtration.

Tsjerk - 9-8-2020 at 22:47

Stationary phase means they came to rest, so they notice at some point nutrients are running low and they will go into hibernation.

There are roughly three phases; exponential, stationary and dying. When you make glycerol stocks, snap freeze in liquid nitrogen and store at -80 you can preserve the exponential phase. For other methods it is better to use the stationary phase, but it is not as simple as just removing the nutrients, they really have to go into this phase themselves.

There is also the lag phase, this is the phase between stationary cells getting new nutrients and the new exponential phase, this shows there are physiological changes made between the phases.

[Edited on 10-8-2020 by Tsjerk]

wg48temp9 - 14-8-2020 at 07:19

Two weeks ago I ordered an aquarium heater from China. It arrived today almost before the drive belt I ordered from a local company at the same time. I get lucky some times.
aqheater1.jpg - 2kB
I have decided to do my next fermentation using the settled yeast from my first one, which is about finished as there is almost no CO2 bubbling out. I will also add half the turbo yeast and keep the rest.

I will use the aquarium heater to keep the fermentation at the correct temperature now that the heat wave here is over.

I have found I can filter out the yeast using a fine glass filter though it is very slow.

My storage plan is now to create a new small fermentation and when the fermentation slows down I will put it in the fridge. The idea being the yeast will out compete other bugs and the alcohol will kill them or at least slow their growth. I expect to still have viable yeast after a month.

I will also try desiccating some stationary phase yeast. I assume after its been starved for a day or two it will be in a stationary phase.
I may try some slants if I can find some cheap agar.

PS: Something called "Agar Agar / Faluda Powder Vegan Vegetarian" is sold on ebay about £5 for 100g. Does anyone know if this is the agar used on slants?

Are there different types of agar?



[Edited on 8/14/2020 by wg48temp9]

macckone - 14-8-2020 at 08:27

Yes that is the agar used for slants.
You may need to add nutrient and some kind of sugar to keep yeast alive.
Some agars come with nutrient and sugar added already.
Yeast hulls and table sugar are good.
There are recipes on various brewing sites.

macckone - 14-8-2020 at 08:35

here is a method for malt agar which is for beer.
https://eurekabrewing.wordpress.com/2012/08/24/yeast-banking...

wg48temp9 - 14-8-2020 at 11:16

Thanks macckone.

I ordered some agar agar. Ebay £3.79 for 100g at 4% it should make 2.5l
medium more than I will use even if I use it in my Lupin germination experiments.

RedDwarf - 17-8-2020 at 02:54

Foodgrade agar agar is as good as the high priced bacteriological stuff:

Food-grade agar can be used as a low-cost substitute for bacteriological agar in the preparation of solid microbial media. No difference was observed in the colony morphology, growth rate, or viability of bacteria grown on solid media prepared using food-grade agar as compared with using bacteriological-grade agar. This simple tip can reduce the cost of the most common solid media by 80% or more.

Anal Biochem
. 2012 Oct 15;429(2):140-1. doi: 10.1016/j.ab.2012.07.011. Epub 2012 Jul 15

Tsjerk - 17-8-2020 at 05:57

The bacteriological-grade agar is made to do analysis on, for example LC-MS on secondary metabolites extracted from the agar. To just grow yeast the food grade stuff is of course fine.

4% agar is overkill, 2% is more than enough, you can probably use 1,5%... 1 % would be pushing it.

If you really want to go low budget you can also use gelatin, I don't know whether Saccharomyces produces gelatinases, but even if it does that shouldn't be to much of a problem as long as you don't want to streak in order to get single colonies.

wg48temp9 - 19-8-2020 at 12:44

Quote: Originally posted by Tsjerk  
The bacteriological-grade agar is made to do analysis on, for example LC-MS on secondary metabolites extracted from the agar. To just grow yeast the food grade stuff is of course fine.

4% agar is overkill, 2% is more than enough, you can probably use 1,5%... 1 % would be pushing it.

If you really want to go low budget you can also use gelatin, I don't know whether Saccharomyces produces gelatinases, but even if it does that shouldn't be to much of a problem as long as you don't want to streak in order to get single colonies.


Bacteriological-grade agar I would assume is equivalent a spectroscopicaly pure reagent or at least an AR grade reagent with about ten or more times the price.

I considered gelatin as I have some but I thought a different gel forming compound would also be useful for inorganic diffusion experiments and I have never played with agar or streaked. I suspect proteins may bind metal ions, hopefully agar will be better. It will also be useful to do microbe finger prints as a demo for my nephews of the importance of hand washing.

As 500g of agar was only about twice the price 100g I wanted to calculate the minimum volume of gel I could make with only 100g hence the 4%.

My agar agar arrived today only 4 days after my order. I will have to un-modify my pressure cooker and perhaps make an incubator from a microwave oven shell.

Thanks for the info guys.

PS The yeast is taking too many days to settle so I will attempt to filter out the yeast with a 1um mains water fiber filter.

PSS: I may be able to estimate the viability of the yeast with Methylene Blue. Apparently dead yeast is stained more strongly than the live yeast.





[Edited on 8/19/2020 by wg48temp9]

Tsjerk - 19-8-2020 at 13:31

The fingerprint on plate is a cool experiment! What we used to do was first one unwashed finger, then one after washing with water, then soap, then desinfectant and then one after going all out with desinfectant and brushes and all you could think off.

There usually wasn't much difference between the soap wash and the desinfectant wash nor the going all out. Although usually there were mostly only small yellow micrococcus colonies left, which is part of the normal bioflora of the skin.

wg48temp9 - 19-8-2020 at 13:45

Quote: Originally posted by Tsjerk  
The fingerprint on plate is a cool experiment! What we used to do was first one unwashed finger, then one after washing with water, then soap, then desinfectant and then one after going all out with desinfectant and brushes and all you could think off.

There usually wasn't much difference between the soap wash and the desinfectant wash nor the going all out. Although usually there were mostly only small yellow micrococcus colonies left, which is part of the normal bioflora of the skin.


I will not do the before and after washing prints as I am aware there may not be a significant difference, yes that is cheating on the demo but they need encouragement to wash their hands LOL

Tsjerk - 21-8-2020 at 08:40

I think there will definitely be a difference between washed and unwashed! There is only no difference between washed and thoroughly desinfected.

densest - 1-11-2020 at 20:59

"Yeast: The Practical Guide to Beer Fermentation" Chris White with Jamil Zainasheff, Brewers Publications 2010 www.brewersassociation.org
also anything from the author Fix (I don't remember his first name) They go into increasing levels of detail.

Yeasts mutate quickly if stressed so you want to treat them kindly. Mutated yeasts are rarely useful - they don't ferment correctly or produce nasty substances.

First figure out where the best yeast is in your fermenter. The viability and characteristics of the cells can be quite different from top to bottom and when in the cycle you sample.
If you want to keep yeast for up to, say, a month put a carefully prepared slurry in the refrigerator.
Beyond that things get more complicated. The books tell you what to do if you want to preserve the yeast without damage or mutation.
They describe what you need for a yeast lab.
If a packet costs 5 dollars/euros/pounds and you won't need it for 6 months, don't bother preserving what you have.

kveik yeast from Scandinavia has been bred/selected over centuries to survive and ferment in hot wort and when done scraped out and spread to dry.
That might be the simplest approach. Dunno if it would do what you want.