where to keep yeasts

AlcoMoo · Post by **AlcoMoo** » Friday Sep 08, 2006 4:56 pm

I just got some yeasts from the HBS and I noted that the guy took them out of the fridge. Should I be keeping in there until I'm ready to use them. The other HBS I visited didn't do this.

blandy · Post by **blandy** » Friday Sep 08, 2006 5:05 pm

lethaldog · Post by **lethaldog** » Friday Sep 08, 2006 5:09 pm

Deffinately, think of it logically- if a HBS, hopefully the ppl who know best take up fridge space with them there must be a reason, and there is, it keeps them fresh, just dont put em in the freezer

AlcoMoo · Post by **AlcoMoo** » Friday Sep 08, 2006 5:51 pm

Thanks chaps! I'll stick 'em in the fridge.

Cortez The Killer · Tuesday Sep 12, 2006 4:23 pm

My HBS has told me to put the yeast in the fridge

luke · Post by **luke** » Wednesday Sep 13, 2006 6:31 pm

lethaldog wrote:Deffinately, think of it logically- if a HBS, hopefully the ppl who know best take up fridge space with them there must be a reason, and there is, it keeps them fresh, just dont put em in the freezer

Why not the freezer???

DonMI6 · Post by **DonMI6** » Wednesday Sep 13, 2006 6:36 pm

My local HB guy keeps his loose sachets in a plastic box, only the liquid yeasts are refridgerated!

lethaldog · Post by **lethaldog** » Wednesday Sep 13, 2006 6:40 pm

luke wrote:
lethaldog wrote:Deffinately, think of it logically- if a HBS, hopefully the ppl who know best take up fridge space with them there must be a reason, and there is, it keeps them fresh, just dont put em in the freezer

Why not the freezer???

Freezing yeast kills it

chris. · Post by **chris.** » Wednesday Sep 13, 2006 11:15 pm

lethaldog wrote:
luke wrote:
lethaldog wrote:Deffinately, think of it logically- if a HBS, hopefully the ppl who know best take up fridge space with them there must be a reason, and there is, it keeps them fresh, just dont put em in the freezer

Why not the freezer???
Freezing yeast kills it

I don't mean to be an ass but interestingly I have heard that a certain % of a packet of dried yeast can survive freezing due to the low moisture content. Of course it's not the wisest of way's to store dry yeast. The fridge works for me.

gregb · Post by **gregb** » Thursday Sep 14, 2006 6:43 am

The freezing kills the yeast by the liquid in the cell crystalising when it freezes and breaks open the cell. So I'd be inclined to agree with chris. about dry yeast, but for me I'll leave it in the fridge.

Cheers,
Greg

drtom · Post by **drtom** » Thursday Sep 14, 2006 6:57 am

I keep dried yeast for bread in the freezer and it seems to be fine. I suspect that the initial freezing process kills some cells, but those that do remain viable will do so for longer.

I would expect that the same would apply to beer yeasts with the proviso that beer yeasts (particularly lager yeasts) seem to be more sensitive than bread yeasts.

T.

50% Mogman · Post by **50% Mogman** » Thursday Sep 14, 2006 7:18 am

This is a good site about yeast freezing......
http://www.schwedhelm.net/brew/yeast_harv_freeze.html

I freeze liquid yeasts, and fire them up again.
Usually two starters required.

It don't cost much to experiment.

Have fun.............

blandy · Post by **blandy** » Thursday Sep 14, 2006 8:27 am

My microbiologist uncle seemed to think that freezing yeast would kill some but not all of it. He reckoned about 50% of it would survive. not too bad if you started wit a lot and then made a starter.

drtom · Post by **drtom** » Thursday Sep 14, 2006 9:04 am

If you're using dry yeast, you're generally overpitching anyway. The number of cells in a 7g sachet of yeast is a lot more than you would usually pitch from a liquid yeast starter. Killing of a few (even half) is unlikely to be a problem.

If you're using liquid yeast, or harvesting from your fermenter (something I haven't tried yet), then its a different matter - freezing liquid yeast harder on the yeast (cf previous reference to ice crystals).

T.

Beerpig · Post by **Beerpig** » Thursday Sep 14, 2006 9:30 am

A question for the chemistry minded

How is yeast dried?

If it is exposed to heat to do this, would it not mean that dried yeast can easily handle not being refrigerated?

Cheers

drtom · Post by **drtom** » Thursday Sep 14, 2006 9:41 am

I don't know for sure, but probably using low pressure evaporation.

If you make a [partial] vacuum, water will evaporate more readily at the same temperature. Chemists do this all the time in a thing called a rotary evaporator. I don't know for sure, but I would expect that the yeast microbiologists do something similar. It's actually a slightly different angle on the same process that makes freeze-drying work. It's 15 years since I did chemistry at Melbourne Uni, and I rather suspect some of the other guys here are doing it currently, or have done it more recently than I. I'm sure they can explain it in more detail if you want. I expect they'll go on about partial pressures and phase transition diagrams, and stuff like that.

T.

Dogger Dan · Post by **Dogger Dan** » Thursday Sep 14, 2006 10:33 am

Yeast is dried while it is active, which is why it doesn't need a starter per say but does need to be rehydrated.

Freezing will kill it, any moisture in the cells (it still has moisture) will rupture the cell walls and then promote decompartmentalisation (now that is a big word eh?)

The 7 g packs of yeast under the lid are crap, they need to be stepped up to at least 15 g to make a good brew. In some cases, the yeast needs to be pitched at a ratio of 1 g per litre to get things going.

Dogger

Beerpig · Post by **Beerpig** » Thursday Sep 14, 2006 10:53 am

Welcome back Dogger

So being a food science guru ................ refidgerate dried yeast ................. yes or no?

Cheers

drtom · Post by **drtom** » Thursday Sep 14, 2006 11:03 am

Is the 1g/L ratio for dry yeast or liquid yeast? I'm sure I've read that the number of cells per gram of dry yeast is much higher. I forget how many orders of magnitute, but I think it was a couple.

You're right about the under-the-lid packets, it was a braino - of course I had the safale, etc sachets in mind - are they 11g or 15g - whatever.

T.