Yeast starter

[paque]

Hi,

I did a starter on Monday evening...I put it in the fridge Wednesday evening. How long can the starter stay in the fridge without affecting yeast cells health?

 

[maffewl]

The refrigerator will help prolong the yeast life, but essentially the moment they are done with the work, their viability goes down in a non-linear fashion approximately 20% per month.

 

[eadavis80]

Northern Brewer told me a starter can "chill" in the fridge for up to a week and be totally fine. Just warm to room temp before pitching.

 

[brewkinger]

Northern Brewer told me a starter can "chill" in the fridge for up to a week and be totally fine. Just warm to room temp before pitching.

And they are correct.

20% viability loss per month equates to about 5% per week.

I have had starters that chill for a week or two before use. The caveat is that the number of viable cells before chilling (for me) is usually such that I can afford to lose a few billion and still have enough to do the job.

 

[rhys333]

Just as an indicator of how flexible yeast really is, I have direct-pitched 7 week old refrigerated slurry without problem. Initial lag time increased by a few hours, but fermentation was healthy and the beer tasted great. Not something to do on a regular basis of course, but you'll be fine with just a few days in the fridge.

 

[ACbrewer]

The refrigerator will help prolong the yeast life, but essentially the moment they are done with the work, their viability goes down in a non-linear fashion approximately 20% per month.

Somewhere on here is a thread about this, the guy found that for his samples it was closer to 1% per month, not 20% - and yes he used the standard methods for counting yeast.

This leads to several thoughts
1. One guy doing even several yeast containers is still way less then statistically significant. aka anticdote, not data.
2. the number of 20% comes from somewhere but nobody has to my knowledge every said where, so is it out of thin air?
3. something something making money off yeast sales something...

Which getting back to OP's original question. Assuming 20% per month works out to about 5% per week, you should be fine. Many of us pitch the packs as they are which works, although is figured to be under... I'd brew and pitch and not worry about it.

 

[maffewl]

2. the number of 20% comes from somewhere but nobody has to my knowledge every said where, so is it out of thin air?

There is information all over this world wide tube of servers... this is from the first hit in the Google machine.

"Every day, you lose viability (Fig 1). Storing the yeast for a month, you already lost about 20% of the living yeast cells!" from https://eurekabrewing.wordpress.com/2012/11/18/yeast-basics-check-yeast-viability/

I would assume the number comes from experiments such as this and others. However, I would treat the number to be a rule of thumb, not coded fact for all situations.

 

[ACbrewer]

There is information all over this world wide tube of servers... this is from the first hit in the Google machine.

"Every day, you lose viability (Fig 1). Storing the yeast for a month, you already lost about 20% of the living yeast cells!" from https://eurekabrewing.wordpress.com/2012/11/18/yeast-basics-check-yeast-viability/

I would assume the number comes from experiments such as this and others. However, I would treat the number to be a rule of thumb, not coded fact for all situations.

You link kind of proves my point. It just parrots the point and links to mrmalty, which is assuming the 20% also. There isn't ever mentioned a journal reference of "here is the experiment that shows that refrigerated yeast loses viability at about 20% per month" in which a statistically large sample was used - that is something on the order of doing this across 1000 1L yeast cultures started at 1.040. "Well that seems pointless why would anyone do that"... well for science, the same reason Pasture did it (ok not entirely, he was also paid)... but some grad student somewhere could do this. -Heck Budweiser probably has given what Chris White said about them in YEAST

What if our yeast packs said "attenuation 70 to 75%" and "viability loss 15 to 17% per month"? each strain could be different. White's book YEAST is very good, although he doesn't touch on this specific issue. Which I assume is either received wisdom, or fundamental from some course he took and doesn't see the point of talking about it.

Additionally he talks about how fragile yeast is, and I have to wonder about bacteria which were here before mankind, before dinosaurs, probably before sharks are as 'fragile'... Ok, maybe specifically yeast haven't been, it has probably been around for several million or whenever grasses first developed.

Again for the OP it is a week and I think we all agree 1 week isn't a big deal, he made a starter and will be better off with it and a week old, than if he hadn't. But how long can you store the yeast for? If the goal is to pitch about 200 x10^9 cells (as a base) after two months, will you have about 140? or 198? big difference.
And not to get to random, but if the sample has say only 100 million cells instead of 100 billion, does the rate of viability lose change? can you keep 100 million cells for a few years? how long will the yeast go dormant for?

:shrug:
it may not matter, after all, to get beer right, you have to have the yeast right. Underpitching results in off flavors, and while over pitching is possible, it takes a lot more than most people pitch to do that. (depending on style, I've seen something like 2x to 10x what a proper pitch is) - and I suspect that is a wild guess also.