Starter size by numbers.. Not sure I get it.

[p_p]

Since day one in my short brewing career, I've took your advice to heart, got myself made a stir plate and made starters. Good.

Now, I am looking at that vast amount of guu at the bottom of the FV and wondering how big it appears to be compared to what I pitched. So to the numbers.

So I have a vial of yeast and I estimate it has 70b good cells. I make a 1.036 starter using 170g of extract.

According to Kai's formulas, I get 1.4b cells for each gram of extract so I end up with about 310b cells. That is accomplished in 2 generations and a bit more? I don't know how to calculate that...

Anyway, I understand this is a good healthy rate for 20 ltr of a 1.060 (14.7P) ale.

So in it goes, into this wort that has an equivalent of 3500 gr of extract. So, again, at 1.4b cells per gr, I will get at the end over 5000b cells. The final number was reached in 4+ generations.

Mmmmm, actually! that sounds right... now that I have written it down and kind of thought it through in the process, it does not sound that bad, I guess. 4 generations isn't that bad. Yeast won't be tired and damaged by then.


Ok, well, I've written the post already. No point deleting it now. Sorry :/

Cheers

 

[flars]

The yeast won't be tired or damaged at the end of the fermentation unless it was very high OG. You can harvest a whole bunch of healthy yeast.

I consider the harvested yeast 1st generation since the yeast only fully fermented a beer one time. I don't count buddings as a generation since this propagation occurred under ideal conditions with no stress.

 

[p_p]

The yeast won't be tired or damaged at the end of the fermentation unless it was very high OG. You can harvest a whole bunch of healthy yeast.

I consider the harvested yeast 1st generation since the yeast only fully fermented a beer one time. I don't count buddings as a generation since this propagation occurred under ideal conditions with no stress.

Thanks for your reply.. I wasn't expecting any after all that blabbing.

You mentioned that budding happened under ideal conditions with no stress. So at which point in the process you'd consider the yeast was subject to stress and therefore you'd choose to call it a new generation?

Is the projected exponential growth factor a number worth keeping and eye on in our brew sheets? Though admittedly it is factored in the way we calculate our pitch cell count ... I'd imagine the rates we've been told to use (eg 1m cells per ml per P for ales) are meant to give enough yeast budding to impart flavour but not too much as to avoid weak cells?

Should I buy the yeast book?

I will certainly go and find a recent post where a 1x 2lts starter was compared to a stepped 2x 1ltr option.

Thanks

 

[flars]

Thanks for your reply.. I wasn't expecting any after all that blabbing.

You mentioned that budding happened under ideal conditions with no stress. So at which point in the process you'd consider the yeast was subject to stress and therefore you'd choose to call it a new generation?

New cell propagation during the growth phase in the fermentor or in a starter wort ends when the alcohol content of the wort reaches about 3.5%. I don't count the number of times budding occurs in a starter wort as a generation. I call a yeast 1st generation when I harvest the yeast from the fermentor after the first time it has fully fermented a beer. When I use this harvested yeast to ferment a second beer, and then harvest, I call it 2nd generation yeast.

Yeast can be stressed by the fermentation of a very high gravity beer. I would not harvest yeast that fermented a high gravity beer. I will harvest from an over built starter to have the same/fresh yeast to brew with a second time. There are other yeast stressors such as poor temperature control of a fermentation. I won't harvest yeast from a bad or incomplete fermentation.

Is the projected exponential growth factor a number worth keeping and eye on in our brew sheets? Though admittedly it is factored in the way we calculate our pitch cell count ... I'd imagine the rates we've been told to use (eg 1m cells per ml per P for ales) are meant to give enough yeast budding to impart flavour but not too much as to avoid weak cells?

The growth factor expressed in a yeast starter calculator is for optimum utilization of the amount of DME used for the volume of the starter wort. A growth factor of less than one is basically a waste of DME and time making the starter for the number of new cells produced. This isn't a number to track. It is just for making an optimum starter to produce the number of new cells needed for the beer being brewed.

I have begun using 0.75 million cells / ml / degree plato for beers 1.065 OG or less for most styles of beer. For the beers I make it seems that a higher pitch rate does not make a better beer.

Should I buy the yeast book?

The yeast book is a good investment.

I will certainly go and find a recent post where a 1x 2lts starter was compared to a stepped 2x 1ltr option.

Thanks

These are two good yeast starter calculators with some good documentation.
http://www.brewersfriend.com/yeast-pitch-rate-and-starter-calculator/
http://www.brewunited.com/yeast_calculator.php

I try to understand the brewing process but also try to not over think it. Keeps brewing more fun rather than a study.