Does low inoculation rate stress the yeast?

[lokbot]

I'm playing around with "Homebrew Dad's Online Yeast Starter Calculator" and there is a section that shows inoculation rates are optimal between 25-100 million yeast per ml. I'm wondering if I pitch my yeast into a starter that is below this are there any risks besides contamination? I'm not to worried about contamination because I will be inoculating an autoclaved media through a sealing injection port and the vessel will have a .2 um pore size syringe filter for air exchange

 

[pricelessbrewing]

Not in the way you're thinking. It's just a good idea to have an appropriate inoculation rate in order to have good growth rate and minimize risk of growth of other microbes in the culture.

 

[brewerdoc]

I'm playing around with "Homebrew Dad's Online Yeast Starter Calculator" and there is a section that shows inoculation rates are optimal between 25-100 million yeast per ml. I'm wondering if I pitch my yeast into a starter that is below this are there any risks besides contamination? I'm not to worried about contamination because I will be inoculating an autoclaved media through a sealing injection port and the vessel will have a .2 um pore size syringe filter for air exchange

Not sure where this Home brew dad gets his data from but in my reading I have found several publications which may help guide on thinking on this topic.

• 
  Its known that lower inoculums have higher rates of diacetyl production (1)

• 
  Five different pitch rates were assessed and the conclusion of the paper to crudely paraphrase the paper was that the results demonstrated that most aspects of the yeast physiology and flavor balance are not significantly or negatively affected when the pitching rate is changed. (2)

• 
  This paper did have an improvement in flavor stability by increasing the rate of pitching yeasts however there are many limitations to this study. They aged the beer at 20 degrees Celsius and pitched much higher rates of yeasts than the previous beers. A possible take away from this article is if you plan on storing or fermenting at high temp then pitch rates may make a significant effect. (3)

• 
  What about high gravity beers you ask? Well this article looked just at that and found that "The optimal pitching rate in high gravity worts (12–16°P) was about 0.3 g/l wet weight (2.3 × 10^6 counted cells/ml) and per one percent of original wort gravity. In very high gravity worts (20–23°P) the corresponding figure was 0.4 g/l (2.9 × 10^6 cells/ml). Higher amounts of yeast did not improve the fermentation rate." (4)

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I hope this helps. Of note the second article if you look at the data seems to have a cutoff of where much less diacetyl was produced with a pitch rate somewhere between 20 to 40ppm. I'm not sure where he got his data to support those recs as above but I could not find any limiting my search to data published after 1985.


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1.


[*]Erten, H., Tanguler, H. and Cakiroz, H. (2007), The Effect of Pitching Rate on Fermentation and Flavour Compounds in High Gravity Brewing. Jnl Institute Brewing, 113: 75–79. doi: 10.1002/j.2050-0416.2007.tb00259.x

2.


[*]Verbelen P et al. Impact of pitchig rate on yeast fermentation performance and beer flavour. Applied microbial and cell physiology feb 2009 colume 82 issue 1 pp 155-167

3.


[*]Guido LF, Rodrigues PG, Rodrigues JA, Gonçalves CR, Barros AA. The impact of the physiological condition of the pitching yeast on beer flavour stability: an industrial approach. Food Chemistry. 2004;87:187-193.

4.


[*]Suthko, M.-L., Vilpola, A. and Linko, M. (1993), PITCHING RATE IN HIGH GRAVITY BREWING. Jnl Institute Brewing, 99: 341–346. doi: 10.1002/j.2050-0416.1993.tb01173.x




FYI I could not for the life of me figure out how to do a numbered list so that they don't all show up as number 1. Sorry the citations look so weird

 

[TheMadKing]

Brewerdocs sources (great finds btw) would indicate that a lower inoculation rate reduces the yeast's ability to stay metabolically active post-fermentation, since they were specifically looking at diacetyl production. So yes, in a beer, reduced inoculation rate will result in more diacatyl in the finished product.

The growth factor can stress yeast. I believe Jamil (Mr. Malty) recommends never exceeding a growth factor of 10x in a starter because the yeast cell walls are depleted to an unhealthy level by the amount of budding necessary to reach saturation.

 

[BrunDog]

Interesting. I thought I read that under pitching does stress yeast and cause more esters and/or undesireable flavors.

 

[pricelessbrewing]

Guys he's asking about yeast inoculation rate (cells into starters) and it's effects on growth rates and cell density, not the pitch rate into the beer.

@TheMadKing replied appropriately.

@brewerdoc while useful info, not all thatrelevant to yeast starter inoculation. Homebrewdad uses the growth formulas outlined by braukaisers (and verified by several labs and homebrewers, most were within a reasonable amount of margin of error). He says so on the webpage at the bottom.

@BrunDog That is correct, under pitching tends to produce greater esters and can stress the yeast.

 

[lokbot]

Thanks for the input guys. Just what I was looking for.

 

[DurtyChemist]

If you also look at the inoculation rate and compare it to the amount of new cells grown you'll see a trend. Homebrew dad says it isn't really worth pitching a starter under 25 or over 100 because you won't get as many new cells produced as if you pitched within the range.
Yeast also talks about it and making starter volumes. The takeaway there was there is a point where starters won't do what you want. A 1-2L starter with 100 billion cells is where you want to be for a large majority of brewing because of what the authors refer to as yeald factor and I believe they say you want to be around a 6-8 range.
Figure 5.5 in their book shows the various inoculation rates from a 0.5L starter to a 4L starter. 1 L is an innoculation rate of 100, 4L is 25 and their growth rates are 7.6 and 6.3 respectively. The number of doublings is 0.5 in the 1L and 1.8 in the 4L. A LOWER inoculation rate is better for growing more cells. A 5 gallon inoculation rate is 5 and the growth factor is 3.6 according to the authors.

 

[kombat]

FYI I could not for the life of me figure out how to do a numbered list so that they don't all show up as number 1. Sorry the citations look so weird

1. Just
2. Like
3. This

Use the (list=1) tag, instead of just the (list) tag. Obviously, substitute square brackets for parenthesis.

On-topic: Mr. Malty prescribes a pitching rate of 0.75 million cells/mL for ales, and 1.5 million cells/mL for lagers. Curiously, Wyeast prescribes wildly higher pitching rates, with the lowest (ales with OG below 1.060) at 6 million cells/mL, and the highest (high gravity lagers) at 24 million cells/mL. For 5 gallons of a 1.080 lager, that works out to 450 billion cells.

My rule of thumb is 4 billion cells per point of starting gravity, per 5 gallon batch, for ales. Double that for lagers.

EDIT: Whoops, just noticed Mr. Malty's (Jamil's) recommendation is per degree plato. That's why the numbers were so different. That makes much more sense.