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Underpitching=stressed Yeast- Is It A Fact?

Discussion in 'Yeast' started by Muscovy_333, 30/11/11.

 

  1. Muscovy_333

    Well-Known Member

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    Posted 30/11/11
    Hi Guys,

    Looking for some evidence to support that yeasties get stressed from under-pitching.
    A lot of brewers suggest it is a reason for funky flavours etc.

    I understand that temp fluctuations could impact and stress yeast, having to move from a growth phase back to a sleepy phase etc. It makes sense that sanitation/competition with other microbes could impact and stress. Same for funky water quality or pH.

    But under-pitching, I have not been able to find any evidence other than here-say.

    Can someone please direct me to some valid research or a sound theory that i could look into?

    Ta

    Musc
     
  2. Steve@PMF82

    Simplicity is perfection

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    Posted 30/11/11
    A quick google search found these three for some light reading :blink: :unsure:
    The first one is a book - Yeast physiology and biotechnology By Graeme M. Walker

    Second 2 are journal articles on yeast pitching rates for ethanol production.
    Have fun reading them, i will just continue to go by my small experiences and the here say of others, that pitching the correct amount of fresh, healthy yeast makes all the difference in the final beer.

    http://books.google.com.au/books?id=8rR-6P...tes&f=false

    http://www.springerlink.com/content/vy5m55...57/fulltext.pdf

    http://www.hindawi.com/journals/jbb/2010/419586/

    Edit - forgot links, also the Institute of Brewing and Distilling is a good resource. http://www.scientificsocieties.org/jib/
    All you need to know about yeast - Blue book at top of list http://www.ibd.org.uk/learning/learning-re...2/reading-list/
     
  3. Muscovy_333

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    Posted 30/11/11

    And now i feel l have just been lazy...

    thanks



    Musc
     
  4. Steve@PMF82

    Simplicity is perfection

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    Posted 30/11/11

    Just downloaded the blue book on yeast from IBD, looks pretty crazy, prob contains all you need to know about yeast and lots lots more by the look of it.
    I edited in the link first post.
     
  5. Muscovy_333

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    Posted 1/12/11

    Thanks Heaps for your help BEER4U.
    Just read through your links and got closer to the answers i was looking for.

    In summary for anyone who was not sure (I'm probably the only NOOB)....this is my take on some credible literature:

    1. Yeast cells actually use chemical messages to communicate to each other (didn't think they were that smart). If they are underpitched it is possible that they will not get enough messages from their mates to get them started and continue cell division at an efficient rate.

    2. Some yeast have bacteriocidal activity i.e. some strains (not all-hence a huge area of biotechnology) produce chemicals that stress other bacterial strains (not all), thats when we refer to yeast out-competing other microbes... Whilst outcompeting they retain more CHO for their own consumption= better yields (more alcohol produced). Therefore the funky flavours some people speak of produced from underpitching may not in fact be the yeast, but the result of other microbes impact on flavour. which leads me to my last point..

    3. It is not necessarily the yeast (at low pitch rate) that is responsible for funky flavours but the by-products of other microbes that will co-exist during fermentation.

    In conclusion, in full support of here-say, underpitching is risky business....but it's not necessarily the yeast responsible for funky flavour, but more likely the lack of yeast to beat down the other microbes before they influence flavour development.
    I think i repeated myself....but thats for my benefit.
     
  6. stakka82

    Hoptimus Prime

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    Posted 4/12/11
    anecdotally, over time i have had 2 batches which had particularly strange tastes. not completely off tasting like infection, but notes of fruit that shouldnt be there, hard to explain.

    with both of those batches i was using old kit yeast. the first time was with a cascade draught kit from the brewery gift shop. it didnt look like they'd go through a lot of the kits there with a high volume of tourists, rather than potential local homebrewers. so im guessing the can may have sat there for a while.

    the second time was with a packet of kit yeast that had been sitting in my fridge for around 3 years. not sure how long it had hung around before that but it was old. used it a couple months ago with some other ingredient 'scraps' as a mid strength. when i pitched that, and the cascade, it took around 2-3 days to even get any visible fermentation activity. both display/ed a kind of fruity, licorice note which shouldnt be there, not disgusting but just wrong.

    i'd say the amont of viable yeast with each of those old packets would have been very low, so maybe that supports the under-pitching theory.
     
  7. MHB

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    Posted 4/12/11
    As in most things brewing there isn't a single right answer, in this case there are pro and cons to choosing various pitching rates. The commonly states rules are a compromise between the benefits and drawbacks of different pitch rates, somewhere between 0.5-1*10[sup]^6[/sup] cells/mL/[sup]o[/sup]P for Ale and 1-2*10[sup]^6[/sup] cells/mL/[sup]o[/sup]P for Lager will give good results. Each brewer will have to decide for themself what works best for them.

    Truth be told most home brewers way under pitch, anyone who thinks a packet of US-05 in a brew is getting close is in for a surprise

    Just as an exercise how much yeast should we pitch into a 23L of 1.050 wort?

    23l 23,000 ml, 1.050 12.5[sup]o[/sup]P, pitch rate 0.75million c/p/mL
    23,000*12.5*750,000 = 215,625,000,000 cells
    From the Safe website dry US-05 should have around 6X10[sup]^9[/sup] viable cells / g
    215,625,000,000/6X10[sup]^9[/sup] = 35.9g, at 11.5 / pack = 3.125 Packets
    1 packet in the same brew is only giving you 240,000 c/mL/[sup]o[/sup]P, less than a third of the recommended pitch rate.

    Before anyone accuses me of trying to up my yeast sales, this is a subject close to my heart; I have been taking a long hard look at my own brewing and am looking to improve the outcomes, I really believe the pitch rate is one area I can make improvements.

    Last week a new book arrived, the long awaited translation of "The Yeast in the Brewery" published by VLB Berlin, some quite startling reading; this page is a lift that looks at the question being asked.

    MHB
    yeast.jpg
     
  8. Steve@PMF82

    Simplicity is perfection

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    Posted 4/12/11
    NO thank you, that's an interesting summary.

    You being a food scientist and all probably makes it easier for you to read the info then make ends of it.
    I on the other hand need to read and re read several times before i even start being able to put it together in my own head for comprehension.

    :icon_cheers:

    Edit : good addition there from MHB thanks
     
  9. felten

    Homebrew Conjecturist

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    Posted 4/12/11
    Mr malty's website says there is 20 billion cells per gram, not 6 as per fermentis. So who do we believe? :p
     

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