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Best pitch rates to produce a clean ale

Discussion in 'Homebrewing' started by mattbk, Feb 25, 2013.

  1. mattbk

    mattbk Savant (425) New York Dec 12, 2011

    I was reading Zymurgy this weekend. I noticed a response about some confusion over best pitch rates to increase (or decrease) isoamyl acetate ester production, which gives German/Belgian beers its characteristic banana character. The comment was that high pitch rates contribute to this flavor - since the yeast do not need to use the precursor (Acetyl COA) to grow, more esters are produced. This confusing point jived a bit from what I've researched concerning American breweries brewing Belgian styels; that is, some seem to pitch high, some seem to pitch low, at varying temps (some cold, some warm.)

    The larger question for me (right now anyway) is if this is true for esters in general. ie, if I wanted to produce a very clean ale, should I pitch a bit higher than normal or lower? Wyeasts site says:

    A low pitch rate can lead to:
    • Excess levels of diacetyl
    • Increase in higher/fusel alcohol formation
    • Increase in ester formation
    • Increase in volatile sulfur compounds
    • High terminal gravities
    • Stuck fermentations
    • Increased risk of infection
    High pitch rates can lead to:

    • Very low ester production
    • Very fast fermentations
    • Thin or lacking body/mouthfeel
    • Autolysis (Yeasty flavors due to lysing of cells)
    This sounds somewhat in contrast to what I am describing above. Any anecdotal or (even better) scientific theory as to why one is better than the other would be appreciated.
     
  2. Matt,

    You might be interested in the chart package entitled “The Meaning of Life According to Yeast”.

    There is a chart on Esters which states:

    · Flavors Fruity, banana, solvent, apples

    · Formed Fusel Alcohol combines with a Acetyl CoA Fatty Acid

    · Conditions that favor formation include;

    - Increase Temperature
    - Fusel Alcohol pre-cursers
    - Increase gravity
    - Increase trub
    - Contradictory information on cell growth effects
    - Decrease Oxygen

    · Examples include
    - Ethyl acetate Light fruity solvent
    - Phelylthyl acetate Roses, honey, Apple
    - Ethyl Caprylate Apple-like
    - Isoamyl acetate: Banana

    I think the item of most interest to you is the statement of: “Contradictory Information on cell growth effects”. My guess is that the effect of increased esters due to underpitching may be yeast strain dependent?

    The presentation is located here:http://www.bjcp.org/cep/WyeastYeastLife.pdf

    Cheers!
     
    kneary13 likes this.
  3. Cell count, temp, O2, fermentation pressure have all been talked about in ester production.

    Dr. Clayton Cone from Lallemand has said that higher pitch rates results in more esters. Others say the opposite. It depends.

    Find out what works for you. I have a Bitter that I over pitched to try and get more esters. I was making Bitter that was too clean in taste vs what I drink in London.
     
  4. yinzer

    yinzer Savant (395) Pennsylvania Nov 24, 2006

    As far as the first issue, I've heard that before (high pitch rates = high per-curser ester production) . WL said the same thing at a NHC conference.

    In general all the rest is style dependent. Bamforth has said that.

    My thoughts:
    Lets take WLP001, it's a pretty clean yeast so a high pitch rate might not create excess esters. But a Belgian yeast that normally does would act different.

    With WL007 and WL001, I've taken advice from the Yeast book and pitched high gravity beers >1.090 @ 1.4x the on-line calculator numbers and I don't feel that I've had any of the negatives listed above. I've been very happy with the alcohol flavors.

    So I'd take each yeast individually and pitch at the normal recommend rate, then adjust.
     
    mattbk likes this.

  5. “I have a Bitter that I over pitched to try and get more esters.”

    Jeff, did your ‘experiment’ result in increased esters? What strain of yeast did you use? Did you use this strain before where you under pitched (or medium pitched) so that you have a basis of comparison?

    Cheers!
     
  6. Have used wy-1469 for the same beer 3 times, at the recommended pitch rate. Last time was the mrmalty pitch rate and just air from pumping into the fermenter, which was better. This time was overpitch and just pumping in. Have not done underpitch, and if the beer is what I want, I probably won't underpitch.

    Edit - the overpitch idea came from the Neva Parker talk at the last NHC. She had the response that was in this Zymurgy that Matt saw.
     
  7. So, did the over pitch result in increased esters? Will you continue to over pitch 1469?

    Cheers!
     
  8. Forgot to clearly state that it is still in primary for a few more days, then I will give a taste.
     
  9. OK, please report back when you have formuated an opinion.

    Cheers!
     
  10. mattbk

    mattbk Savant (425) New York Dec 12, 2011

    Jack, thanks for the link.

    It is interesting to me that in the pitch/sensory test that for the alt/lager the participants preferred the over pitch, while for the 3068 they preferred the under pitch - even referring to "complex banana" - this seems to go against the over pitch argument for creation of esters.

    I think yinzer's got it right - start with nominal rates and adjust according to each strain.

    FYI - I am planning on making a Kolsch/pale ale style beer - well hopped though, so almost like a light, German pale ale - I'd like to try using 1450 and pitching at a low temp (say between 60-62) to create a very clean fermentation. My tendency was to slightly overpitch due to the lower temps, but this article through me for a bit of a loop. Thanks.
     
  11. yinzer

    yinzer Savant (395) Pennsylvania Nov 24, 2006

    If you have the book Yeast look on p.35, it has a section on esters. It lists things that promote yeast growth will also reduce acetyl-CoA. And a~CoA is needed for ester production. Pitching rates aren't the only thing that effects yeast growth.

    My take away is that that overall it's more than simply the pitch rate. Concentration of a~CoA, concentration of fusel alcohol and also some enzyme activity are the main factors.

    So higher aeration rates will promote yeast growth and result in lower ester levels, but higher the aeration rate the higher the fusels alcohols - which increase esters!?!? It's enough to drive a man to drink.

    I'll say just another example of it's the yeast/fermentation that makes beer. And why you need to be cognizant of all the factors and if you can - not cut corners.