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  • Hop utilisation problem

    Gday
    I realise that a similar post was issued previously, but am interested in something slightly different. Currently brewing two ale brews which result in roughly the same BU's analytically. The first uses 19AAU (2kg @9.5AAU) up front, whilst the second has about 88AAU (8kg @11AAU). The resulting BU is 38, and 44mg/l respectively. Both are relatively high gravity brews. The secong brew is our IPA, and I have tried everything to achieve BU's of about 50+, but cannot, instead having to relie on isomerised extracts to add the difference, which i don't like (flavour +don't believe it necessary). I'm wondering whether the kettle utilisation is declining rapidly due to the excessive amount of hops (8kg in 6000lts, compared to 2kg in same volume for the slightly lower brew), and whether anyone has any experience at what level achieves the highest utilisation before it starts to drop off.
    The second thing I am wondering is whether there is greater isomerisation occurring at the second hop addition (15mins to cast out) than i'm led to believe. The first brew has an addition of 5kg@9%aau, whilst the second one has 4kg@6%aau. After boil the wort is pumped into a whirlpool, so from hop addition to transfer into the fermentor is probably 15min + 20min (transfer) + 15min (whirlpool) stand = 50min to start of transfer to cellar, taking about 1hr to transfer 6000lts. But i was led to believe that isomerisation only occurred with steam distillation, i.e. on boil. The cast out hop additions are 7.5 kg @9% for the first and 3kg @6%aau for the second, being put in on transfer to the whirlpool. Again I didn't think this addition would result in much isomerisation, though the aroma component isn't as strong as I would have liked. Any ideas would be greatly appreciated, as I'm struggling to get the BU's i'd like and also the aroma component. I was contemplating putting the cast out hops into the whirlpool at the start of transfer to the cellar, but wasn't sure they would settle out due to no tangential motion. Much appreciate any help
    Thanks
    Andrew
    Andrew Morgan-Jones
    Brewer

  • #2
    In reference to the utilization of your second addition, it is not linear. You achieve greater utilization (isomerized alpha acid contribution relative to time in boil) during the earlier additions and then it falls off the longer you boil. Also, the greater the vegetal mass of hops in the kettle, the less utilization you will realize. I would suggest a (clean) higher alpha boiling hop to reduce the mass of hop matter in the kettle to get a more effecient bitterness, also think about first wort hopping. Another factor is how vigorous your kettle boil is, maybe you are "under powered" on BTU's?

    ...also, are you making subjective observation for IBU or is this lab? The malt bill, yeast strain, water chemistry,ect...will have play on subjective IBU.

    Hope this helps,
    Beaux

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    • #3
      Any ideas what your corresponding pH values are?

      If the wort pH of your IPA is lower (<5.0) it will inhibit isomerization as a higher wort pH results in higher utilization. If the OG's are very different it could also explain lower utilization for your IPA. Lastly, I would suggest using super alpha hops if trying to get 50+ IBU's in your IPA. It will get you there and reduce your trub load. Also...it is possible to get isomerization of hops post-boil (whirlpool additions) while getting some nice aroma compounds as well.
      Mike Jordan
      Brewmaster
      Boxing Cat Brewery
      Shanghai, P.R. China
      michael@boxingcatbrewery.com

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