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First batch in conical & banana flavor in blonde

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  • First batch in conical & banana flavor in blonde

    Hello, I would like to ask more experienced brewers about one strange (strange to me) problem. In our small brewery we brew
    regularly blonde ale in open fermenting vessels. Now for the first time I brewed two batches in our new 6,3 bbl conical.
    Everything went well, the fermentation temperature was 65 F first two days and then two days ramping up to 72 F. This
    morning was the SG reading 1.018 (OG is 1.050), the taste was normal with no abnormal aromas. I have cooled the beer to 45 F,
    because I wanted collect some fresh yeast later afternoon for another newly brewed batch. At the evening I took once more one sample of the blonde ale and it tasted like banana shake .

    I know isoamyl acetate can be formed by high fermenting temperatures or by stressed yeast. Is there another reason, what can also cause this problem?
    The only thing I have done since morning was cooling the beer. I have maybe some ideas, where the potential problem can be,
    but it still doesn't make much sense to me.


    Here's first reason - cooling of the beer was too quick (from 72 F to 45 F) and the yeast was stressed. But this is the thing
    I had done formerly in open fermenting vessels many times with no problem.

    Second reason - our conical has two cooling zones, one lower in conus and one upper in cylinder. Temperature of our cooling
    water is 32 F (we're producing also lagers). By primary fermentation I closed the lower conus cooling part, because I was
    afraid, that the cooling water is too cool and can overcool the relatively thin conical volume of wort down there. Is it possible, that
    this part was on contrary overheated by the fermentation heat and then isoamyl acetate was formed?

    If anyone has some good suggestions, I'll be very grateful!

  • #2
    Just so I understand a few things. You are now using a 3bbl fermenter that has 2 jackets, one for the cone and one for the top part? You stopped cooling the cone portion after the second day of fermenting? SG of 1.018 was your target FG or you expected it to ferment down more still?

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    • #3
      Hi, the fermenter is cca 6,3 bbl (1000 liter) and yes, it has 2 jackets, one for the cone and one for the top part. The cone portion was stopped from the beginning, the first day of fermenting. I read some advices, that this is recommendend procedure, because otherwise the cone part can be overcooled during primary fermentation.

      Target FG is cca 1.012, I was expecting still little more fermentation from measured SG 1.018. I usually close all valves little before target FG, so the beer can naturally carbonate during the secondary fermentation.

      BUT! I may know the reason of the banana aroma! Probably. I already moved the beer into lagering tank for secondary fermentation and dismantled the fermentor (conical). I found out that the fermentors temperature probe was not properly calibrated. In the vessel was +2 F, so it means cca 74 C at the end of primary ferm. And in the middle portion where the probe is situated. It could be even more in the upper parts of vessel and maybe there - in the upper part - could be the isoamyl acetate formed. When we poured a sample in the morning from the lower part of the vessel, the banana flavour was'nt there. But then we cooled the whole vessel and maybe the banana flavoured yeast from the upper part of vessel descended through the whole volume of beer down and left the unpleasant flavour, which was then noticeable in the evening the same day. I know, it's a little bit wild theory based of my little knowledge, but I can't figure out any other reason.
      Last edited by Starwalker; 05-01-2020, 11:05 AM.

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