Koji-activated beer

Discussion in 'General Brewing Discussions' started by Classic LL, Jun 2, 2017.

  1. Classic LL

    Classic LL New Member

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    Hi folks, I'm working on a hybrid beer - that mixes normal beer wort, with rice that's been inoculated with a koji starter. While the yeast (normal beer yeast) ferments the wort, the koji converts sugars and proteins in the rice to more fermentables / yeast food. It's an open fermentation (the koji needs oxygen to create sugar from the rice), with a closed secondary fermentation. Here's the recipe:

    https://www.brewersfriend.com/homebrew/recipe/view/463381/koji-activated-rice-ale
    (If you're reading the recipe substitute my koji rice where you see flaked rice - I needed a placeholder to estimate the color and alcohol %.)

    So, that's all fine and dandy - I just bottled my first test batch, and a few things are blowing my tiny mind:
    • Despite using no coloring grains, the beer is a rich amber, and extremely clear. The taste has a round, fruity middle, sandwiched between beer-like flavors. The flavor was expected, but not the color.
    • The final gravity is 0.996 (what?!) with a brix reading of 4.75%
    On the last point, I'm trying to parse out what exactly happened to my beer to get these results, and what my final ABV is. The calculator on this page:

    https://www.northernbrewer.com/learn/resources/refractometer-calculator/

    ..tells me 8.04%, which is far enough way from my expectations that I'm assuming I broke the calculator, that I vastly underestimated how much sugar the koji would produce, or that the koji went to town on all the unfermentables in the wort.

    Can anyone out there throw some context around the ABV? Because my wort had whole rice grains in it, I was unable to get an accurate OG - so I need to make the calc based on the current state of the beer.

    Thanks everyone!
    -lloyd
     
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  2. jmcnamara

    jmcnamara Well-Known Member

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    Since you said brix, are you using a refractometer? Those give slightly false reasons if alcohol is there

    And like you said, not knowing OG probably doesn't help with the calculations either
     
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  3. Classic LL

    Classic LL New Member

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    I did use a refractometer to get the brix reading and I do recognize that the method (above) used to derive the ABV probably has a large margin of error, but I've also never seen a FG reading that low on a beer.

    One option - wait to drink it and see how drunk it gets me.
     
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  4. jmcnamara

    jmcnamara Well-Known Member

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    I've heard saison yeast can get that low. I know that's not what you used, but maybe you just made a superfermentable wort?
     
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  5. Ozarks Mountain Brew

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    Im guessing the color came from the liquid malt cooking too long or almost scorching, I brew a good DME and rice, ive used flaked rice but it needs to be mashed, I have 2 going right now and the 4.95 is as expected see its up to you how you mash and for how long and the recipe calculator shows a 35% Efficiency reading on the rice, you could change that if you know your getting more and you really need to stay on one website or another and not mix calculators
     
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  6. Trialben

    Trialben Well-Known Member

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    I think the problem with this koji breaking down the carbohydrates in the rice and coverting them to sugar is your not going to get a stable SG or OG because it will continue to change gravity as this koji yeast do its thing. Is this koji a symbiotic co existance of bacteria and yeast? Like in kombucha or kafir milk.

    Did you set those koji yeast to work on the rice then mix this in with your cooled wort then add yeast and ferment. Maybe this koji broke down the carbohydrate chains further in the wort as well? Like adding amylase enzyme to the fermentor?

    Any off flavours? No acidity?

    Sounds cool would be great to see a picture.
     
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  7. Classic LL

    Classic LL New Member

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    Upping both the efficiency and the yeast attenuation to both above 95% actually gets me close to there readings I have (assuming that the Brix:FG ABV calc is close to correct). This wouldn't be a huge leap of logic, given what I understand about the way koji works.

    I guess what I'm trying to figure out is - do I have a low FG because the koji did nothing and I just ended up with a super light wort or do I have a low FG because the koji punch-danced it's way through every non-fermentable in the wort.
     
  8. KC

    KC Active Member

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  9. Classic LL

    Classic LL New Member

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    You are right that the gravity has been a moving target. Last week, when I transferred it to secondary - my gravity was at 1.007. I'm assuming it's mostly done at this point, as koji needs O2 to work (I had to open ferment). So, after a week in secondary and now in bottles, it should be going dormant.

    Koji is a fungus, used for making a bunch of different fermented products (e.g. sake, miso, garum). It produces amylase, protease, and lipase - so it can pretty break down any food stuff. In this case, I created a small starter culture of the spores on some rice over a few days, and then mixed that in with 2 lbs of rice on brew day and dropped it into the wort with the yeast.

    The flavor is beer, then a round fruit middle, capped by a faint saaz hop flavor. We'll see what it's like after it's carbonated.
     
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  10. Classic LL

    Classic LL New Member

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    That's the formula I've been looking for! 7.5% ... 'ish. Koji is a badass, after all. Thanks KC - you the man.
     

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