Extreme color change during fermentation
I'm looking for good information on color changes during fermentation. In general, I find most things lighten to some degree. There is some discussion on the web about protein coagulation and fall out taking out some color.
I brewed a cream ale using thai sweet red rice. The post-boil color was a lovely dark ruby red, which I was hoping would stay. Once it finished, it was a medium straw gold. It looked like all the color added from the rice was just gone. Precipitated out? nope. Yeast bed is normal color, trub is light, and the color should act more as a dye than a suspension.
I'm wondering if there are any plant dyes which essentially become yeast food. I can't find any research. Color contributed from malt, seems to stick around. Color from red rice, totally gone. A bit disappointed by the color change.
I think I found out why. Apparently what is labeled as red rice, is actually better known as Black rice. The pigment in black rice comes from Anthocyanin (think red cabbage). This is an indicator, so to test it, I boiled up some of the rice, and made some a little acidic and some a little basic. The color change is obvious.
So it turns out that anthocyanin is a glucoside which can be decomposed through fermentation. It would appear then, that brewing with black rice, or red cabbage (feel free to try) will not yield the desired results.
Interesting: Indican, which is a colorless glycoside, when fermented yields Indoxyl. When Indoxyl is oxidized, you get Indigo Blue. Fermentation colored the world! (just not my beer)
looks like the little science kit i bought for my daughter the other day, came with red cabbage powder, citric acid and baking soda that yields the same effect.
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