anybody else notice that as this stuff ferments, it changes color?
is there a name for this?

--
billb
Since time immemorial, the powerful have used religion to distract
the oppressed, to encourage them to focus on the next world so that
they will acquiesce to the injustices of this world. If you would
have your slaves remain docile, teach them hymns.

It has to do with the anthocyanins in the skin. Anthocyanins are
phenolic copmpoounds like tannins. Their color is dependent on the pH
they are at (as well as other things). At an acidic pH they appear
red, turn colorless from around 4-6 and then turn green at basic pH.

So if your wine is turning color during fermentation, you are either
raising the pH too high (>4, which is bad) or the pH is decreasing
(which is not so bad).

There are a lot of different anthocyanins though, and the exact pH at
which they change is different for each. I notice that my rhubarb wine
changes color from green to red during fermentation. I am assuming
that is becasue the yeast is actually lowering the pH.

I'd say it's going from purple to red.

--
billb
Since time immemorial, the powerful have used religion to distract
the oppressed, to encourage them to focus on the next world so that
they will acquiesce to the injustices of this world. If you would
have your slaves remain docile, teach them hymns.
"Droopy" > wrote in message
ups.com...
> It has to do with the anthocyanins in the skin. Anthocyanins are
> phenolic copmpoounds like tannins. Their color is dependent on
the pH
> they are at (as well as other things). At an acidic pH they appear
> red, turn colorless from around 4-6 and then turn green at basic
pH.
>
> So if your wine is turning color during fermentation, you are
either
> raising the pH too high (>4, which is bad) or the pH is decreasing
> (which is not so bad).
>
> There are a lot of different anthocyanins though, and the exact pH
at
> which they change is different for each. I notice that my rhubarb
wine
> changes color from green to red during fermentation. I am assuming
> that is becasue the yeast is actually lowering the pH.
>

Still hard to say. The anthocyanins could be moving to colorless
giving a lighter color, or the green color could be movie toward
colorless making it appear more red. The only way to know for sure it
to take a starting pH and an ending pH.

There are other possibilities, these color compounds can oxidize/reduce
also. In freshly fermnted wine, full of sulfite there is very low O2,
the wine will appear redder and more vibrant. As the wine ages, some of
these color compounds oxidize and turn less ruddy, more rusty in color.

If you want to go out and make 100 grand a year, become a food color
scientist or a food flavor scientist. It is all about how to keep your
wine red and your bread fresh so it can sit on the shelf for weeks,
months or years.

I'm not sure this is what you are looking for but the end of
fermentation is always visible by a color change. It goes from murky
to the color of the wine and stratifies. Clearer wine is a deeper
version of the the femrenting wine color.
Joe