Sour Apricot Beer Turned Purple!

Might be a dumb question but.... When adding apricots, what did you use as the apricot source?

Puree, Whole Fruit, Skinned or non skinned apricot, with seed or without... etc?

Im guessing the skin of a very ripe apricot which has a purplish color in some spots or if it was added with the seed (sometimes has a purple tinge around seed and meat)?

This is a wild guess btw, im not too sure what it could possibly be but those would be my guesses.

 

Possibly anthocyanin reacting to low ph solution? That's my guess, I'm certainly not a food chemist though.

 

I'm thinking something like this, extracted from skins. (OP, were skins present?). I say skins because I used apricot in a sour and saw nothing like this. I used a canned product, so processing also could have a role? I'm also not a food chemist but one of my old chem profs had a hobby -- he and his wife explored pH indicator capabilities of flowers (don't judge - some of you probably geek out on water chem). So I started to look at some papers and it seems that anthocyanins tend to go from red to purple to blue when pH increases, not decreases. But that's as far as I got. There is no one anthocyanin, so molecular variation on this class of compounds might still account for it. Or it could be some other compound, but pH change seems likely as the driver. To me (a former sort-of chemist).

 

Never seen a color change that severe, but "purple taint" is a somewhat common issue with sours. Usually happens after transferring, so I suspect oxygen plays a role. Surprisingly there are reports of it going away with time.

 

I've seen something similar happen when a friend put a cheap "stainless" scrubby in his keg (under the diptube) and it proceeded to turn his beer a gnarly dark brown almost black color.
There is an old woodworkers trick of using vinegar and steel wool to create stains for wood. I could see a sour beer and some cheap stainless hardware doing this.

 

Your embedded picture didn't work. If it's on flickr or something, just post the link. Otherwise, you have to find out the actual image url (not the *page* url) and copy/paste that into the image url field on the 'insert image' pop-up.

 

That was a really interesting thread, thanks for sharing it. And it probably bears monitoring that thread, it appears to still be active with some experiments ongoing.

Based on what I read there, it seems like this could be oxygen reacting with a byproduct of Brett(?). It also seems that normal sour cultures can metabolize the purple color and its flavors if kept warm and roused. Even bottle conditioning appears to fix it. Neat.

 

Why do you think oxygen plays a role when nitrogen is the most common element in air?

 

Here's a fun fact. Iodine plus starch = purple.

Did @_Joe_ use Iodophor to sanitize the keg?

 

Damn, I thought for sure that Brew_Betty had nailed it. Oh well. And I don't have anything else to offer.

 

Nitrogen is pretty inert compared to oxygen (e.g., oxidation, aerobic microbes etc.).

Do you have a potential explanation that would involve nitrogen?

 

But not totally inert. I have no explanation for nitrogen. The only verified explanation I have involves iodine and starch.

 

I did say "suspect." Although when we are talking about how air influences beer/wort/brewing I'm not aware of any situations where the operative molecule is nitrogen. The only time nitrogen is important to beer is as inert gas to increase pressure in draft systems without over-carbonating the beer (because it has 1/100 the solubility of CO2).

 

Since you have oxygen, nitrogen, a carbonation stone, sour beers and a book about sour beers, you are obligated to conduct a gas infusion experiment.

 

This is true - anthocyanins are sensitive to pH. We do titrateable acidity measurements on cranberry juice all the time. Starting pH is around 2.3 and we titrate with sodium hydroxide up to 8.3. The juice starts red, goes purple approximately pH 5, starts to go green beyond that and ends up black. If you back-titrate down with acid it is reversible, which is a cool Mr. Wizard demo that I have actually used to demonstrate the diffference between buffering and stripping color with carbon black. One is reversible, the other is not. There are quite a few different anthocyanins (depending on the fruit) and other co-pigtments including a bunch of phenolic compounds involved, so it isn't simple chemistry by any means.

I can't speak specifically to the beer in question, but anthocyanin pigments are certainly sensitive to pH.

 

For all practical purposes relating to brewing? Atmospheric nitrogen *is* inert. The triple bond between the two nitrogen atoms is extremely difficult to break (requiring nearly 2x the amount of energy needed to break the double bond that exists between two oxygen atoms). If it were reactive, it wouldn't be used as a desolvation and curtain gas in mass spectrometers, as a 'blanket gas' in semiconductor manufacturing, etc.

 

I'm not convinced until someone saturates sour beer with nitrogen.