The Fresh Loaf

News & Information for Amateur Bakers and Artisan Bread Enthusiasts

Purple hooch

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zorglub's picture
zorglub

Purple hooch

Can someone with a deeper knowledge of microbiology explain which organisms cause this?   Returning to my refrigerated starter after five or six weeks, I find the top surface has turned a grayish purple.  It smells fruity rather than sour.  I wouldn't describe the odor as acetone-like (but maybe other components are masking the acetone odor).  This isn't the first time I've observed this. 

jcking's picture
jcking

It's polyphenol oxidase, same enzyme that makes apples/potatoes/bananas brown and darken on cutting and exposure to air..

In any flour/water system deficient in oxygen, it happens. The PPO is mainly located in the bran, so tiny specks of bran in your batter become visible as the enzyme catalyzes the reaction.

Anyone who has seen the greyish surface of an overnight autolyse, particularly with wholewheat has seen the same phenomenon.

Jim

Mini Oven's picture
Mini Oven

would you call the color clear dark grey?  

Doesn't sound unusual to me if the starter is under the liquid.  If the starter itself is spotted purple or there are colonies growing on surfaces that might be another thing.  

Pour off top liquid slowly and carefully, while the jar is tipped, remove a sample from under the grey goop to feed.  It's a two spoon maneuver, one spoon to scrape away the darker gooey surface and a second clean spoon to dig deep for a chunk of creamy bottom starter.  Add water and flour and wait for the freshly fed starter to show lots of activity before discarding the old dark starter.  It may have to go thru several feeding sessions on it's way back to being usable.

Next abuse, give it more flour and thicken it up, dryish dough balls will survive longer before turning dark.  The stiffer the better.  I got samples months and even years old.

zorglub's picture
zorglub

Polyphenol oxidase is new to me.  It was indeed whole wheat flour.  The starter was originally stiff enough to stand in a rough cylinder (diameter about half the height), but when taken out of storage had slumped completely, and had a viscosity closer to porridge.  There was only a little liquid on the surface: not enough to pour off.  The color of the liquid might have been clear dark gray (too little to judge), but the starter proper had a very definite purple tint (so I imagine the liquid would be purple as well).  There was no visible fur or spotting (other than bran specs).  The starter was in a glass cup covered by saran wrap, with a rubber band around it.

I scraped away the dark surface, and several layers under it with different spoons, as Mini Oven suggested.  Wish I'd taken a photo first. The new culture already seems normal, after a single feeding and overnight culture at 67F: it has CO2 bubbles, and smells sour.

jcking,  I'm a bit confused that your first paragraph suggests PPO requires oxygen, and the second paragraph suggests PPO is inhibited by oxygen.  The discoloration was only the top: is that consistent with PPO?

I'm amazed by Mini Oven's starters that have fended for themselves for months and years.  I will make the starter a whole lot dryer the next time I need to leave it alone for prolonged periods.

jcking's picture
jcking

For a more detailed explanation do a search for polyphenol at Wikipedia.

Jim

Mini Oven's picture
Mini Oven

it is predominantly LABs, I would still feed it a few times to bring the yeast levels up.

adri's picture
adri

Did you use whole rye/wheat to feed your starter?

I know from people that it happened to them, when they fed whole wheat.

This bye the way backs the polyphenol thesis, as whole wheat has more of it as white wheat.

Adrian