mnick12
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Yeast corroding aluminium?
Hi everyone I just had a peculiar incident and wanted to get other peoples opinions on what has occured.
I was in process of making some ciabatta bread, which requires an 18hr rising period in bowl covered with foil. Anyway I left the dough overnight, and
in the moring there about 15-20 grey-ish black spots on the aluminium. At first I just assumed someone spilt a little jam or food product on the foil.
However upon closer examination these spots are actually very small holes, and the discoloration is corrosion of the aluminium. Keep in mind the only
part of the foil that corroded was in direct contact with the rising dough. So my question is what could bakers yeast be producing that has the
ability to corrode aluminium metal in a 12hr period?
This question may sound a little odd, but I was absolutly stunned when I witnessed it firsthand.
Thanks!
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Endimion17
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Yeah. They're living creatures and they have a semipermeable membrane for active/passive ion exchange. Thus, they change the pH of their environment
because they have a metabolism.
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chemrox
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Yeah you're probably killing a few million of them with exchange between sodium and aluminum ions. The Na is making the black spots IMHO.
"When you let the dumbasses vote you end up with populism followed by autocracy and getting back is a bitch." Plato (sort of)
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Endimion17
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There's no way sodium is produced here. How on earth could a metabolism produce it?
It's the hydronium cations being expelled out. Similar effect happens with plant roots, especially young root tips that release them, lowering the pH
and thus dissolving calcium carbonate in the ground. That's why growing plants in aluminium trays eventually corrodes them enough to make holes and
cause the soil to seep out.
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malcolmf
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I've seen that with a batch of lasagne that I made. Aluminium foil all corroded and holed where it touched the top surface. No yeast. The simplest
explanation was just electrolysis. The lasagne was in a stainless steel tray, so the foil got corroded by the current between dissimilar metals in
contact with an electrolyte (food). I switched to using clingfilm in future.
So I wonder, was the bread dough rising in a metal bowl?
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Endimion17
International Hazard
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Mood: speeding through time at the rate of 1 second per second
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No, it isn't electrolysis because there's no forced electric current. If you have two metals and an electrolyte, you've got a Galvanic cell and
therefore corrosion of the anode. Lasagna is a nonliving thing, therefore no metabolism is found in such reactions.
If you have only one metal, it's a simple chemical reaction of dissolving, most often in acids when it comes to food. Aluminium is prone to such
events.
However, we've got a live organism here, yeast, that lowers the pH of its environment upon growing. As I've said, similar thing happens with root tips
of plants (apical meristem).
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