Foaming oil!

Morning Glory

Obsessive cook
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Does anyone know what is happening here? This is a sliced shallot which I was cooking in vegetable oil until it went golden. This is something I've done hundreds of times. But on this occasion the oil almost immediately frothed up. I know this happens with butter but it shouldn't happen with oil.

I tasted in case something odd had got into the pan but it was just standard sweet onion taste. Could it be the natural sugars in the shallot?

83593
 
Oil depth and the amount of moisture in context to the total amount of a product, onions in this case can create what your experiencing theoretically, but I've never seen it. A compound in the shallot that reacted maybe? Heat not high enough, it's a head scratcher. lol

Did it subside as the onions continued to cook.
 
Oil depth and the amount of moisture in context to the total amount of a product, onions in this case can create what your experiencing theoretically, but I've never seen it. A compound in the shallot that reacted maybe? Heat not high enough, it's a head scratcher. lol

Did it subside as the onions continued to cook.

It was a generous tablespoon of oil and one banana shallot. It didn't subside even when I added grated ginger and garlic (I'm making a curry sauce). When I added water a bit later then it did subside.
 
...as you say the main cause seems to be water entering the oil. Possibly my plastic chopping board was a bit wet before I sliced the shallot. Or, maybe the (slightly old) shallot had a high moisture content. I do have one shallot left from the same batch and could test this again tomorrow.
 
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