I made a sponge cake today, filled with raspberries and cream. After 2-3 hours, it started to get greeny grey patches on it, looking a bit like mold (but not furry, just discoloured). The colour appeared mostly in places where the sponge was in contact with the raspberry cream. I can’t believe it went moldy in such a short space of time. So what happened to my sponge cake?
These are the ingredients:
eggs
caster sugar
sodium bicarbonate
cream of tartar
custard powder
cornflour
thickened cream
frozen raspberries
icing sugar
vanilla extract
Sponge cakes can mold, really fast, although that seems ridiculously fast. My wife, who makes the best sponge cakes in the whirled (but would never use raspberry) can’t think of anything other than mold that the spots might be.
My guess is that it’s a chemical reaction between the raspberries and the baking soda (sodium bicarbonate). It’s pretty common in carrot cakes. I’ve never heard of it happening with raspberries, but given what you describe, I’m not sure what else it could be.
Oh, I like this theory. There are certain vegetables and plants (red cabbage, beets, violets, etc.) that act as natural pH indicators and turn from their normally red/purple color to something greenish in the presence of a basic solution. I wonder if raspberries do the same thing? I would take some of the frozen raspberries, mash’em up with a little water, and then add a teaspoon of baking soda to the solution and see if that’s what’s going on.