The Metamorphic Petrology of Ice Cream
I was struck by the similarity of these two images. Which one does your dentist want you to eat?
I won’t speculate about anyone’s dentist’s motivations, but the top image comes from The Science of Ice Cream, and the bottom from the USGS. I’m not sure what conditions the ice cream was stored under, but the USGS image is from a limestone that had been stored next to a piping hot intrusion of monzonite, and partially baked into marble.
Frozen desserts left in the freezer too long will undergo a similar process. The edges of each ice crystal are constantly exchanging water with the sugar solution. Small crystals, which have a lot of surface area, will tend to shrink especially fast while the more energetically favorable crystals (in the ice cream’s case, it’s just big ice crystals that are better than small ones, but in rocks it is usually a different mineral phase) will tend to grow. This process is accelerated at higher temperatures, which is why it’s a bad idea to leave a carton of ice cream sitting out on the counter even if it doesn’t obviously melt.
Here, the top image is of fresh ice cream, and the bottom is of the same ice cream after it’s sat in the freezer for 7 weeks:
Donhowe et al., 1991. Determination of ice crystal size distribution in frozen desserts. J. Dairy Sci. 74 (10).
It’s not freezer burn and off flavors from sitting next to fish fillets that make old ice cream taste bad – or it’s not just freezer burn and fish, anyway. Our perception of taste is closely linked to texture and mouthfeel, and those giant ice crystals are just yucky.