Normally, with some typical amount of water, when steaming vegetables my steamer never boils over.
However, when I steam shrimp, it seems like no matter how low I keep the heat or how little water I use the water always boils over.
Why is this?
Foaming is the result of proteins. For example, urine (sorry) foams when protein levels are high (persons with kidney failure can judge their urinary protein levels by how much foaming occurs). Vegetables have no protein; shrimp juices, plenty. Fats counteract protein foam formation, so egg whites ( very high protein) foam nicely, but not if any yolk or other oils are present. cream is a bit different, in that it has both protein AND fat, but that’s another story.
Some Oil will keep it down but won't alleviate it completely.
Another trick is to just season the shrimp as you normally do and put them in a ziptop bag or vacuum bag with as much of the air out as possible.
If using a ziptop bag, put everything in and with the top still cracked open a little on one side, submerge it almost to the top. Then seal it, that will push out a majority of the air.
Put the bag in and steam. Not only will there be no overflow, no messy pot. You'll never switch back :-) It's a poor mans Sous Vide.