

Onions don’t shrink as much, say mushrooms. This is because of their cellulose structure that holds up fairly wellonheat…for a time.
If you cook 1 cup of onions on a high heat skillet versus a low heat skillet both for 5 minutes, the low heat volume and weight will be more. That’s because it takes high heat over time to break down the cellulose walls.
If you’re making a gravy, you have some control and variance over how this works. If you hit them with high heat first, THEN add broth to boil them down, you’ll have less volume.
I assume you’ll be using a flour Roux, you don’t want high heat at all because it will burn the flour mixture and give it a horrible taste.
So let’s assume you’re doing low and slow, and you’re thinly slicing the onions and mixing everything in, you’ll expect to retain 1/2-3/4 of the volume of the onions depending on the LENGTH OF TIME it is exposed to heat.
The longer you cook, the lesser the volume taken by the onions.
Hope that makes sense.









Beef shrinks up to 1/2, and onions also shrink up to 1/2 depending on heat.
Should be easy to figure out.