It’s light and fluffy when we put it in a container and nearly always doubles in size by the time I get it home. +1 on euge’s suggestion on using a nalgene or some type of plastic bottle.
weird, it always seems to settle and 'halve' in size approximately for me. but I put it in a cooler with ice, so maybe you're is getting warm and causing the expansion.
+1 on plastic if you can - but if you must use mason jars, I would try to not screw the ring part of the lid all the way down, leave it a quarter turn backed off.