In October or November, if you are working on Mason Bees; and February if Leafcutter bees, take your nest block apart with a potato peeler and scoop the cocoons and dirt out of the grooves of nesting block.
Brush out the nesting block and spray with Mason bee attractant. Attractants act as prep for next season and as an antiseptic to kill mold and mildew.
Wash the cocoons, with a spray of water, while they are in a strainer until the water runs clear. Set cocoons on a paper towel and let them dry. When dry, put them back in the Humidifier bee-safe till next spring.
Mason bee cocoons overwintered in a 34-38F (1-3C) controlled environment (your refrigerator) consume their stored fats much slower than in fluctuating outdoor temperatures and emerge stronger and ready to go to work, in the spring. Plus, you can hold them longer in your refrigerator, so you can control your release dates.
The only problem is that your refrigerator has a very low humidity around 10-20% and your cocoons will dehydrate, dry up and your bees will die.