Why do cakes and bulk substrates require different humidities?
Cakes have no casing to keep them from drying out!
Cakes have no casing to keep them from drying out! That is the only reason they need a higher humidity then bulk substrates during the MATURATION stage of mushroom developement.
Both need a high humidity to form PINS. But pins require a good evaporation rate to mature. This is why the humidity is lowered after buttons have formed with casings. Ideally, cakes should have there humidity lowered below 100 % also during the Maturation stage, but NOT at the expense of cake moisture content. You can't have them dry up.
The humidity reccomendations are ranges! 95 for pinning, and anything below that for fruiting. Fruits will develope alot faster at 85% humidity then at 90% humidity, but only if casing moisture content can be maintained.
It is the difference between mushroom moisture content and air moisture content that enables mushroom expansion. It is a concentration gradient, from high to low. As the surface area of the mushroom increases with maturation, this process speeds up.
If you are growing with cakes, cover them with wet vermiculite, and allow the humidity to drop a little during the maturation stage. Don't keep it at 100% at least get it down a little, your mushrooms will get larger, and they will grow faster.