Doughnuts are best 10 minutes after leaving the fryer. They are still good for a couple hours. After about 6 hours you’ll notice the glaze (especially chocolate glaze) getting soft and starting to slide off the doughnut. This is the sticky finger phase of doughnut eating.
It’s pretty amazing how fresh doughnuts put in the break room at 7:15 AM are so different by 5pm. Microwaving a few seconds helps some. By the 2nd day very few people will eat one of those doughnuts. Even the microwave can’t resuscitate them. That sticky, watery glaze is just nasty. They are in the trash by noontime.
Why the short shelf life? Compared to other bakery items like fresh cookies or cake which easily last three or four days.
Rolls last a few days if kept in zip lock bags. Biscuits are stale and hard by day 2. They go bad in a different way than doughnuts.
Whats the Straight Dope? Why do bakery items like doughnuts change so much in 8 to 10 hours?
Water content. Donuts and Biscuits have a lot of water in them, so drying them out over time has a big effect. Cookies don’t have a high water content, so there’s nothing to dry out. Cakes have a protective layer of frosting to keep them moist.
I think bob++ is probably making reference to a fairly well-known case in the UK where a company was arguing with HM Customs & Excise over whether one of its products (Jaffa Cakes) was a biscuit/cookie or a cake, the difference being whether the product would then be zero-rated for VAT or not.
By no means always, and they still stay good a lot longer than doughnuts. (I am not even sure the OP is right that doughnuts stay at their peak for as long as 10 minutes. I’d say they are best just seconds out of the fryer.)
I was including the time they cool before glazing. We used to watch our local doughnut shop cook them. They raised the tray out of the grease and let the doughnuts cool three or four minutes before dipping them in the glaze. They were still so hot we couldn’t eat them for another couple minutes. They were so incredibly good when still hot.