Whipping carton egg whites

I’ve had it work once, and never again. Well, twice, the second time I literally whipped them for 20 minutes. I’m just curious as to why it doesn’t work as well as shell egg whites even if it’s no filler just egg whites in a carton. They always appear thinner so I imagine that has something to do with it but just curious scientifically as to why it doesn’t work or perhaps it does and I’m doing something wrong.

packaged egg whites are pasteurized - their reluctance to whip up like “regular ole’ eggs” is a well reported issue…

from:
http://www.safeeggs.com/eggs/egg-whites
Occasionally, the egg whites that have been pasteurized will not whip up as well due to the heat used in the process. To correct this try adding an extra egg white or up to 1 teaspoon of cream of tartar. As with all eggs, the fresher the egg, the easier it will whip up. Temper the eggs while still in the shell to room temperature. Another trick: Use a stainless steel mixing bowl and a whisk attachment on your home mixer.

Thanks. I buy eggs from the farm so incredibly fresh and explains the huge difference in whip time. I might try the added fresh white to see if that works, I’ve tried cream of tartar with no success

Some brands have whipping agents added, and those do whip up like normal or close to it. But I’ve only found those frozen in half gallons. The pints of whites you get in the grocery store usually say somewhere on the carton that they’re not suitable for whipping.