I guess I have never noticed any difference as all leafy greens I grow go right into the fridge after harvesting and washing. We eat them only after refrigeration, not before, as warm lettuce, kale, spinach has little appeal.

Dave

Hmmm...I should probably conduct an experiment!

It definitely works for me for lettuce,and for spinach, too. Never tried it with kale. But a trick someone on GW shared with me last year, for bitter chard, was to boil it for 1 minute and dump the water. I wonder if that would work for bitter kale?

But hey -- my kale never goes bitter (cool summers here) and you're in a cool climate, too. Maybe no need?

That's funny - my chard never goes bitter no matter how hot it is, but kale is pretty much inedible between June and September. I grow different types - lacinato, Red Russian and others, and I can't stand their taste until a few frosts have occurred.

That IS really interesting.
Must be a soil issue. Or maybe a nationality issue?

Chard sweetens up in the fall when it gets colder. I am reading Eating on the Wild Side which is about plant history and which veggies have most phytonutrients. There is some information about how temperature and time effect plants because of chemical changes. Asparagus starts to lose its sweetness about 4 hours after picking. I don't recall what the book might have said about lettuce. I tend to have bitter lettuce. Trying to grow varieties at the right time. Some are better in cooler weather others do better in hot. Right now, my spinach tastes sweet to me but it's been growing in a high tunnel and starting to bolt (I'm in NH) so need to eat the rest of it soon.