Do i let Santa Rosa plums ripen on tree?

I have a nice crop of Santa Rosa plums due to the rare cold snap last winter in Southern Calif. Should i allow them to ripen on the tree or pick them and let them sweeten up in the house?They are a good size and firm with full color, but still sour. Also, what is the white powder on the skin? I think it's a normal thing. It's not mildew. It sort of looks like a protective cover to refelect the sunlight so the skin doesn't burn. Not sure. Anyone know? Thanks.
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All plums get that dusty bloom on their skin, as do grapes. I think it's a fungus that lives on the sugar that gets through the skin from within the ripening fruit. Quite harmless. I think it's called must, though my Macquarie Dict will have none of it! Nor does it mention elephants ... -- John Savage (my news address is not valid for email)
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Thanks for your reply. I'm going to read up on must. Cherers, Bob.
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I did a search. It is called plum bloom and it is a protective coating that prevents the fruit from drying out,
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