I spied this test for freshness somewhere years ago. It could have been from King Arthur. Test for freshness: Place in a small bowl. Baking Powder - 1T water with 1/4 tsp baking powder, stir. Baking Soda - 1 T vinegar with 1/4 tsp baking soda, stir. If you don't see a reaction it's time to buy new.

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