Baking soda holds carbon dioxide if it's still active. You can release the carbon dioxide by heating or mixing it with an acid like vinegar or lemon juice. If the baking soda fizzles upon contact with an acid, then it's still fresh.
BTW, the fact that baking soda releases carbon dioxide when heated is why it is effective for extinguishing small electrical and grease files (but NOT when there is a lot of oil, i.e. a deep fryer). The carbon dioxide released displaces the oxygen necessary for burning, thereby extinguishing the fire.
By
01/03/2011
Add a bit of white vinegar to a bit of baking soda.If it fizzes it's still good. Log onto:stilltasty.com Great site for foods shelf life.
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If you can't remember when you bought your last box of baking soda to bake with. Pour a 1/2 teaspoon vinegar onto a dab of baking soda, if it bubbles, it's fresh.
By Terri
RE: Testing Freshness of Baking Soda
Baking soda doesn't go bad. Its baking POWDER that can go bad. Test that by mixing with some water, if it fizzes, it's OK (06/19/2005)
Want to know if the baking soda in your pantry or refrigerator is still good?
Pour some vinegar in a cup or small bowl and add a bit of the baking soda. If it fizzes, it's still a-okay :-)