1. Baking Powder
That box of baking powder you opened 18 months ago is probably still fine to use, but it won’t give your cakes and bakes that ‘oomph’ when it’s time to rise in the oven.
Once opened, baking powder begins to absorb moisture from the atmosphere which interferes with effectiveness in baking.
Keep it sealed tightly and if in doubt, check the freshness of your baking powder with this little test. Fill a mug half way with just-boiled water from the kettle, add in a teaspoon of baking powder and wait to see if it bubbles up. If it’s more of a flop than a fizz, it’s time to toss it in the bin. Always keep your baking powder in a cool, dry place.