A container of bi-carbonate of soda is one of those ingredients that can sit in your pantry for months... even years! If you think it's been sitting there for a while, it's a good idea to test if it's still active. Place a spoonful of the bi-carbonate of soda into a bowl. Add a splash of vinegar or lemon juice. If it fizzes a lot, it's fine to use. If there's only a little fizz, it's no longer active.