Ingredient

Bicarbonate of soda

Pure alkali. It needs an acid in the recipe — buttermilk, yoghurt, treacle, cocoa — to produce any lift at all, and without one it leaves a soapy, metallic taste. That dependence is the whole difference from baking powder.

Sourcing
The baking aisle sells small expensive tubs; the cleaning aisle and pharmacies sell the identical thing in large cheap bags.
Quality cues
Should fizz hard when a spoonful meets vinegar. It is very stable, so it rarely fails.
Substitutions
Baking powder (use about three times as much)
Storage
Airtight and dry — it absorbs both moisture and odours, which is why an open box works as a fridge deodoriser.
Shelf life
2-3 years sealed
Nutrition

Per 100 g

Calories
0 kcal
Protein
0 g
Fat
0 g
Carbs
0 g
Fibre
0 g
Sugars
0 g
Sodium
27360 mg

From USDA FoodData Central (#175040). Raw, edible portion.

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