How it works
Sours are balanced on sugar and acid. Lime and lemon juice are roughly 6% acid; most other juices are far less. Adding measured powdered acids lets you bring orange, grapefruit, pineapple or even leftover fruit juices up to citrus-strength.
Orange juice to lime strength
Per 1 liter of orange juice: 32 g citric acid + 20 g malic acid.
Why it matters
Consistency (juice acidity varies by season), less waste, and new flavor options for sours. Popularized by Dave Arnold.