Discard

Discard is the amount of starter you remove and set aside before adding fresh flour and water at a feeding. Because a starter grows in volume every time it is fed, removing a portion first keeps the jar from overflowing and keeps the ratio of fresh food to existing culture consistent from feeding to feeding.

Without discarding, a starter kept in a fixed-size jar would need to be fed with less and less fresh flour relative to its size over time, which weakens how vigorously it rises and can make it less predictable. Many bakers save discard rather than throwing it away, using it in pancakes, crackers, or other recipes that do not rely on strong leavening power, since discard still carries flavor even though it is not necessarily very active.

A second jar or container is handy for collecting discard if you plan to bake with it later, so it does not need to be scraped out of the main jar under time pressure. A common mistake is skipping discard entirely to avoid waste, which over several feedings makes a starter sluggish and harder to read. Keeping discard refrigerated if it will be used within a week or two also helps preserve its flavor.