Sourdough Discard Calculator

Discard is the portion of starter you remove before each feeding. Every time you feed your starter, you add fresh flour and water in a set ratio — but first you remove a portion to prevent the jar from overflowing and to keep the acidity within the range where yeast thrives. That removed portion is called discard.

Discard is not dead starter. It still contains live wild yeast and lactic acid bacteria, just in a more acidic and less actively rising state. That makes it useful for adding flavour to quick breads, batters, and flatbreads where a chemical leavener handles the rise.

Every gram of sourdough discard is a mixture of flour and water. The exact split depends on your starter's hydration percentage. At 100% hydration, your discard is exactly half flour and half water by weight — 150g of discard contains 75g of flour equivalent and 75g of water equivalent. At 75% hydration, the same 150g holds about 86g of flour and 64g of water.

This matters when you substitute discard in a recipe. If you stir 150g of 100% hydration discard into pancakes without adjusting the recipe, you are adding 75g of extra flour and 75g of extra liquid. The calculator shows you exactly what to reduce so the batter comes out at the right consistency.

Flour equivalent: 75g — reduce your recipe flour by 75g

Water equivalent: 75g — reduce milk or water by 75g

Net result: same batter weight, same texture, added tang

Pancakes are the most popular use for sourdough discard because the recipe is forgiving and the discard adds flavour. The acids in the discard, made mostly by its bacteria, react with baking soda to give extra lift, and the tang comes through in the finished pancakes.

To swap discard into your favourite pancake recipe, use the substitution amounts from the calculator above. Reduce the flour and liquid by the corresponding amounts, then add the discard. Mix until just combined — do not overmix or you will develop too much gluten. The batter will look slightly thicker than usual before cooking; a small rest of 5 minutes allows the discard to hydrate fully.

Sourdough crackers are arguably the most impressive thing you can make with discard, requiring almost no recipe. Mix discard with olive oil, salt, and any seeds or herbs you like, spread it thinly on baking paper, score into rectangles, and bake at 350°F (180°C) for 20–25 minutes until golden and crisp. The acidity of the discard gives the crackers a complex flavour that rivals store-bought versions.

In pizza dough, discard adds tang and a slightly chewy crumb. Because discard is too weak to leaven dough on its own, always add a small amount of commercial yeast alongside it. Use the discard as a partial flour-and-water replacement (the calculator shows the exact amounts), mix and knead as normal, then let it rise for 1–2 hours before baking. For banana bread, muffins, and similar quick breads, simply stir up to 100–120g of discard into the batter — it replaces a portion of flour and milk and adds a subtle depth of flavour.

Discard keeps best in a sealed glass jar in the fridge. Every time you feed your main starter, scrape the removed portion into the jar and top it up. Label the jar with the date you started it. Over time the discard will become progressively more sour as the bacteria continue working at cold temperatures.

For the mildest flavour, use discard within one week. For crackers and savoury applications where tang is an asset, two-week-old discard works well. Beyond two weeks the smell gets very sharp and the flavour very sour, so I start fresh. Smell and age do not tell you whether discard is safe; mould or pink and orange streaks mean it goes in the bin.

Discard and unfed starter are the same thing. Discard is the name used when you remove starter as part of the feeding process. Unfed starter is just starter that has not been fed recently — whether you intentionally set it aside or forgot about it. In both cases, the starter contains active cultures in an increasingly acidic environment.

The practical difference is timing. Fresh discard (removed right before or right after feeding) is at an earlier stage of fermentation. Very old discard that has sat unfed for days or weeks is at a much later stage. Both can be used in baking, but older discard is significantly more sour. Some bakers keep a separate "discard jar" in the fridge and add to it over several weeks, using the accumulated discard in large batches of crackers or pizza dough.

If you bake frequently, a rolling discard jar is the most practical approach. Keep a 500ml or 1L jar in the fridge and add discard every time you feed your starter. Do not add fresh discard on top of very old discard without using some of the older batch first. A good rule is to use about half the jar before adding more, which keeps the average age balanced.

If you have more discard than you can use quickly, consider drying some of it. Spread a thin layer on baking paper, let it dry at room temperature for 24–36 hours until completely brittle, then break it into flakes and store in an airtight jar. Kept completely dry, it lasts for months and can be rehydrated with a little warm water to use in recipes.