Sourdough Discard: Flour & Water Maths, Recipe Swaps and Making Less
Discard is just starter: flour and water in a known ratio. Once you know the split, you can add it to recipes without upsetting them, and keep a smaller starter that wastes less.
What's in your discard
Use the same split as for any starter: flour = discard weight ÷ (1 + hydration), with hydration as a decimal.
- 100 g of 100% hydration discard = 50 g flour + 50 g water
- 100 g of 50% (stiff) discard = 66.7 g flour + 33.3 g water
- 100 g of 125% hydration discard = 44.4 g flour + 55.6 g water
Swapping discard into a recipe
To keep a batter or dough the same, take the discard's flour and water out of the recipe's flour and liquid.
Example: pancakes that call for 240 g flour and 240 g milk. Adding 200 g of 100% discard brings 100 g flour and 100 g water. Use 140 g flour (240 − 100) and roughly 140 g milk (240 − 100). Milk is mostly water (around 87%), so this swap isn't exact. Adjust the batter's thickness with a splash more milk if needed.
Unfed discard has little leavening power on its own. Recipes such as crackers, flatbreads and many pancakes rely on baking powder, baking soda or yeast for lift, or are meant to be flat. Discard mainly adds flavour.
Adding discard to bread dough
Some bakers add a little discard to a bread dough for flavour. It counts as both flour and water, so it raises true hydration slightly. Use the reverse section of the calculator: put the discard weight under "Starter added" with its hydration, and it shows the true hydration of the mix. Old, very acidic discard in large amounts can weaken the gluten, so modest amounts are safer.
How much discard does your routine make?
With a "keep some, feed the rest" routine, the discard each feed equals what you remove before feeding. Some examples, all at 100% hydration:
| Routine | Kept | Fed | Jar after feed | Discard per feed |
|---|---|---|---|---|
| Large jar, 1:1:1 | 100 g | 100 g flour + 100 g water | 300 g | 200 g |
| Small jar, 1:1:1 | 20 g | 20 g flour + 20 g water | 60 g | 40 g |
| Small jar, 1:5:5 | 10 g | 50 g flour + 50 g water | 110 g | 100 g |
"Discard per feed" assumes you keep the same amount each time and remove everything else. A smaller kept amount makes less waste. A larger feed ratio such as 1:5:5 lets the starter go longer between feeds, but makes more starter overall. Before a bake, build only the levain you need; see levain build ratios.
Storage and safety basics
- Keep discard in a covered jar in the fridge and use it within a time you're comfortable with. It gets more sour as it ages.
- A grey liquid layer ("hooch") on top is common in hungry starters. Pour it off or stir it in.
- Throw it away if you see fuzzy mould or pink or orange streaks, or if it smells unpleasant in a way that's different from sour.
Discard from a stiff starter has a different split; see the stiff starter guide.
Using discard in bread dough? The calculator's reverse section shows the true hydration once the discard's flour and water are counted.
Open the free calculatorFAQ
How much flour and water is in 100 g of sourdough discard?
For a 100% hydration starter, 50 g flour and 50 g water. For a 50% starter, about 66.7 g flour and 33.3 g water.
How do I add discard to a recipe without changing it?
Subtract the discard's flour from the recipe's flour and its water from the recipe's liquid. For example, 200 g of 100% discard replaces 100 g of flour and about 100 g of liquid.
Can sourdough discard make bread rise?
Unfed discard is usually too weak to leaven bread reliably on its own. Most discard recipes use baking powder, baking soda or yeast, or are meant to be flat.
How can I make less sourdough discard?
Keep a smaller amount of starter, for example 20 g, and feed it small amounts. Build a larger levain only when you're going to bake.