Sourdough Starter

Sourdough Starter

7/10 days to establish, lives in your fridge indefinitely

What is sourdough

Bread made without commercial yeast. Instead of a packet, you grow your own culture of wild yeast and bacteria using flour and water. That culture is the starter. You feed it, keep it alive, and use it to leaven every loaf.

The bacteria produce lactic and acetic acids during fermentation. That is where the tang comes from and why sourdough keeps longer than commercial yeast bread.

A short history

The oldest form of leavened bread, going back around 6,000 years to ancient Egypt. Someone left a dough out, wild yeast got into it, and the result was lighter than anything made before.

For most of human history this was the only way to make bread rise. Bakers passed starters between generations. Commercial dried yeast only became widely available in the late 19th century and within a few decades had replaced sourdough almost entirely.

It never fully disappeared. It came back into the mainstream during the 2020 lockdowns when people started baking at home and realised growing a starter was something you could do with a jar and some flour.

What is in a starter

Two things living together: wild yeast and lactic acid bacteria. The bacteria create an acidic environment that protects the yeast, and the yeast produces CO2 that makes the dough rise.

Wild yeast comes from the flour and the air. When you mix flour and water and leave it out, you are creating conditions for these microorganisms to thrive. Daily feeding selects for the ones you want and builds a stable culture over time.

In a mature starter, bacteria outnumber yeast cells by roughly 100 to one. The yeast does the lifting, the bacteria do the flavouring.

How it replaces commercial yeast

Commercial yeast is a single strain bred to work fast. It rises in 1/2 hours and adds almost no flavour.

A starter contains multiple wild yeast strains alongside bacteria. It works in 4/12 hours depending on temperature and strength. The slower fermentation builds flavour, improves digestibility and gives the bread better shelf life.

No packet needed.

Reviving a neglected starter

Weeks in the fridge without feeding is fine. It is almost certainly still alive.

Check first. Pour off any grey or brown liquid on top. This is hooch, just alcohol from a hungry starter. If you see pink, orange or fuzzy mould in the jar, bin it and start fresh. Anything else is fine.

Left at room temperature rather than the fridge? The revival process is the same but expect 5/7 days rather than 3/5, and it may not come back at all. Room temperature accelerates fermentation until all the food runs out, which is harder on the culture than a slow fridge starvation. If it shows no signs of rise after 7 days of twice-daily feeds, start fresh using the section below.

1. Scrape off any dried crust from the surface. Take 10g of starter from underneath and transfer to a clean jar.

2. Feed with 25g strong white flour and 25g filtered water. Stir well, loosely cover, leave at room temperature.

3. Repeat every 12 hours for 3/5 days. Each feed: discard down to 10g, add 25g flour and 25g water.

4. Ready when it doubles within 4/8 hours of a feed and smells fruity or lightly tangy.

Use filtered or bottled water. Chlorine in UK tap water can slow fermentation. Leaving tap water out overnight also works.
A spot near a radiator or on top of the fridge speeds things up in winter.

You can feed into the same jar without cleaning it. If you do switch jars, rinse with hot water only. No soap. Residue kills the culture.
The discard step matters. Adding flour and water on top of a large starving starter won’t work. There isn’t enough fresh food relative to the exhausted culture. Taking 10g and feeding that proportionally means the fresh food is enough to do its job.

Making a starter from scratch

Per feed

rye or wholemeal flour   50g
filtered water           50g

Start with rye or wholemeal. More wild yeast than white flour. Switch to strong white once established if you want a milder flavour.
Use a tall jar and mark the level with a rubber band after each feed so you can see the rise.

Day 1. Mix 50g flour with 50g filtered water in a clean jar. Stir well, loosely cover, leave 24 hours at room temperature.

Days 2/4. Discard all but 50g. Feed with 50g flour and 50g water. Loosely cover, leave 24 hours.

Days 5/7. Switch to every 12 hours. Same amounts each feed.

Day 7/10. Ready when it doubles within 4/8 hours, has bubbles throughout, and smells fruity and slightly tangy.

Nothing happening in the first 2/3 days is normal. By day 4/5 you should see clear bubbling.
Cold kitchens slow things down. Ideal temperature is 24/26°C.

Storage and maintenance

Keep in the fridge in a loosely covered jar. Feed once a week minimum. The night before baking, take it out, feed it, leave at room temperature overnight and it will be ready in the morning.

Baking weekly, leave it on the counter and feed daily. Baking occasionally, fridge and a weekly feed is enough.

A well-maintained starter lasts indefinitely. Some bakeries use starters decades old.

What to do with discard

Use it. Discard is unfed starter. Works well in pancakes, flatbreads, crackers and pizza dough. No fermentation needed, mix it in and cook same day.

Garden. Keep a small airtight container in the kitchen for discard, raw dough scraps and flour residue from bowls. Every few days take it down the garden.

Herb patch: dilute 100g discard with 1 litre of water, water directly onto the soil once a week during growing season. Good for basil, parsley, chives and mint. Don’t overdo it as the acidity can lower soil pH over time.

Compost: tip the container into an outdoor compost bin. The yeast and bacteria speed up decomposition and boost the microbial activity in the pile. Add gradually rather than large amounts at once.

Raw dough scraps and flour residue go in the same container. Avoid anything cooked or baked as it attracts pests.
UK councils often subsidise or give away compost bins. Worth checking before buying one.