How to Make a Yeast Starter: A Step-by-Step Guide
A yeast starter grows more healthy yeast before brew day. Here is the starter recipe, rough sizes by batch, and how to time, pitch or decant it.
In this post
The short answer: a yeast starter is a small batch of wort, about 1.036 gravity (100 g of dry malt extract per litre of water), that you pitch yeast into a day or two before brew day so you pitch more, healthier cells. Use one for lagers, beers above about 1.060, and older liquid yeast. Boil it, chill it, pitch the yeast, keep it on a stir plate or shake it often, then pitch it at high krausen or chill it and decant the spent wort.
| Beer (5 gal / 19 L) | Rough starter size |
|---|---|
| Ale up to 1.050, fresh liquid yeast | 1 L, or none |
| Ale 1.060–1.070 | 1.5–2 L |
| Ale over 1.075 | 2–3 L, or two packs |
| Lager 1.050 | 2–3 L |
| Old yeast (3+ months) | Step up in two stages |
These are rough guides; a pitch-rate calculator that accounts for yeast age gives better numbers.
Do you need one?
- Yes: liquid yeast for lagers, beers above about 1.060, packs more than a couple of months old, and stored harvested yeast.
- No: dry yeast. It’s cheaper to pitch another sachet. See dry vs liquid yeast.
- Optional: a fresh pack of liquid yeast in a normal-strength ale. It will ferment without one, but a 1 L starter gives a faster, cleaner start.
What you need
- A borosilicate flask (it can go on the stove) or a sanitized glass jar, big enough to leave room for foam: 2 L for a 1 L starter
- Light dry malt extract (DME)
- Foil, sanitizer, and a stir plate with a stir bar if you have one
- Optional: a pinch of yeast nutrient and a drop of antifoam
| Starter size | Water | Light DME |
|---|---|---|
| 1 L | 1 L (about 1 qt) | 100 g (3.5 oz) |
| 2 L | 2 L (about 2 qt) | 200 g (7 oz) |
| 3 L | 3 L (about 3 qt) | 300 g (10.5 oz) |
| 4 L | 4 L (about 1 gal) | 400 g (14 oz) |
How to make a yeast starter
- Time it. Start 1–2 days before brew day to pitch the whole thing, or 3–4 days ahead if you want to chill and decant it.
- Warm the yeast. Take the pack out of the fridge a few hours ahead.
- Mix and boil. Stir the DME into the water and boil gently for 10–15 minutes, with the nutrient if you use it. Watch for boil-overs; the antifoam helps.
- Cool it. Cover with foil and set it in cold water until it’s 65–72°F (18–22°C). Top up with boiled water if a lot boiled off.
- Pitch the yeast. Sanitize the pack and the scissors, then pour it in.
- Stir or shake. On a stir plate, drop in the stir bar and cover loosely with foil so air can get in. Without one, shake it hard whenever you pass by. The movement keeps yeast in suspension and brings in oxygen for growth.
- Let it grow at room temperature, 65–72°F (18–22°C). Most starters finish in 24–48 hours.
- Pitch it. Either pour in the whole starter at high krausen, or chill it in the fridge for a day or two, pour off most of the spent wort, let the yeast warm up, swirl and pitch. Decanting is the better choice for starters over 1 L and for lagers, so the spent starter wort doesn’t end up in your beer.
Stepping up
For very old yeast, or when you need a lot of cells, build in stages. Start small, about 500 mL, and when it finishes, chill and decant it, then add fresh cooled starter wort for the next step. A small, tired population does better in a small first step than dropped straight into a big one.
Troubleshooting
| What you see | What it means |
|---|---|
| No krausen | Common on a stir plate. If the wort went cloudy and a creamy layer settles when you stop stirring, it worked |
| Finished in half a day | Normal for a healthy starter; chill and decant it, or pitch it |
| Foamed over | Use a bigger flask, a drop of antifoam, and a gentler boil next time |
| Stir bar keeps jumping | Slow the plate down and centre the flask |
| Smells of sulphur or green apple | Normal, especially for lager yeast; decant it off |
| Smells sour or like vinegar, or has a film | Contaminated: throw it out and review your sanitation |
Frequently asked questions
Can I use table sugar instead of malt extract?
No. Yeast grown on simple sugars can be slow to switch to maltose, the main sugar in wort. Use malt extract, or wort saved from a previous brew day and boiled again.
Should I make a starter with dry yeast?
There’s no need. A sachet costs less than a starter, and dry yeast is made with the reserves it needs for a fast start. For more cells, pitch another sachet.
Do lager starters need to be kept cold?
No. Grow them at room temperature, where the yeast multiply faster, then chill and decant so the warm-fermented starter wort stays out of the lager.
How long can I keep a starter before pitching?
Chilled and decanted, a few days in the fridge is fine. The fresher the better; after that, give it a small fresh step to wake it up.
Related guides
High gravity fermentation, harvesting and washing yeast, how to aerate wort and how yeast make beer.