Choose a yeast whose alcohol tolerance exceeds the strength you are aiming for: turbo yeast 18-20%, wine yeast 14-18%, bread yeast 10-14% and wild yeast usually only 5-8%. Once packets run out, keep a culture alive by growing a small starter in sweet wort and saving a measured scoop from each finished ferment, so each batch is seeded from the last.
Part of Ethanol Fuel Production
Yeast selection and propagation is choosing a strain by alcohol tolerance and keeping it alive from batch to batch without buying more.
Tolerance Decides The Ceiling, Not The Sugar
Yeast stops when the alcohol it makes poisons it. The parent’s figures:
| Yeast | Tolerates | Fermentation time |
|---|---|---|
| Turbo yeast (salvaged) | up to 18-20% | 3-5 days |
| Wine yeast | 14-18% | not stated in the parent |
| Bread yeast | 10-14% | 5-7 days |
| Wild yeast (on fruit skins) | usually 5-8% | slow, unpredictable |
Fuel work rarely needs more than the 9-12% that a 15-20% sugar wash can reach (Fermentation), so ordinary bread or wine yeast is enough; a yeast whose tolerance is below the wash’s potential strength is one cause of a wash stopping early (nutrient shortage is another; see the troubleshooting page). Yeast Biology covers what the organism needs.
What You Need
- A starting culture: a packet, a bubbling sample from a working ferment, or the skin bloom on clean ripe fruit
- Sweet wort: a lightly sweet liquid (diluted juice or malt water), boiled and cooled
- A clean jar or bottle with a loose cover
- Warmth: 25-30°C
Method: Grow And Keep A Starter
Step 1: Wake the culture. Add a pinch of yeast, or a spoon of live wash, to a litre or less of sweet wort at 25-30°C. Within 6-24 hours it should foam and smell of bread or fruit.
Step 2: Scale up. Use the foaming starter to seed a larger batch of wash. The parent’s rule for dry yeast is 5-10 g per 20 litres of wash. For a liquid starter, pour in the whole active starter and judge the result by how fast the airlock starts bubbling (6-24 hours is normal); if it is slower, make a bigger starter next time.
Step 3: Save the next seed. At the end of a healthy ferment, before racking, take a clean jar of the thick yeast sediment and keep it cool and covered with a little wash. Use it within days to weeks.
Step 4: Refresh. Every few batches restart from a small starter in clean wort to leave behind bacteria and tired cells.
Common Mistakes
- Reusing sediment from a sour batch. A vinegar smell means bacteria came with it; discard the seed.
- Adding yeast to hot wash. Above 40°C the culture dies.
- Letting the starter sit open. It turns to vinegar; the airlock logic applies to starters too.
What’s Next
- Learn next: Fermentation Vessel Design, the container the yeast will work in
- Combine with: Monitoring & Troubleshooting, for a ferment that stalls