Sourdough's tang comes from two acids, and they taste different. Lactic acid is soft, dairy-like, closer to yogurt. Acetic acid is sharp and vinegary. Every starter makes both; what shifts is the ratio.
Water content is one of the main levers on that ratio. A wet, slack starter favours acetic production — sharper, more assertive. A stiff, dough-like one favours lactic — mellower, sweeter, more complex in a rounded way.
The stiff one also ferments more slowly and holds its peak much longer, which turns out to matter as much as the flavour. A liquid starter gives you maybe an hour at peak before it starts sliding. A stiff levain can sit near its best for several, which makes timing dramatically more forgiving.
Temperature is the other big lever, and it interacts: cool and stiff pushes hardest toward mellow; warm and wet pushes hardest toward sharp.
| Liquid (100%) | Stiff (50–60%) | |
|---|---|---|
| Texture | Batter, pourable | Firm dough, kneadable |
| Flavour | Sharper, more acetic | Sweeter, more lactic |
| Speed | Faster to peak | Slower |
| Peak window | ~1 hour | Several hours |
| Reading it | Rise in a jar | Rise, plus it domes and cracks |
| Keeps | Days | Longer — less water, slower |
| Best for | Everyday, most recipes | Enriched dough, panettone, forgiving timing |
To stiff: feed with half the usual water. 20 g starter, 100 g flour, 50 g water gives you 50% hydration. It'll feel like firm bread dough — knead it briefly into a ball and let it rise in a jar. Two or three feeds and the culture adjusts.
To liquid: the reverse. Match water to flour by weight and it's 100%. This direction is faster; a wetter environment is easier to move into.
Expect a lag. The first feed after a conversion is usually sluggish while the population rebalances toward the organisms that prefer the new conditions. By the third it should be predictable again.
Notes from the counter
Most people should stay at 100% and stop thinking about this. It's easy to measure, easy to read, and works for essentially every recipe you'll meet.
The genuinely useful case isn't flavour — it's the peak window. If you keep missing peak because life happens between 4pm and 8pm, a stiff levain gives you hours instead of one, and that's a scheduling fix disguised as a technique.
The flavour difference is real but subtler than the internet suggests. It's noticeable side by side. It is not going to rescue a loaf that was mis-read at bulk.