Turning the fermentation
Introducing oxygen at the right moment. The main lever a fermentary operator has, and where most of the skill sits.
The microbial succession in a cacao fermentation needs different conditions at different stages. Yeasts work anaerobically on the pulp sugars; acetic acid bacteria need oxygen to oxidise the resulting ethanol. Turning the mass is what supplies that oxygen.
Timing is everything. Turn too early and the yeast phase is cut short before enough ethanol has been produced. Turn too late and the interior stays anaerobic and under-acidified, so the heat and acid never penetrate the bean properly. Turning schedules — every 24 or 48 hours, and how many times — are the protocol a fermentary is really following.
What it does
Introduces oxygen to the mass, enabling the acetic acid bacteria phase, and evens out temperature and moisture between the outside and the core.
Why it matters
It is the principal control on how the fermentation proceeds, and getting it wrong produces under-fermentation even when the duration was right.
- Typical duration
- 1–2 days
- Why the range is wide
- The interval rather than the total time is the parameter. Every 24 or 48 hours are both common, and the choice depends on mass size and ambient temperature.
What it does to the flavour
Determines how completely the polyphenols are reduced and how much acetic acid is produced, which sets both astringency and acidity in the finished bean.
When it goes wrong
Turning too early, cutting the yeast phase short; or not turning enough, leaving an under-aerated core that ferments incompletely.
Related
Techniques that depend on this
- Setting up a chocolate tastingTurning admits the oxygen the acetic phase needs. Under-turned lots read in the glass as flat and astringent, which is worth being able to name at a tasting.
Sources
- ChocolateHQ editorial synthesis — ChocolateHQ(citation identity confirmed; passage not re-read)
- Chocolate Science and Technology — Wiley-Blackwell(citation identity confirmed; passage not re-read)