Knowing when it is done
How do we know it is done?
Start the scene or choose a stage. The animation simplifies the mechanism; what follows gives the details and the available references.
The classic gesture: the hand goes into the tank and rubs a handful of beans. As long as it feels slippery, the mucilage is there; when it grates, like washed gravel, it is done. A stick pushed into the mass says the same thing: if the hole keeps its shape, the flesh has let go. These gestures are reliable in practiced hands, but they cannot be passed on in writing.
Read the stages without animation
- The hand and the stickThe classic gesture: the hand goes into the tank and rubs a handful of beans. As long as it feels slippery, the mucilage is there; when it grates, like washed gravel, it is done. A stick pushed into the mass says the same thing: if the hole keeps its shape, the flesh has let go. These gestures are reliable in practiced hands, but they cannot be passed on in writing.
- The graduated coneThe most widespread instrument is a small graduated cone filled with beans at the start and left in the tank: as the mucilage dissolves, the contents settle, and the graduation gives a figure that two people can compare. It remains sensitive to the initial filling and to bean size.
- pH, Brix, temperaturepH is reproducible and inexpensive, but indirect: it measures what the microbes have produced, and its thresholds are specific to each station. Brix tracks the sugar that remains, a good indicator of speed, a poor indicator of the stopping point. Temperature is not used to decide: it explains after the fact.
- The bean, never measuredNone of these methods measures what has passed into the bean: they all measure the state of the bath. A transfer is steered by monitoring its starting medium.
To remember: Touch, cone, pH, Brix: each method reads the state of the bath, none reads what has passed into the bean.
Read the full article and its sources ↓
This is the real skill of the trade, and it still depends a great deal on the hand.
The classic gesture: the hand goes into the tank and rubs a handful of beans. As long as it feels slippery, the mucilage is there. When it grates, like washed gravel, it is done. Another gesture is to push a stick into the mass: if the hole keeps its shape instead of closing up, the flesh has let go.
These gestures are reliable in the hands of someone who has practiced them for ten years. They cannot be passed on in writing, they cannot be checked remotely, and they tell nothing to the person who buys the coffee six months later.
Hence the instruments. The most widespread is a small graduated cone that is filled with beans at the start of the fermentation and left in the tank: as the mucilage dissolves, the contents settle, and the graduation says where things stand. It is simple, it costs little, and above all it gives a figure that two people can compare.
The end-of-fermentation methods, and what each is worth
- Touch and stickFree, immediate, and the only one that really integrates the state of the mucilage. Not transmissible and not traceable.
- Graduated settling coneThe Fermaestro and its equivalents. It measures the volumetric shrinkage of the mucilage, therefore exactly the quantity that matters. Sensitive to the initial filling and to bean size.
- pHReproducible, inexpensive, but indirect: it measures what the microbes have produced, not the state of the mucilage. The thresholds are local.
- Degrees BrixTracks the consumption of sugar. A good indicator of speed, a poor indicator of the stopping point, because the mucilage can remain sticky while the free sugar has disappeared.
- TemperatureNot used to decide, used to explain after the fact why the same duration did not give the same result.
None of these methods measures what has passed into the bean. They measure the state of the bath. This is a real limit of process control today: a transfer is steered by monitoring its starting medium.
In this plateThe 10 sections
- 01What we call fermenting
- 02What ferments, and what does not
- 03Who does the work
- 04What happens, hour by hour
- 05Who really detaches the sweet flesh
- 06“Anaerobic,” the most misused word in the trade
- 07Knowing when it is done
- 08What goes wrong
- 09What fermentation really changes in the cup
- 10What we do not know
The table of contents, with the first sentence of each section