Ask for a sign of ripeness and red comes to mind first. But standing in the farm, there are many moments when colour alone cannot decide. Varieties redden differently, colour sinks in the shade, and after rain the wet fruit looks different. So besides colour we look at feel and time. Here is how that lines up with the research.
Hook a finger and pull lightly. If it comes away cleanly it is ripe; if it holds on, it is still early. We also feel the softness of the pulp. Conversely, fruit that gives with no spring when pressed is over-ripe. The harder a lot is to read by colour, the more we put this hand sense first. For varieties whose ripe colour is yellow, especially, we rely on feel.
The hand sense has several lines of support. First, detachment force. Unripe fruit needed about 7.71 N and ripe fruit about 4.27 N, so ripe fruit came off with roughly half the force (Ferreira Júnior et al., 2018). A detachment study on a different variety points the same way (Zhou et al., 2025). Next, the reversal of hardness. As ripening proceeds the pulp softens from 17 to 7 to 2 MPa, while the bean hardens from 7 to 42 MPa. Go on to over-ripeness and the fruit loses about 70% of its elasticity (contact stiffness) compared with the ripe state (Tinoco et al., 2022). Another study found fruit firmness falling about 44% from unripe to ripe, with pH falling from 4.64 to 4.02 (Dharmaraj et al., 2025).
Then time. Arabica reaches ripeness an average of 220 to 243 days after flowering, and the inside of the bean (the filling of the endosperm) finishes about a month before the colour (Unigarro et al., 2025). Sugar rises sharply late in ripening, around the point where the colour turns fully red, and the acids change in character rather than simply increasing (Dong et al., 2024; Li et al., 2023). Colour is the last sign to appear; the filling of the inside runs ahead of it. So if you count days from flowering you can predict the time to pick before waiting for colour.
Colour is the last sign. I go to read ripeness before it, by hand and by the calendar.
Do not make colour the only criterion for sorting. Add to colour: does it come away with a light pull, is the pulp soft, and how many days since flowering. Aim to pick not at the first blush but at the full red with sugar on it. Treat the softness of over-ripeness as the upper-limit sign and leave it out. Easy to say in words; in fact it is the hardest thing in producing coffee.
From this season we have begun recording flowering date and harvest date for each plot. Only with colour, hand and calendar together can next year's picking time be read in advance.
For why ripeness splits on the same tree, see Why fruit of different timing shares one tree; for reducing unripe fruit, How to reduce unripe cherries; for the whole picture, the overview of harvest.
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