Crusty Cupping Experiment
by BH Learn
SCA cupping guidelines
state that breaking the crust should take place after 3-5 minutes. In practice, many coffee professionals aim to break the crust exactly 4 minutes after pouring each cup, but in larger cuppings it’s not always possible to be this accurate.
Cupping is supposed to ensure all coffees get the same treatment, so that any difference between cups are due to differences in the beans or roast, not the brewing method. We looked into how important the timing of the break is, and noticed that breaking the crust later, after 5 minutes rather than 3, seemed to lead to higher extractions.
We suspected that the crust might be insulating the surface of the coffee, keeping the temperature up during the steeping time, and thus allowing for slightly higher extractions. We set up an experiment to test this idea out, and to establish exactly how important the timing of the break is.
What we found isn’t what we expected: insulating the surface of the cups seems to have little effect. However, we did come up with a purely mathematical approach that might explain why breaking the cup later can lead to higher extractions.
We set up two parallel cuppings of the same coffee, all from the same roast batch. In the first set, the crust was broken in each cup, by stirring to the bottom 4 times, at different times: immediately after pouring, or 1, 3, or 5 minutes after pouring. In the second set, to see if insulation alone explains the effect of breaking the crust later, we broke the crust immediately and then covered the bowl with a sheet of expanded polystyrene for 1, 3, or 5 minutes.