Dufour, in his Traitez nouveaux et curieux du café (1685), already answered the three questions that Europe was asking about coffee. Does coffee sober one up? He tells of a friend who loses at piquet because he has been drinking, takes a cup and goes back to play with a clear mind. The modern answer is no, without reservation: caffeine removes drowsiness, it changes neither the alcohol in the blood, nor the speed at which the liver eliminates it, nor the impairment of judgment and coordination; it removes the alarm and leaves the danger.

Of all the beliefs of 1685, it is the only one that has lost nothing of its vigor, because it rests on a true sensation, and the only one that kills. Does it cause sterility? Dufour refuted Simon Pauli with a sound argument (the countries where the most coffee is drunk are among the most populous) and a false explanation (the sulfur would stay in the grounds). No, and the right conclusion never validated the reasoning.

Does it cure gout? He produced a Marseille monk cured at 72; modern epidemiology does associate regular consumption with a lower risk of gout. He was right the way one is right at the lottery.

Dufour, Traitez nouveaux et curieux du café, du thé et du chocolate (1685), pp. 113-114, 133; Poole et al., BMJ 2017; LC ch. 7 and 19

The fourth belief does not date from 1685 but comes back in every training course: coffee dehydrates, one would need a glass of water per cup. Caffeine is indeed diuretic, especially at high dose and in the non-habituated, and the effect fades with habituation like the one on blood pressure. But a cup is a dose of caffeine dissolved in water, and crossover trials in which the same people drink coffee at one time and water at another in identical volumes find no difference in body mass or in blood and urinary markers of hydration in habitual consumers at ordinary doses.

The extra urine remains less than the volume drunk: a coffee counts toward what one has drunk, it is not subtracted from it. This does not hold for a long effort in great heat, nor for the dry mouth after an espresso, which comes from astringency.

LC ch. 19, from the hydration crossover trials cited; MDPI 2020, pp. 209-210 for habituation