"We’ve all been told that coffee -- specifically, the caffeine in coffee -- is a mild diuretic, which means that it makes the body excrete more liquid than normal (read: pee more). The diuretic effects of caffeine can vary based on many factors, including your sex, activity levels and whether or not you’re used to its effects. But caffeine can also have a laxative effect in some particularly sensitive people. The chemical stimulates muscle contractions in the large intestines, which are similar to the contractions that happen after you eat a meal." We know that caffeine is the culprit because...

"The very coarse grind should yield an under-extracted brew. The grounds are so coarse that the water won’t be able to extract enough good-tasting coffee stuff from them, resulting in a brew that’s sour and grassy, with a sensation reminiscent of underripe fruit. (If you’re using a French press and want to get the full, exaggerated effect of under-extracted coffee, try brewing the very coarse-ground coffee for half the usual time. The coffee will be totally gross.)" The very fine grind should deliver an over-extracted cup. Because the grounds are so fine, the water will have no trouble extracting way...