Scientists work tirelessly to uncover the mysteries of the natural world, from the reasons we binge eat to the best way to wash our hands. Now they’ve figured out why coffee served in white mugs tastes so bitter. Researchers found that the contrast between the color of coffee and a white mug makes the joe look and taste bolder (read: more bitter). By the same line of thinking, coffee served in clear glass mugs tastes sweeter.

So, yes, those lab rats (the people, not the animals) are obsessed with getting (and studying) that jolt of java. This recent study got us thinking: What other crazy things do we know about coffee thanks to science? Answer: a lot.

1. The optimal temperature to serve coffee

Researchers at the University of Texas were tired of brewing coffee, taking a sip, and burning off a layer of taste buds because the brew was scalding. So they got 300 test subjects to determine what temperature makes coffee drinkable but not mouth burning. Those brave test subjects found that the sweet spot is 136 degreesCalculating the optimum temperature for serving hot beverages. Brown F, Diller KR. Burns: The Journal of the International Society of Burn Injuries. 2008 Aug;34(5):648-54..

2. The best time to drink coffee

We’ve been conditioned to get our caffeine fix first thing in the morning (just take a look at the line out the door at your local Starbucks around 8 a.m.). But as Steven Miller, a psychology professor at Rosalind Franklin University, points out, early mornings are probably the worst time to drink a cup of coffee. If we pay attention to our circadian rhythms, specifically the points when our cortisol levels (the magical way we naturally feel alert) are low, we should drink coffee in the late morning (9:30 a.m. to 11:30 a.m.) and during the afternoon slump (1 p.m. to 5:00 p.m.)Modified-release hydrocortisone to provide circadian cortisol profiles. Debono M, Ghobadi C, Rostami-Hodjegan A, et al. The Journal of Clinical Endocrinology and Metabolism. 2009 May;94(5):1548-54.Persistence of circadian rhythmicity in a mammalian hypothalamic “island” containing the suprachiasmatic nucleus. Inouye S T, Kawamura H. Proceedings of the National Academy of Sciences of the United States of America. Nov 1979; 76(11): 5962–5966..

3. The coffee-ring effect

Spill coffee on your shirt and when it dries, it looks a little like a tree stump—light on the inside, dark around the edges. Scientists at the University of Pennsylvania spent more than a decade determining what causes those outer rings. The culprit: the shape of the particles. Round particles form a defined outer ring, while elongated ones do notSuppression of the coffee-ring effect by shape-dependent capillary interactions. Yunker PJ, Still T, Lohr MA, et al. Nature. 2011 Aug 17;476(7360):308-11..

4. A coffee a day keeps the ringing at bay

If we’re being technical, it’s four cups of coffee a day. A study tracked the incidence of tinnitus (a constant ringing in the ear) among 65,000 American women over the course of 18 years. Those who had one cup of coffee a day were 15 percent more likely to have tinnitus than those who had four or moreA prospective study of caffeine intake and risk of incident tinnitus. Glicksman JT, Curhan SG, Curhan GC. The American Journal of Medicine. 2014 Aug;127(8):739-43..

5. Try a coffee nap

Coffee and naps don’t seem like a dynamic duo: One would think that the stimulative effects of coffee should stop you from being able to nap in the first place. But it turns out the boost of energy you get from a cup of coffee doesn’t happen in an instant. It takes upwards of 20 minutes for the caffeine to be absorbed by your body. Researchers at Longborough University found that drinking a cup of coffee and immediately lying down for a 15-minute nap kept tired drivers more alert than trying just coffee or a napCounteracting driver sleepiness: effects of napping, caffeine, and placebo. Horne JA, Reyner LA. Psychophysiology. 1996 May;33(3):306-9.. We usually stick to a playlist with bumping beats to keep us awake on the road.