Baristas have come a long way in recent years to abolish many myths of coffeemaking. One that remains fairly steadfast is the polish; the quick spin at the end of a tamp to make the surface of the coffee look smooth. I’ve spun a tamper in many a basket over my years and found it embarrassingly hard to stop. It’s a satisfying little flourish at the end of one’s dosing routine, and can make a strong habit.
Here’s (briefly) why it doesn’t matter, and why it’s probably bad for coffee quality.
Why it doesn’t matter
Water doesn’t care how shiny the top of the coffee grinds are. It also doesn’t care if a few errant grinds are sitting on the surface of the puck. It hits the coffee, washes it around, loosens some grinds, swells the puck and then hits hard. It’s raining down with a force of roughly 9 atmospheres behind it – a pressure that makes surface finish immaterial. What really matters is how well you distributed and tamped the grinds. Here’s a few previous posts about distribution and tamping…
Why it’s probably bad for coffee quality
Humans suck at doing things precisely and consistently. We’re not robots. Tamping horizontally with enough force is already a task that tests our mettle. Why introduce a spin? We’re more than likely to… ‘screw’ it up.
If you’re still applying any force OR lift and drop the tamper on the grinds while spinning (a very common occurrence) you’ll change the distribution of grinds and make the extraction less even. You might think you’re spinning on a perfectly horizontal plane, but you’re not. You’re human, and your arm isn’t a servo motor. What’s most likely happening is a little bit of nutation (see here for more info on nutation). That little bit of nutation means you’re compressing the grinds on one side of the basket, making it more difficult for the water to travel through. If the water meets resistance in one area, that coffee will be less extracted than the rest.
Spend less time worrying about the surface finish of your coffee grinds, and more time perfecting your distribution method. Spend less time pretending to be a robot, and more time doing something that robots can’t – like delivering excellent customer service.