Why is restaurant ice clear, when my ice at home is cloudy?

Who's asking: Martha Demeritt, Sidney, ME

I had never noticed this, but Martha is right: the ice cubes you get at restaurants are clear, while the ones that come out of my ice trays are opaque. I had wondered whether this was a difference between tray ice and ice-maker ice, but Martha's refrigerator has a built-in icemaker, and her ice is cloudy, too.

The difference has two main causes. First, water in commercial (i.e., restaurant) ice-makers is filtered and sometimes even distilled to remove minerals and impurities, which make water cloudy.

Second, as Martha noted when she asked this question, restaurant ice cubes are small. This is because they're made not by freezing still water, the way tray ice and refrigerator ice-makers do, but by running chilled water over a grid. The water freezes in layers, and the cubes drop through once they reach a certain size. Freezing in layers prevents air bubbles that make the cubes opaque. Large commercial ice plants force a low-pressure air current through the freezing water, pushing air, minerals and impurities out.

Once upon a time, merchants made fortunes harvesting ice from the Kennebec River. "Kennebec Diamonds" went all over the world, with more than a million tons a year shipped out. I'm not sure I'd eat ice from the Kennebec River, although it's quite possible -- even likely -- that the river is cleaner now than it was 100 years ago.

Longtime friends of The Mystery Bookstore will want to tune in to "Dirt" at 10:00 p.m. tonight on FX, because the one and only Richard Brewer has two guest spots in tonight's episode. I've never watched the show, so producers take note: the way to get me to watch your series is to put friends of mine in the cast.