Your Ensenada friends have perhaps seen a few too many tequila sunrises.
Matthew Alice: Is it possible that ice purchased in Baja melts faster than ice purchased in the United States? We were camping in Ensenada recently, and some friends said ice purchased there did not last as long in their ice chest as ice purchased at home. — John Wahlsten, San Diego
Could it be that Ensenada’s closer to the equator, so the ice melts faster? Or—anything you buy in Mexico is bound to be a rip-off, so the ice melts faster? Or maybe it’s NAFTA—cheap Mexican ice (which melts faster), made by oppressed workers paid only in Sno-Cones and bags of cubes. Cut-rate Mexican ice will soon overwhelm the American market and wipe out the jobs of millions of middle-class, tax-paying U.S. ice-makers.
Your Ensenada friends have perhaps seen a few too many tequila sunrises. But even if we are mighty neighborly and accept their story, country of origin probably had nothing to do with it. More likely the melt rate was affected by the temperature of the cooler when the ice was put in, the size/type of cubes, the temperature/nature of whatever they were chilling, how many times the cooler was opened...dozens of small differences. North-of-the-border ice vendors say the Mexican commercial product is virtually identical to what you get here, made with the same machinery.
On the meltability scale, block ice is most resistant, cubes are in the middle, and crushed ice melts fastest. Serious students of transcendental brewskiology (the science of carrying beer to San Felipe) know this means crushed ice cools your 12-pack fastest; speedier yet is a combination of crushed ice and rock salt.
Commercial cube-making machines are based on a simple principle. Pure H20 molecules freeze faster than any dissolved impurities do, so if you keep water flowing over (and then off) the freezing unit, you’ll gradually build up layers of pure frozen water. Some machines create an ice slab, then drop the slab onto a hot wire grid that cuts it into cubes. Some spray water up into a freezing unit indented somewhat like an upside-down mini-muffin pan. The water molecules freeze and stick, impurities drain off.
This also explains why commercial cubes are clear, while the things you crack out of that plastic tray in your Kenmore have a cloudy patch in the middle. Water molecules in each compartment of an ice cube tray freeze in layers of interlocked hexagonal patterns, from the outside in. The tight, pure-ice bond building up around the edge squeezes out molecules of any other size (dissolved minerals, gasses, chemicals), so they float around, unfrozen, until they’re jammed into the middle of the cube. The pure-ice part of the cube melts more slowly than the contaminated center, which explains why the cubes in that Pepsi you left on the counter an hour ago are now just hollow, transparent ice skeletons.
Local ice-making companies say that all cube-making machinery also filters the water first, but even if there were impu rities in Mexican cubes, they say, the effect on melt rate would be negligible. So ice by any other name, including hielo, would melt as fast. We consumer boobs may clamor for French or Italian water, but so far we’re not clamoring for a bag of the finest Swiss glace.
Sept. 28 update
And re the melting Mexican ice question, O.B.’s Fred J. Crowe sends a treatise on Alaskans and how they chip their drink ice from glaciers, and maybe Southern Californians probably shouldn’t be running their mouths about frozen things. “Got your ass in a crevasse on this one,” he gloats. Okay, have it your way, Fred. I’d limited my discussion to commercially made ice, since that was the gist of the question; but if you want to talk glaciers, yeah, I agree, the North Pole is melting slower than a bag of cubes from 7-Eleven. In the waning days of the overstuffed ’80s, bars in the lower 48 also touted drinks cooled with 10,000-year-old glacier ice shipped in from Alaska. The ice is so highly compressed that it melts quite slowly. Commercial ice-makers, too, sell a form of compressed ice, made from flake (crushed) ice smashed into little pellets or rods. It has some of the best qualities of crushed and cube ice and is used a lot in salad bars. Happy now, Fred? Good. Another only mildly disgruntled customer.