What is that White Film on My Silicone Ice Trays?

Talk to enough cocktail types and eventually the name Tovolo comes up. Not, it’s not the name of a pre-Prohibition bartending genius or an obscure Italian amaro. Tovolo is the international housewares division of ICI USA and it makes, among other things, a nifty silicone ice cube tray that makes dense cubes — actual cubes with equal sides — of ice.

Talk to enough people who use those trays, though, and a common complaint arises. After some time in the freezer, the trays may develop a persistent white surface film.

 The film forms on the interior and exterior surfaces of the trays, is transferred to the ice, and gives an off taste and smell to drinks as the ice melts. There’s even a waxy residue on my tongue after getting Tovolo ice cubes from trays that have the film.

What the hell is this stuff? And how to you get rid of it?

It doesn’t seem to be caused by mineral-heavy hard water (otherwise, we’d likely see it only on the side of the trays, but see below for a contrary finding). It seems, rather, to be some reaction of the silicone itself. One thing that makes me think this is that of all my kitchen utensils, the silicone spatulas — and only the silicone spatulas — develop a different, almost greasy feeling, surface coating. Now, I do keep those next to the stove, so perhaps they attract minute particles of airborne cooking grease that the wooden and metal utensils don’t. When I expand my consideration to kitchen gear more broadly, the Silpat silicone baking sheets acquire that same slightly greasy feel if I haven’t used them some time and I keep those in a closet away from the stove. Both of those films wash off easily with a soap and hot water.

This is not the same film the ice cube trays develop; that all of my silicone eventually behaves oddly is the only connection I’m making. I’m not a chemist and don’t know what’s going on.

So I threw out a question to members of the Cocktail and Spirits Online Writing Group: anyone else notice off-tastes from these cubes and, more to the point, have luck restoring these trays?

Yes, writers noticed the film as well. Not everyone, but several had. There was no consensus on what caused it. Suggestions for restoring the trays ranged from using toilet bowl cleaner (um, pass) and boiling the trays in water to scrubbing them with vodka or vinegar and running them in the dishwasher.

I have tried all those suggestions (well, not the toilet bowl cleaner) and am here to tell you that none of them works. At least, not for very long.

Soaking and rubbing the silicone ice cube trays with vinegar and vodka (separately) initially eradicated all traces of the white film, but it bloomed on each test tray again within a week. I boiled a tray for five minute: no dice. Ten. Same. A twenty-minute boil did nothing to remove or reduce this persistent film.

Finally, I wrote to cookware doyenne Mariella Esposito of Fante’s kitchen supply shop in Philadelphia. She got in touch with a silicone tray manufacturer who wrote this:

We have heard this type of feedback before on the ice trays and have tested them extensively. We test both the original raw material, the catalyst, as well as samples of trays that have been used and been returned to us by customers.

We actually did a chemical breakdown test on this white residue from a tray that we rec’d back from a customer and the result of that test is below. The compound associated with the residue is Calcium Sulfate – meaning basically the residue is associated with the chemicals in hard water. Like a mineral deposit. The minerals from the water calcify and adhere to the walls of the silicone and are then transferred to the surface of the next ice cube to be made.. etc.. etc.. etc..

We have found a dilute solution of vinegar and water to be a great solution. Simply soak the trays in this for about 20 minutes, rinse them and you should be ready to go. Most soap based cleaners can also leave trace amounts of milky residue on the ice trays. You ‘ve seen those old dishwasher detergent commercials where they take the glass out of the washer and it has a white residue on it… viola.

So, there you go. A suggestion that calcium sulfate is at play on at least one tray tested and may be cleaned with vinegar. My guess is that probably does work with some trays. But not mine.

Any chemists out there have recommendations on what else this stuff may be and how to eradicate it?

Otherwise, I’m left with the words of Nathan Lutchansky, a cocktail enthusiast in Pittsburgh:

Yeah, that happens after a while with those Tovolo trays. At that point they're worn out enough that we just throw 'em out and buy new ones. They're pretty cheap.

Goes well with:

• Tovolo sells their trays on Amazon. Despite my questions and frustrations, I do still like their trays. You can find some of their selection here.
• If you'd like to reach out to members of the Cocktail and Spirits Online Writing Group yourself, check out the group's website here and drop in the Mixoloseum chat room on Thursdays for themed nights of drinking, mutual heckling, and frequent visits by brand reps, authors, bartenders, and distillers.
• Fante's Kitchen Wares Shop, one of my all-time favorite cookery stores in the entire United States — and, yes, that's exactly the sort of place I visit when traveling. A sprawling warren of rooms filled with knives, copper pans, mixers, juicers, pepper mills, cake pans, bread baskets, pickle grabbers, meat mallets, food coloring gels, and, yes, ice cube trays.