Six Quarts, Back Steps, Saturday ONE HAND ON THE CRANK · ONE HAND ON THE LID

What the salt is for

It is not that salt is cold. Salt is room temperature in the box, same as the box.

Plain ice in a bucket melts at 32°F and then refuses to go one degree under, because the melting is eating all the heat and nothing is left over. Put salt in and the melting point drops — the ice has to keep melting well below 32°, and every bit of melting pulls heat out of the can. A properly salted bucket parks around 10°F. That's the whole trick, and it's the only trick.

Marguerite says the leaflet says one part salt to eight parts ice, by weight, and she is not going to say it again.

What the dasher is for

Not stirring. The middle of the can is fine on its own. The freezing all happens against the tinned wall, where the cold is, and it builds there as a film a few thousandths thick.

The dasher's scraper blade rides that wall and peels the film off into the batch. Peel it fast enough and it goes in as a fog of tiny crystals. Let it sit — stop cranking, go get a drink — and that same film keeps growing on itself, one crystal onto the last, until you scrape off gravel.

Big crystals are the entire difference between smooth and sandy. Same custard. Same afternoon.

Why steady beats fast

Crank like a maniac and the batch just sloshes around with the blade instead of getting cut by it. You outrun the scrape. Meanwhile air won't fold in at a gallop either — the overrun, the whipped-in air that makes six quarts of custard into six quarts of ice cream instead of five, only builds in a middle band of speed.

Too slow and the film sits. Too fast and nothing gets scraped clean. Somewhere around a steady forty to seventy turns a minute the blade actually does its job.

Stiff is the finish line

When the handle starts fighting you, that is not the machine breaking and it is not a reason to quit. That's the batch getting thick enough to resist the blade — which is the only honest report you get from inside a sealed can.

The last thirty revolutions are the hardest and they're the ones that matter. Quit at "kind of hard" and you get soup with a chill on it.

The hole in the side

There's a drain hole punched through the bucket above the bottom hoop. Melt has to run out of it. If it plugs with salt slush the brine climbs, and once it climbs past the can lip you get brine in the custard, which is unfixable and tastes like the harbor.

Poke it clear with a stick. Keep poking it. It plugs about every six minutes.

And then you leave it alone

Pull the dasher, scrape it into the can, cork the hole in the lid, pack the whole thing back under salt ice with a feed sack over it for an hour. It's soft when it comes off the crank — the hardening finishes with no blade in it at all, so nothing gets stirred and nothing coarsens.

Also it means the dasher is free, which is the only thing anybody is negotiating about at this point.