Custard’s overrun, however, should hit at less than 25%, according to Linscott of Gilles Frozen Custard. “Quality custards have less air whipped into them. Some places go higher, but I don’t know many that go much lower [than we do],” he says. The end result: a dense solidity that ice cream wishes it could claim.
These machines also make custard terrifically fast. At Gilles, that means the finished product is ready less than twelve minutes from the time the mix is poured into the machine -- although the exact time varies by flavor. Recipes that contain more sugar take a little longer to finish (which makes sense when you think about how much harder it would be to freeze an ingredient like sugar versus, say, cream). The iron lung’s quick-freeze method is also key to keeping the product’s ice crystals small, which is what gives custard its iconically silky, super smooth texture.
Next, the custard is sent down a chute into a dipping freezer, where it’s ready to be dished up. Because it’s served as soon as it’s made, the temperature of the custard is higher than that of scooped ice cream, which has to be kept in a freezer before serving. This makes for a softer product, similar to soft-serve ice cream -- although thanks to the low overrun and small ice crystal formation, you end up with a completely different, infinitely more luxurious texture.