How Frozen Custard is Made...The Original Iron Lung.
The monstrous metallic machines used to make custard – known to fans as “iron lungs” – churn at a stately pace that introduces little air, or “overrun” as the percentage of air is called, into the mixture, so the finished custard that extrudes from the machine is dense and thick. Spoons stand at attention in a bowl of custard. In contrast, many commercial ice cream makers whip lots of air, as much as 100%, into their product for volume and texture. So a finished pint or half gallon may contain nearly as much air as ice cream.