The secret to stable, silky ice cream
‘Dr Freeze’, who leads an ice-cream course at UCC, is unravelling ice cream’s structure with sophisticated tools and improving its shelf life
Premium ice creams contain up to 15 per cent fat, which is well-dispersed so you feel lubrication but not chunks. Photograph: Thinkstock
Toasted Irish oats, lemon curd, sea salt, Kieran’s cookies, Dingle gin and Kerry cream vanilla: these are just some of the mouth-watering ice-cream flavours to choose from in a Dublin scoop shop this summer.
While adding a few days of sunshine and warm weather is a help, taste is crucial for lovers of ice cream, and so too is texture. You need to balance air, fat and ice just right for a silky-smooth combination. It’s a complicated subject that has fascinated Doug Goff, a professor at University of Guelph in Ontario, Canada, whose father ran an ice-cream shop in Nova Scotia. Goff leads a short ice-cream course at University College Cork.
“Cream, milk and sugar would be the primary ingredients, and then stabilising agents to maintain a good shelf life and keep good texture,” says Goff. Ice crystals must be tiny; if crystal size approaches a 10th of a millimetre, we can detect it on our tongues, and it feels coarse.
The secret of silky-smoothness is speed: whip and freeze the ice cream quickly so only tiny crystals and small air bubbles form. “When ice cream is of high quality, you put it in your mouth and it feels cold and creamy but is also smooth,” says Goff, who has been dubbed Dr Freeze. By volume, a typical scoop of vanilla is 30 per cent ice, 5 per cent fat, 15 per cent sugar solution and 50 per cent air.
Ice cream is whipped to foam for that soft texture. “Without any air, it would be just like an ice cube,” says Goff. Fat helps to stabilise the air bubbles by coating their surface. Tiny globules of fat melt in your mouth to give that creamy feel. Premium ice creams contain up to 15 per cent fat, which is well-dispersed so you feel lubrication but not chunks. These use dairy fats and have less air than cheaper options, sometimes just 20 per cent.
Murphy’s of Dingle
Kieran Murphy, who set up Murphy’s of Dingle with his brother Seán, says they keep their recipes simple and use Kerry cows for their milk. They use carrageenan from seaweed as stabilisers. “We add cream, egg, milk and sugar to make custard, day one. Then, on day two, we freeze it,” he says. Their use of cream and egg is a hallmark of premium products.
Luxury brands such as Häagen-Dazs and Ben & Jerry’s have a high fat content derived from milk. Most regular tubs you pick up in a supermarket also have non-dairy-based fats, usually palm or coconut oil, which solidify at the right temperatures and help keep the price down.
UCC’s David Waldron is a dairy scientist who gives lessons in how to make ice cream. He makes batches in a small-scale facility. Premium ice creams use egg as a stabiliser, which is not so good in the frozen environment, he says.
“If you thaw, and then put it back in the freezer, you will see crystals grow. Egg is wonderful for flavour and thickness, but the moisture in those ice creams can start to move, and they get crunchy after a while,” says Waldron.