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.
Air and gums
The wider industry uses more air and gums rather than eggs to cope with temperature variations. Each time ice cream warms up a little during distribution, water melts and moves around. Guar or locust-bean gum can be added to slow this down. “These [gums] trap moisture and stop it moving around, because when water moves around it refreezes on to larger ice particles, and they grow and get crunchy,” says Waldron.
The sooner ice cream is consumed the less need for additives and stabilisers that can affect taste and texture.
Artisans continue to innovate with flavours. This year Goff has enjoyed blue-cheese ice cream in a Cork restaurant; Guinness and brown bread ice cream in Ireland; wasabi in China; and chocolate with spicy peppers in Mexico. One of his students in California, is making Chardonnay, Sauvignon and Pinot Noir ice cream.
“Sea salt is the one that intrigues people the most,” says Graham Murphy, manager of Murphy’s in Dublin. “We make the salt ourselves, collecting Atlantic seawater and boiling it down.”
Goff has helped to unravel ice cream’s structure using sophisticated tools such as electron microscopes, thereby improving shelf life.
Italian ice cream is increasingly poured from a bucket into an ice-cream machine; fewer Italian shops make their own. It makes perfect business sense. Fresh ice cream is still being made in some places in Ireland. And sometimes we even get the weather for it.
The Science of Ice Cream by Chris Clarke is published by the Royal Society of Chemistry. Ice Cream by H Douglas Goff and Richard W Hartel is published by Springer
TRY THIS AT HOME: BE SURE TO EAT IT FRESH
You can make ice cream at home and add great flavours, says Doug Goff, the Canadian ice-cream scientist who leads a course on the subject at University College Cork. But the biggest limitation is the machine. “The machine is whipping and freezing at the same time, creating small air bubbles and really small ice crystals,” he says. This takes 15-20 minutes on a home device, whereas industrial machines can whip it up in a minute. Because the DIY kit is slower, you end up with larger ice crystals and air bubbles, and that limits texture quality.
“People can still make great ice cream at home, but eat it fresh,” says Goff. Don’t store it for the next month, because it will go hard and coarse really quickly.
“Walking the streets of Italy, and tasting some of the gelatos, is a tremendous pleasure,” he says.
Many aficionados see Italian gelato as the pinnacle. But why is that?
“The sugar content is normally a bit higher, and that lowers the freezing point of ice cream and keeps it rather soft and sticky in consistency rather than firm,” says Goff.
His short UCC course on the science and technology of ice cream, which has run every two years since he took a sabbatical in 2004, has attracted students from Europe, South America and New Zealand, from large and from small companies. It has helped Irish companies too.