杏吧原创

IN THE staff canteen at the Ice Cream Research Unit, there are no prizes for
guessing what鈥檚 for pudding. The dessert counter is a freezer filled with ice
cream of every description. Just help yourself.

The unit, to the north of London, forms part of a research centre owned by
the Anglo-Dutch company Unilever. Though better known for making soap powder,
Unilever is also the world鈥檚 largest ice cream producer. This is where new
generations of the cool confection are conceived, manufactured on a small scale
and tested on human guinea pigs.

Unilever is coy about the details. 鈥淲e have several ongoing programmes,鈥� says
Don Darling, the chemist who heads the unit. But you can be sure that next
summer鈥檚 ice lollies and ice creams are already being licked and sucked by a
lucky group of highly trained tasters.

Here, the study of ice cream is a science. The simplest ice creams are made
from a frozen mixture of water, cream and sugar, but the chemistry and physics
of the resulting substance is hugely complex. Ice cream is both an emulsion and
a foam: an emulsion because it is a mixture of fat and water, like mayonnaise,
and a foam because it is aerated like whipped cream or the head on a pint of
beer.

Through a microscope, ice cream is a crazy paving of ice crystals and air
bubbles cemented together by fat or separated by pools of gloopy, sugary water.
Much of the work at the unit is devoted to working out how this minuscule
landscape relates to the everyday world. Somehow, the qualities of ice
cream鈥攖hings like taste, 鈥渕outhfeel鈥� and scoopability鈥攄epend on this
microstructure and its components. Exactly how, nobody yet knows.

Darling and his colleagues are hard at work trying to find out. The unit is
replete with researchers studying the structure of ice cream using electron
microscopes, nuclear magnetic resonance techniques and optical microscopy.
Donning a white paper coat and hat, Darling darts into the clean area of the
unit. While a small group of food scientists watch eagerly, their latest
creation, a white froth with the texture of viscous eggnog, pours from an ice
cream machine into a large bucket. 鈥淭his is where we test new kinds of
manufacturing techniques,鈥� says Darling.

One of the unit鈥檚 present goals is to make ice cream and water ices more
refreshing. To those in the ice cream world, refreshment breaks down into four
factors: appearance, smell, taste and oral sensation. Darling and his team are
focused on improving smell and oral sensation. In future, ice creams and water
ices will smell more strongly of refreshing flavours, such as lemon, and may
even give you the sparkling sensation of a fizzy drink.

Neither task will be easy. 鈥淚t is already possible to make water ices fizzy,鈥�
says Deryck Cebula, a chemical engineer at the research centre. 鈥淏ut not yet in
a way that increases refreshment.鈥� One way is simply to add sodium bicarbonate
and citric acid, the active ingredients of sherbert. But these produce a frothy
fizz that is a far cry from the refreshing sensation of carbonated drinks.
Another is to add popping candy, small lumps of crystalline sugar that explode
on the tongue. 鈥淏ut this adds no contribution to the sensation of refreshment,鈥�
says Cebula.

Darling and Cebula鈥檚 preferred approach is to store carbon dioxide in the
frozen structure of ice so that it bursts forth as the ice melts in the mouth.
This is easier said than done, as anyone who has frozen a can of carbonated
drink will know. As the liquid freezes, it doesn鈥檛 lock up the carbon dioxide,
but forces the gas into the small space at the top of the can. Opening the can
releases the pressure, and the gas and any liquid left in the can squirts
everywhere.

Sparkling ices

But there is another way to store carbon dioxide in ice. When water molecules
freeze under pressure, they form shells that trap the carbon dioxide within
them. These structures, called clathrates, are stable at atmospheric pressure
and release their cargo of carbon dioxide only when the ice melts.

On the face of it, clathrates sound perfect for the ice cream industry, but
unfortunately they can鈥檛 yet produce that all-important sparkling effect. 鈥淚t鈥檚
more like a burning sensation,鈥� says Darling.

Unilever learnt this lesson the hard way. It designed a flavoured water ice
complete with clathrates, and sold it on the European continent. But market
research showed that people disliked the fizzy sensation, so the company had to
reduce the lolly鈥檚 load of clathrates. Cebula picks up a carton of redesigned
product, called Blizz, and spoons a portion onto a tasting plate. 鈥淭ry that.鈥�
The fizz is so light that it is difficult for the untrained tongue to pick it
out. But as the portion melts in the dish, the clathrate particles are clearly
visible as small white fizzing lumps in the coloured liquid.

This is part of the problem. Clathrate particles are relatively large and
take time to melt. So they continue to burn as they are swept round the mouth.
What Darling would like is to make clathrate particles smaller, so they give up
their carbon dioxide quickly. This should mimic more closely the bubbles that
form in liquids. But small clathrate particles are not as stable as big ones.
Before other sparkling water ices hit the streets, Darling鈥檚 group must work out
how to improve their stability.

Unilever has already made fast progress in another area. Two years ago in
Britain, Europe and Australia, it launched Solero, an ice cream on a stick with
a fruity ice coating which is noticeably more aromatic than other ice lollies.
鈥淲e鈥檙e rather proud of that,鈥� says Darling.

Smelly molecules are volatile aromatic compounds that evaporate easily.
Because of this they tend to disappear into the atmosphere before they鈥檝e had
the desired refreshing effect on the consumer. 鈥淭here is no problem making
low temperature aromatic compounds. But keeping them in is the difficult bit,鈥�
says Darling. This is why most ice cream produces very little smell.

Unilever has licked this problem by using highly concentrated fruit puree in
the coating, effectively packing in huge numbers of smell molecules. 鈥淚f you
consumed it at ambient temperature, it would taste awful because it is so
concentrated,鈥� says Darling. By using methods like this, he predicts that the
next generation of ice creams will be much smellier than they are today.

As Darling removes his paper coat and hat, it is tempting to describe him as
a kind of real life Willy Wonka. But there is nothing fanciful about Unilever鈥檚
approach to ice cream. Rather disappointingly, the science of ice cream turns
out to be a serious business.