A fancy or a fallacy?

Does this new way of making ice cream really save energy?

Ice cream is not the epitome of healthy food, yet can be made and served in a more environmentally-friendly way. Recently a US-based ice cream company says its liquid nitrogen ice cream does not need a freezer to survive, which saves much energy. This trending way of making ice cream has already made its debut in Hong Kong.

Unlike most frozen dessert stores where ice cream stays in refrigerators for customers to pick up, local ice cream company Lab Made Ice Cream only sells its products on a purchase order basis.

Not that its ice cream is tailor-made with snob appeal, but a substance called liquid nitrogen makes everything different.  

Liquid nitrogen is the liquid state of nitrogen, a gas forming about 80 per cent of the earth's atmosphere. This odourless and colourless component of air will be liquefied at an extremely low temperature of around -196 °C, Dr Stephen Chow Cheuk-fai, a science associate professor at the Hong Kong Institute of Education says.

This chilly liquid often serves as a cryogenic fluid that can cause immediate freezing on contact with living tissues. In the same way, it makes ice cream freeze within 30 seconds, according to Mr Ronnie Cheng Hong-wang, the owner of Lab Made Ice Cream.

To solidify ice cream paste, one just needs to mix it extensively with liquid nitrogen in an electric blender. "It will take you as long as 30 minutes if an ice cream machine is used instead," Mr Cheng said.

Mr Cheng needs nothing but a special container to store liquid nitrogen. And containers of this kind can be found in many laboratories.

"They work like vacuum flasks which can keep the liquid nitrogen at ultra-low temperatures," Dr Chow said. Thanks to its closed-system design and high pressure inside, the tank is able to prevent liquid nitrogen from evaporating without consuming energy.

Given that Mr Cheng only makes ice cream after receiving orders, the shop's biggest electricity guzzlers are only several light bulbs and an air-conditioner.

Ostensibly the US ice cream company is on a seemingly concrete ground to make the claim that its ice cream saves a lot of electricity. Yet Mr Cheng does not agree, although this can become a key selling point of his liquid nitrogen ice cream.

"I am not saying it must be wrong. But I believe the company itself is not sure if the claim is right or wrong," Mr Cheng told The Young Reporter. "It is true that fewer ice cream machines are used. But producing liquid nitrogen also uses energy. It is just that the consumption process takes place in the nitrogen factory instead of my shop."

Liquid nitrogen is produced, Dr Chow says, by putting nitrogen gas in an extremely cold medium such as liquid helium, the temperature of which is as low as -269 °C. An alternative way is to increase pressure of a fixed volume of gaseous nitrogen.

Both methods, however, require a huge amount of energy to compress either gaseous helium to liquid helium or gaseous nitrogen to liquid nitrogen by an air compressor.

"Energy is consumed as long as something freezes, no matter it occurs in a refrigerator or an electric blender with liquid nitrogen inside," Dr Chow said.

Liquid nitrogen is commonly used for the storage of blood and cells, as the extremely low temperature can prevent the growth of bacteria and spoilage of tissues. Besides, scientists use liquid nitrogen for experiments which must be conducted at a fairly low temperature.

When it comes to using liquid nitrogen to make ice cream, scientist Dr Chow has some misgivings. "In my opinion, there is no need to make ice cream at a temperature of -196 °C. It is a waste of energy," he said.

Reported by Natalie Leung

Edited by Ruby Leung