When thinking of cryogenics, most people think of the science fiction fantasy whereby billionaires freeze their decaying bodies in liquid nitrogen in the hope that technology will catch up and allow them to live forever.
In real life, cryogenics has many, less dramatic purposes, albeit important ones – including the freezing of foodstuffs.
There are two standard methods of freezing foods at an industrial scale. One is mechanical, and the other is the aforementioned cryogenics.
The mechanical method involves using a chemical refrigerant such as CFCs or ammonia, which is used in a closed cycle. The system moves large volumes of air to freeze the product. It cools the air like a refrigerator, but, is of an industrial size with a bit more grunt in its engine.
A cryogenic system is different. It uses liquid nitrogen or liquid carbon dioxide to freeze the product. It has direct contact with the product either as droplets of liquid nitrogen, or solid particles of carbon dioxide (dry ice)because carbon dioxide cannot exist as a liquid at atmospheric pressure.
Air Liquide is one company that specialises in cryogenic freezing and is at the forefront of a technology that has been around for more than 50 years.
The company’s senior international expert in food processing, Aron Segal, knows that cryogenics is a niche market, but an important one. There are benefits and issues with both mechanical and cryogenic freezing. However, cryogenics is not utilised as much as it should be, especially for those people that don’t have a massive amount of money to invest in capital.
“When it comes to mechanical freezing, the operating costs are strictly dependant on the price of electricity,” said Segal. “But, you have a high capital investment for the equipment. There is little operation flexibility with the mechanical freezing system because you basically set your set points in the freezer and so you have very little movement of that temperature.”
It also takes a longer time to install a mechanical freezer system than a cryogenic one. There is a lot of maintenance required to keep the mechanical system in good working order.
“Against that, you have cryogenic freezing, which requires a lower initial investment because the equipment is smaller, it operates colder and can be rented,” said Segal. “There’s very low maintenance and no compressors. There is just injecting a fluid into a freezer and then exhausting the gas.”
Cryogenics is also very fast freezing because products are frozen at a set point, such as -60, -80, -100 or -120˚C. It is rare for a mechanical freezer to operate below -40. And because cryogenic freezing is faster, it requires far less floor space because you are moving product through quicker. Then there is the science behind this type of freezing system.
“You get quality product because the faster you freeze something the smaller the ice crystal size,” said Segal. “The larger the crystal size, the more likely the product is going to thaw out not looking exactly like it did when you froze it, which when it comes to vegetables and fruits, can be a problem.”
Then there is moisture loss, which can be a big issue when manufacturers are selling product by weight and they lose four or five percent of that product’s weight in the freezing process. It’s a big cost to the bottom line. Because cryogenics is faster, there is less loss.
Segal said that cryogenics are also ideal for those that are just starting out a business mainly because of the aforementioned lower capital outlay as well as a lack of space. Not only that, but if the business is volatile, a company could be left to the whims of its clients’ fickleness.
“If you have invested in a mechanical system and you lose an important customer in two or three years, you’re stuck with that plant,” he said. “If you opt for cryogenics, with the correctly sized cryogenics freezer, it takes up far less floor space and you can install it overnight. You can press the button the next day. And if you lose the market, you’re not stuck with high-end capital equipment.”
Segal also said that cryogenics is capable of targeting specific aspects of a product, which again, is another feature it has over its main rival in the space.
“We’ve developed a range of equipment to do other things, not just simply freezing produce. We can crust freeze and crust harden,” he said. “Let’s say your end product is sliced ham. You have these large portions you want hardened a bit to make it easier to slice. With cryogenics you can get a firm outer surface that you don’t get with mechanical freezing because it will take a long time. Therefore, you’ll get more efficient slicing and far
less wastage. The slices can fall nicely on the conveyor where they can go into a qualified atmosphere packaging system.
“Another example is if you’ve got small particulate products like pizza toppings. To freeze them mechanically would be difficult. You’d probably have to do it in bags because you probably wouldn’t like it on a conveyor belt. Cryogenics has systems that can handle particulates so they don’t come out in a frozen clump. They come out free flowing.”
Segal gives another example of where cryogenic freezing would be ideal – desserts. A manufacturer can harden the main part of the product in the cryogenic tunnel – not fully freeze it, but partially freeze it. Then they can put a topping on it and put it through again and freeze the topping without intermingling with the lower component. This is especially important when different components of a product have different freezing points, or react in different ways to certain temperatures. Segal said that it is part of Air Liquide’s brief to work with clients on how cryogenic freezing can help them make sure their business reaches its potential while guaranteeing safe operations.
“Niche products are where we find our current market,” he said. “When people are trying to create these products, it is cryogenics that helps them. It’s not just about putting products in and freezing them, there is the value-added aspect. When we identify enquiries, we have to understand exactly what our client is expecting from the freezing process. We know very quickly whether cryogenics is going to be a process that supports their cost structure, and how suitable it is for their business or not.”