Shaken, not stirred
"Shake it," say researchers at Nofima, who are discovering the untold benefits of shaking in sterilisation and pasteurisation. Heat treatment using horizontal agitation, so-called shaka technology, produces more rapid heat penetration and improved sensory qualities.
For the past year, Dagbjørn Skipnes and his fellow research scientists have carried out hundreds of experiments and tests with their newest autoclave, the Shaka autoclave. This technology ensures a far more efficient production process and opens the way for new innovations in both sterilisation and mild heat treatment.
The autoclave technology has been used for sterilising foods for more than 150 years. The food was filled in cans and placed in a static autoclave where the cans were exposed to high pressures and temperatures. Food is pressure cooked in an autoclave, but nutrients stay inside the packaging and the product is sterilised in a natural way without chemicals, provided that the core of the food is sufficiently heated. In order to achieve sterilisation, products must be subjected to 121°C for three minutes, while mild heat treatment (pasteurisation) is achieved at 70°C for two minutes.
All autoclaves were static until the 1950’s, when a rotary version was developed. With the shaka autoclave the technology has taken another giant leap ahead. Its horizontal agitation technology has many advantages, such as speeding up the heat treatment process and applicability to far more product types than before.
Fish soup in a tenth of the time
“We have carried out a number of tests on a fish soup containing pieces of fish, and with the shaka treatment we can save up to 90% of the time (from 70 to 7 minutes)! In addition to this enormous improvement in production efficiency, the soup tastes far better after shaka treatment than after pasteurisation in a static autoclave,” says Dagbjørn Skipnes.
A rotary autoclave is not an alternative for products containing pieces of food, as these can disintegrate or be thrown out on the edges, losing the stirring effect. A rotary autoclave works best for products with an even density and has a lower maximum speed limit than horizontal agitation.
Rotary treatment also necessitates a headspace of around ten per cent, which is a major disadvantage for many food producers.
“We have tested the shaka autoclave with headspaces of two and four per cent, and both work well. We are now starting experiments with no headspace at all,” says Skipnes.
Useful for the industry
Nofima is the only research institute owning a shaka autoclave. During this first year of experience with this new technology, Dagbjørn Skipnes and his fellow research scientists have carried out hundreds of experiments. They have defined optimal agitation frequencies and speeds depending on food viscosity and various packaging systems.
The results of these experiments will be of great use to companies who are considering implementing the shaka technology.
“Producers are coming to us because they are curious about this new technology. They wish to identify whether a shaka autoclave could have a positive effect on their products, and they don’t want to spend unnecessary time testing the right levels of heat treatment,” says Skipnes.
A shaka autoclave is more expensive to purchase than both the static and rotary autoclaves. The cost is about twice as much as a static autoclave and 50% more than a rotary autoclave. But the increased investment can be covered through a far more efficient production process. Both a shorter production time and the possibility of less headspace also make the production process more environmentally friendly.
With the shaka technology, autoclaves can now be used on products that were unsuited to the previous autoclave methods. One such example is dairy products, where the heat treatment process is too long with both static and rotary autoclaves. With a shaka autoclave, however, the heat treatment time has been reduced so dramatically that dairy products that are today packed aseptically can probably be treated with shaka technology. In this way, producers can avoid an aseptic production line and produce smaller batches.
A greater variety in potential packaging types is another benefit of the shaka autoclave.
“Using agitation we can use far larger packaging than before, as it doesn’t take as long for the heat to penetrate to the core of the food. We have tested the shaka autoclave on rectangular plastic bowls, round plastic bowls, flat tins such as those used for sardines (1/4 dingley), round cans as well as large and small plastic cups. All of these packaging types work very well, and opens the way for using autoclave treatment for completely new product types,” concludes Skipnes.