Crown said the improved processing of edible products within metal cans can be achieved by using beverage-style cans that are better at resisting increases in internal pressure and using induction heating to heat a small amount of water within the can to process the particulate inside it.
The firm said using a “beverage-style can” was beneficial as they are made from thinner metal than food cans, so are cheaper to produce and are lighter so incur lower transport costs.
A particulate product does not typically contain any liquid other than that within the particles themselves, said inventors Lucy Michelle Winstanley, Paul Charles Claydon and Chris Ramsey.
This means the patent is aimed at products such as peas, vegetables and beans, but not soup or spaghetti or beans in tomato sauce.
How it works
The patent describes the volume of liquid provided in the can as being between 15-20% of the internal can volume.
Induction heating may be applied to heat the liquid for no longer than seven minutes and the can wall thickness at the thinnest point on the sidewall of the body may be less than 0.1 mm.
Crown Packaging Technology, part of Crown Holdings, adds that once closed, the metal can may be able to withstand an internal pressure differential of at least four kilopascals (kPa).
The method may comprise agitating the contents of the can during heating by rolling, vibrating, rotating and turning over.
The can may be pressurised with an inert gas before being closed with the lid, and the inventors suggest Nitrogen.
Conventional methods
Current processes involve heating a metal can after it has been filled and sealed in order to process and sterilise the edible product and interior of the can.
“Heating cans using a conventional retort can be relatively slow, as the heat transfer occurs by conduction through the can wall,” said the inventors in the patent.
“It is also inefficient as the retort needs to be heated as well as the can. Likewise, the cooling of the can after heating may also be slow if the retort has to be cooled down too.”
They identified alternative methods such as cans being induction heated at super-atmospheric pressure in order that they are able to withhold the increase in internal pressure in an attempt to reduce the time for which the contents of the can are heated.
“The present solutions for heating and processing food products in closed metal cans are inadequate for a number of reasons, including inefficiency of heat transfer to the product, wasted energy cost of heating things other than the edible product, technical difficulties with overcoming internal pressure within the can during heating, high water consumption, the need to heat retort up to temperature, and also slow cooling times.”