“Showa Freezing Plant of Hokkaido who manufactures ice making machines has developed a manufacturing unit of nitrogen-injected ice and started sales for fishing boats or ice-making plants. Eleven units have so far been sold. The company is going to make further efforts to popularize the nitrogen-injected ice making machine which gives anti-oxidation effects. The nitrogen ice is the first anti-oxidant in the fishing industry.

In the ice making process of the nitrogen ice manufacturing system developed by the company taking three years from 2002, air taken in by a compressor is first brought to a small-type nitrogen PSA having a supply capacity of 360 liter per hour. The nitrogen gas concentrated to 99.999% is injected little by little into fresh water or seawater for bubbling at a water temperature of 3℃ under pressure of 0.3Mpa through a dedicated nozzle. In case of a water temperature of 15℃, it takes about 90 minutes to reduce the dissolved oxygen close to zero, but the time can be shortened to 40 minutes saving 50 minutes at a temperature below 3℃, which is the most suitable temperature to get rid of oxygen molecules. The oxygen driven out at the time of bubbling is thrown out to the atmosphere through the vent on the top of the attached nitrogen water tank, but no recovery of oxygen is done. Then, the purified nitrogen water is refrigerated by an ice making machine at the refrigerant evaporating temperature of -25℃. This technique was patented in February 2008.

The development of ice to enhance freshness keeping capability has long been proceeded and brought out some results like the insoluble seawater ice taking advantage of the low freezing point, the sherbet ice enabling damage-free tight sealing of surface with fine ice and the flake-formed ice for quick cooling using its large surface area. However, all of them have encountered difficulties because of their nature of ultimate easy oxidation.

Therefore, president Wakayama of the company reached the thought to combine the two methods of popular nitrogen injection and stripping in order to remove dissolved oxygen in water with nitrogen. Nitrogen gas of 3600 liter per hour is used to make nitrogen ice of 20 tons per day.”