Preserving food by reducing the temperature. At room temperature or between 5 o C – 60 o C bacteria can double ever 20 mins, so it can be useful to control the temperature of the foods environment to aid in preserving foods. Food storage in the chiller (refrigerator)
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At room temperature or between 5oC – 60oC bacteria can double ever 20 mins, so it can be useful to control the temperature of the foods environment to aid in preserving foods.
Food storage in the chiller (refrigerator)
Chilling food does not kill or stop bacteria but it reduces the rate at which bacteria can multiply, at 4o C bacteria will multiply every 4 hours, this is better than at room temperature.
So the chiller (refrigerator) should stay in the range of 1oC to 8o C. If the temperature in your chiller goes above 5o C, there is a greater chance of rapid food spoilage and bacteria growth, think if you have ever left a bottle of milk out of the fridge on a warm day what happens? If your chiller is below 1o C your food will become frozen.
Cook chilling is exactly that the food is cooked then chilled very quickly. The food must go from being hot to between 0oC - 3°c in 90 mins or less! Factories often use this method in ready meals. These foods have a short shelf life of 5 days, which is more than it would be without chilling. The food must be reheated by the consumer.
Freezing food as a method of preservation
Freezing food causes the microorganisms (bacteria) on the food to become dormant very similar to the way a tortuous will sleep during winter, when the food is defrosted the bacteria will wake up again and begin multiplying. So the freezer is kept between -18o C and -25o C
However freezing causes the cells to form ice crystals as the water content in the food is frozen, when the food is defrosted and the ice turns back to water the cell is left deformed as shown in the picture to the right. This can cause the food to look and/or taste different.
Supper markets and factory's try to combat this by blast freezing their products so the food goes from 0oC to -18o C in about 12 mins this process produces smaller ice crystals which do not damage the cells in the food as fast.
Freeze drying is another method of freezing food which prevents ice crystals from forming in cells while freezing. The freeze drying process usually uses liquid nitrogen to freeze the food and a special machine which applies pressure to the food and the liquid nitrogen, this pressure and liquid nitrogen causes the water in the food to turn to vapour so ice crystals are unable to form as there is no water.