Food Preservation using Pressure Cooker

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      It can be possible to preserve food with a shelf life of up to one year with our ordinary pressure cooker. This method of food preservation does not require refrigeration. Microbes already present in the food and coming from surrounding environment spoil the food. In this method, we kill the microbes in food, by applying sufficient heat for enough time as well as to prevent microbes entering into, by utilizing airtight nature of a pressure cooker.
      The things required for food preservation in this method are a pressure cooker, perishable food, and a heat source. First, check whether the pressure cooker is airtight by blowing through its steam valve. If air does not escape through the sides of the lid, we can confirm that it is airtight. Place the food material inside the pressure cooker with sufficient water for cooking about 5 minutes. Place it above the heat source. When steam abundantly comes through the steam valve, put the weight and cook for at least 5 minutes. If we put weight in the beginning, the atmospheric air already present inside the pressure cooker does not come out, which will reduce the temperature initially due to the low specific heat of air. After 5 minutes of cooking, avoid removing and disturbing the weight. Place the pressure cooker in an undisturbed place. The contents inside of the pressure cooker are in a sterile condition until and unless we remove or disturb the weight. A negative pressure is formed inside the pressure cooker when it is cooled after heating. So even slight disturbance of the weight leads to atmospheric air rush into the inside of the pressure cooker, which may contain viable spores of microbes. Open the lid only at the time of consumption. Sterility is lost, when the lid is removed, so refrigeration is required for further preservation as like normal food items. If, at the time of opening the lid, the food shows any indication of spoilage, such as bad smell, distaste or air bubbles; discard the food. It indicates that initially the food had not been sterilized, microbes entered inside through disturbance of weight or lid or the pressure cooker was not airtight.
      The cooking or sterilization time depends upon the type of food materials used. In order to get sterility in 5 minutes of cooking, food should be properly ventilated. Heat will not penetrate into the center of large blocks of food items such as blocks of dough or meat. In such situations, more than an hour of cooking may be required.
      This procedure can be used in our day to day cooking. If we cook the food in the pressure cooker at night and not remove the weight, the sterile condition might be present inside the pressure cooker and we can get fresh food in the morning. The moment we open the lid, microbes enter the food and after some time start to multiply. By avoiding the removal of the weight at night, we are actually increasing the shelf life of the food to a few hours more.
      A sterile condition actually forms inside the pressure cooker after cooking and no microbe from atmosphere enter inside the pressure cooker because of its airtight nature. The airtight nature further prevents escaping of moisture from the contents inside of the pressure cooker. Sterilized food items are available in the market in aseptic packages: its manufacturers usually say their products should be used within 3 to 12 months from the date of manufacturing, depending on the food materials. The same time frame can be applied to the food preservation by using this method. Usually, we do not require preserving food for more than a month. After the ‘best before’ date the food is edible, but sometimes there would be a change of flavour due to chemical processes. There is a chance that food materials with high acid content may corrode the pressure cooker.

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