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Freezing is a common food preservation method that is used by almost everyone, gourmet chef or not. It works with lower temperatures and reaction rates, preventing the proliferation of bacteria and other microorganisms. The early concept of freezing food was brought about by Clarence Birdseye in the 1920's thanks to his desire to get fresh food, whatever season of the year it was. His observation of how fish were preserved in the Arctic has lead to modern day freezing. This common kitchen technique retains nutrients in food as well as provides an avenue for quick meals.
However, in the world of molecular gastronomy, freezing does more than just preserve food. It serves as cooking technique that provides a unique way of presenting dishes. Better known as flash freezing, this modern cuisine technique involves the use of very low temperatures to quickly freeze food. First used in El Bulli restaurant, it has lead to the creation of many diverse dishes.
This technique of freezing allows liquids to be frozen completely or partially. As a result it is possible to create fluid filled frozen dishes with solid outer shells. The process of rapid freezing is done with the use of a cryogenic system. Liquid nitrogen is a common tool used in the process of flash freezing due to its extremely low temperatures and cooling properties. The liquefied gas reacts with the food that it comes into contact with and results in the formation of small crystals that solidifies food without affecting taste.
Serving as a coolant, liquid nitrogen is not used as an ingredient so it is not ingested by diners. In cases where the liquid nitrogen is mixed into foods such as cream, it quickly evaporates into the air. Due to the properties of liquid nitrogen, care is needed when using it for freezing. Special equipment such as an anti grill or anti-griddle can be used alongside this modern cuisine cooking tool.
Those who employ the use of freezing in modern cuisine will observe a number of benefits brought about by this technique. The following are just some of the ways that this technique can be used to enhance dishes and dining experience.
There is no doubt that the use of cold temperatures for cooking brings about a whole new approach to food. As previously mentioned, it is possible to create dishes which are solid on the outside and liquid on the inside. This is a different way to serve food be it for desserts, appetizers, soups, salads or even a main course. Aside from this, freezing makes it possible to create intricate decorations that can be used as garnishes for dishes. The employment of freezing can also be observed in food presentations where "smoking" dishes are served.
With the different characteristics of frozen dishes it becomes possible to bring together different textures. Diners can experience eating something that is both solid and liquid at the same time, creating a different experience in the mouth. More than just being solid, the shells of frozen food may be crunchy and delicate. On the inside liquids may be creamy, rich or light and flowing. Flash freezing can also be used to create fine powders or to quickly breakdown food. Frozen ingredients can be delicate and will shatter quickly under force producing pieces or even a fine powder.
While the use of liquid nitrogen does not directly affect the taste of food, the state of being frozen may enhance flavor. The small crystals formed during the process of flash freezing do not affect food quality or nutritional value. In turn, this keeps food properties intact and intensifies both smell and flavor in dishes.
In the kitchen flash freezing is done mainly with the use of liquid nitrogen. As the name implies, this is nitrogen gas which has been liquefied through the process of fractional distillation. It is presented as a clear liquid without any color. Classified as a cryogenic liquid, it brings about rapid freezing upon contact with tissue. Under normal atmospheric pressure liquid nitrogen has a boiling point between -198 to -196? C. Exposure to ambient heat or contact with any object warmer than it is will cause this liquefied gas to boil.
The instantaneous boiling will result in the encompassing of objects in nitrogen gas and forming a gas cushion. This is also otherwise known as the Leidenfrost Effect. Liquefied nitrogen is poured directly onto food or into a bowl. Contact with the food or the container will cause the liquid nitrogen to boil and produce a sort of gas steam as it evaporates. This then envelopes the food allowing nitrogen gas bubbles to form and crystallize. From this steam of gas microcrystals are formed and solidify food.
Under normal freezing circumstances, water contained in food form the ice crystals. These large crystals tend to damage the cell membrane of foods resulting in altered taste, texture and nutritional values. Freezing with liquid nitrogen produces crystals which are relatively smaller, therefore preventing any damage to the cell membrane. This is what keeps food properties such as consistency and taste intact even after the freezing process. The speed used for freezing food plays a role in the size of crystals formed. The quicker the process, the smaller the crystals and the less damage to cells there are.
It is common for food frozen with liquid nitrogen to be very cold. Serving this right after preparation is not recommended. Dishes should be allowed to warm a bit in order for temperatures to increase and for any remaining liquid nitrogen to completely evaporate.
As stated earlier, liquid nitrogen is a common component in cryogenic cooking. However, rather than being an ingredient it is considered to be more of a tool. Although it can be mixed in directly into food, it will evaporate and leave no traces afterwards. It is non-toxic and does not have any scent or color. Since it works as a coolant it makes food colder or freezes it, then evaporates afterwards.