Immersion Freezer Or Brine Freezer.docx

Immersion Freezer or Brine Freezer In the immersion freezer the product is completely emerged in a tank with a cooled freezing medium which can be chemicals or mixtures with salt or sugar. Immersion method is the fastest freezing method and it is commonly used as a pre-treatment of large products in order to create a frozen layer before the product is exposed to longer freezing time, in order to avoid dehydration. The challenge with this method is that the solution becomes quickly diluted with the product which can change the process speed and efficiency. It is an equipment that adopts a system where the sealed food material is immersed in lowtemperature coolant, such as brine or alcohol, that recirculates and comes in direct contact with the surface of the food package. The high heat transfer coefficient between solids and liquids enables this equipment to cool materials faster than cold air-freezing systems can. The Immersion Freezer is a cost-effective equipment: The fast cooling rate conserves electricity, while recirculation maximizes the use of the coolant. This cost-saving technology adds to the efficiency of the food industry.

Immersion Freezers In immersion freezers the product is immersed directly in, or sprayed with, a cold liquid such as a brine or glycol. The product is usually packaged to prevent crosscontamination between the liquid and the product. Products with irregular shapes are easily handled. Although high rates of freezing can be achieved, these types of freezers are now seldom used except for some fish, meat, and poultry products. The liquid is refrigerated either by circulation through a heat exchanger or by cooling coils and/or a jacket built into the liquid tank. method for food manufacturers to freeze food items, such as poultry and beef, by exposing a food product to liquid nitrogen for a period of 6 to 10 seconds. It is often used to prepare a cooked product for further freezing. The immersion freezing reduces the temperatures on the crust of the item to slow or stop the cooking process, so the product no longer emits steam from the cooked item. It also serves to lock in some of the moisture within the product as it has cooked.

Immersion Freezing To prepare intact cells or cytoskeletons for cryo-electron tomography it is necessary to grow cells on filmed E M grids. The samples must then be rapidly frozen in layer of medium thin enough to avoid ice crystal formation

and also penetrable by the electron beam. This requires an apparatus which allows controlled blotting of the cells in a humid atmosphere to avoid drying before freezing. For our experiments, we have used a semiautomatic instrument developed by Leica Microsystems in collaboration with Guenter Resch of the EM Facility, the Leica E M GP grid plunger. In this guillotine-like apparatus, the EM-grid carrying the specimen is mounted in forceps in a temperature– and humidity-controlled chamber. Subsequently, the major part of the liquid (medium, buffer) surrounding the specimen is blotted off with filter paper, to leave only a thin layer of 50–300 nm. Immediately after blotting, the specimen is plunged rapidly into a vessel containing a cryogen (liquefied ethane or propane). To avoid direct contact of the cells with the filter paper, the grids are blotted only on the backside and a blotting sensor ensures uniform results from one sample to the next. A high yield of well-frozen grids is particularly important when performing correlative light and electron microscopy. The frozen specimens can be stored in liquid nitrogen for long periods of time.