Continuous freezer

Surface crustation is caused by sucrose crystallization. It is characterized by hard white spots on the surface. It is remedied by the use of corn sirup solids and larger levels of hydrocolloids. During freezing in a continuous freezer there is ice separation caused by centrifugal separation of small ice crystals. Increase in mix viscosity by use of hydrocolloids inhibits this action. 

The protein ioad increases in the presence of hydrocolloids. In the presence of additional emulsifiers a very effective desorption of protein takes place during whipping and freezing in the ice cream machine. Effective protein desorption is facilitated by the increased viscosity of the mix due to increased surface shear forces, which makes the ice cream continuous freezer work better. 

More than 50% water is converted into ice crystals in ice cream at -5°C to -6°C which is the common drawing temperature for correctly operated continuous freezers. This portion of the water freezes very rapidly, often in less than one minute. Fast freezing induces the formation of small ice crystals, a critical prerequisite for smooth ice cream. At slightly higher temperatures (such as -4°C which is the common drawing temperature for batch freezers), less than 40% water is frozen and the freezing time will be longer. This is one of the reasons why ice cream frozen continuously is smoother in texture than batch-frozen products. 

Partial freezing in the freezer. Ice cream mixes are frozen in continuous freezers applying mechanical agitation and large temperature differences to achieve as small as possible ice crystals. The mix enters the freezer after the required amount of air was injected. Given that exit temperatures are normally not below -3.5 to - 7°C, only part of the water becomes frozen. 

Containerized ice cream is hardened on a stationary or continuous refrigerated plate-contact hardener or by convection air blast as the product is carried on a conveyor or through a tunnel. Air temperatures for hardening are —40 to —50° C. The temperature at the center of the container as well as the storage temperature should be <—26°C. Approximately one-half of the heat is removed at the freezer and the remainder in the hardening process. 

Continuous, plate and air blast freezers for ice-cream Low-temperature brine for lollipop freezing... 

Figure 17.2 Continuous ice-cream freezer (Courtesy of Aifa-Lavai Co. Ltd)...

To obtain a crystalline product, a solution of the residue in 30 ml. of benzene containing a few drops of triethylamine (Note 4) is placed in a 250-ml. Erlenmeyer flask, heated gently on a steam bath, and diluted with 150 ml. of hexane. Heating is continued for about 5 minutes (Note 5), after which the solution is allowed to cool to room temperature, seeded, and put in a freezer at —15° for at least 5 hours. The resulting solid is collected by suction filtration and washed with cold hexane. After vacuum drying, 5.8 g. (94%) of light cream-colored crystals, m.p. 75-77°, is obtained. 

Several variations of the solvent removal technique were developed (6,7). For the PCPP-SA, 20 80, M = 16,000, microspheres were prepared as follows 1 g polymer was dissolved in 1 ml methylene chloride, drug or dye was suspended in the solution, mixed, dropped into silicon oil containing 1-5% of Span 85, and stirred at a known stirring rate. Stirring was done using an overhead stirrer and a three-blade impeller. After 1 hr, petroleum ether was introduced and stirring was continued for another hour. The microspheres were isolated by filtration, washed with petroleum ether, dried overnight in a lyophilizer, sieved, and stored in a freezer. 

A solution to this dilemma is to place soil samples immediately in a freezer located in the field, the temperature of which is continuously monitored, as described previously. Laboratory-prepared storage study samples can then be used to determine test substance stability under freezer storage conditions that match those used in the field and during transportation and final storage. If a valid laboratory storage stability... 

In a plate freezer 2, on a belt in a flow of cold air 3, in trays in cold air 4, partially frozen in a soft-ice machine (continuously scraped cold surface) and finally frozen as in 2. 

To a solution of 1.84 g Na metal in 60 ml ethanol at 5-10° add, over Vi hour with vigorous stirring a mixture of 0.08 M ethyl azidoacetate and 0.02 M 2 (or 2,5 2,3 etc. but not 6) substituted benzaldehyde and continue stirring at 5-10° until nitrogen evolution ceases (about V2-I hour) then stop immediately and rapidly evaporate in vacuum Vi the ethanol (keep temperature below 30°). Basify the solution with solid NH CI, dilute with 500 ml water and extract 3 times with ether. Filter, wash with water to neutrality and dry, evaporate in vacuum the ether (or can dissolve the residue in petroleum ether, or 1 1 petroleum ether.benzene for methoxy compounds, and filter through silica gel) to get the ethyl-alpha-azidocinnamates (1) in about 50% yield. Store in freezer until used in next step. Dissolve 1 g (I) in 100 ml p-xylol and reflux 10 minutes. Evaporate in vacuum (or add 5 ml pentane, filter, evaporate in vacuum) to get about 90% yield of the 4 substituted-2-car-bethoxyindole which can be decarboxylated as described elsewhere here. 

After 30 min, remove the flask from the freezer and, in the fume hood, add 25 mL of ethyl ether. Stopper the flask and, continuing to work in the fume hood, shake vigorously for 30 sec, releasing pressure every 10 sec by removing the stopper. Then add 25 mL of petroleum ether and repeat the shaking and venting procedure for another 30 sec. 

Root powdering and demineralization. Sixty-five frozen and pulp-free tooth roots were ground in a Waring blender and powdered under liquid nitrogen in a freezer mill (Spex, Edison NJ, USA). The sieved powder (< 450 pm) was demineralized in dialysis bags in 0.5 M EDTA, pH 7.4, at 4°C with regular replacement of the solution. Demineralization was continued until no further calcium release could be detected by atomic absorption spectrometry. 

Figure 3.1 Optimum bed depth for fluidized bed freezing production rate per imit bed width for fixed and fluidized beds at an inlet bed temperature of -30°C (solid line = bed length 6 m, broken line=bed length 4m). Reprinted from Reynoso, R.O. and Calvelo, A., Comparison between fixed and fluidized bed continuous pea freezers, Int.. Refrig., 8 (1985) 109-115, with permission from Elsevier.

De Michelis, A. and Calvelo, A., Production rate optimization in continuous fluidized bed freezers, ]. Food Sci., 50 (1985) 669-673. 

Evidence of the stability and recovery of the seeds and banks should be documented. Storage containers should be hermetically sealed, clearly labelled and kept at an appropriate temperature. An inventory should be meticulously kept. Storage temperature should be recorded continuously for freezers and properly monitored for liquid nitrogen. Any deviation from set limits and any corrective action taken should be recorded. 

The sublimation is continued until aU V(CO)e is transferred into the Schlenk receiver. The reaction and collection process requires approximately 1.5 h. The V(CO)g product is transferred in an inert-atmosphere box into a conventional Schlenk tube and stored in a freezer (—30°C or lower) in the dark. Yield 3.25 g... 

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