Slush drying

Fresh fruit juices are complex aqueous slurries (80% to 90% by weight of water) containing numerous organic compounds. Most juices are very heat-sensitive because of the potential for enzymatic reactions and the volatilization 

As reported by Chandrasekaran and King (1971), the slush drying of apple juice takes place at a nearly constant drying rate with respect to time and solids content, especially if an allowance is made for the lower amount of water contained in a given volume of juice at higher solids concentrations. 

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To handle dehydration of fruit juices, a technology called slush drying was proposed and tested with apple juice for the potential loss of volatile flavor and aroma substances (Chandrasekaran and King 1971 Lowe and King, 1974). The principle of this method stems from the dependence of the freezing point on the concentration of dissolved solids (Figure 20.1). It boils down to the fact that drying takes place from an ice-liquid mixture (slush) in which 20% to 70% of the water present in the fruit juice is frozen (the... 

Essentially, slush drying is a batch process, which starts with cooling the liquid to be concentrated to a temperature intermediate between the freezing point and the eutectic point of the slurry (see Figure 20.1). The semisolid material is then placed in a vacuum chamber and air is evacuated to reduce the pressure to around 1 mm Hg. The ice crystals are sublimated by heat supplied by an internal heater. The water vapor and volatile compounds are sucked away by a vacuum pump and condensed in a vapor trap (Figure 20.3). 

Figure 20.4 History of the surface temperature for slush drying and freeze-drying...

C bol the solution of re-butyl-hthium to — 35° in a Dry Ice - acetone bath and add, whilst stirring vigorously, a solution of 48 g. of ni-chlorobromo-benzene (Section IV,62) in 75 ml. of anhydrous ether. Stir for 8-10 minutes and pour the mixture with stirring on to a large excess of sohd carbon dioxide in the form of a Dry Ice - ether slush contained in a -htre beaker. Isolate the acid as detailed above for p-Toluic acid and recrystal-lise it from hot water. The yield of ni-chlorobenzoic acid, m.p. 150-151°, is 27 g. 

The table below gives the lowest temperature that can be obtained from a mixture of the inorganic salt with finely shaved dry ice. With the organic substances, dry ice (—78°C) in small lumps can be added to the solvent until a slight excess of dry ice remains or liquid nitrogen (—196°C) can be poured into the solvent until a slush is formed that consists of the solid-liquid mixture at its melting point. 

Seafood. Sorbates are used to extend the shelf life of many seafood products, both fresh and processed (103,104). For smoked or dried fish, an instantaneous dip in 5 wt % potassium sorbate or a 10-minute dip in 1.0 wt % potassium sorbate prior to drying or smoking inhibits the development of yeast and mold (105,106). For fresh fish, sorbates can be incorporated at approximately 0.5 wt % into the ice, refrigerated seawater, or ice-water slush in... 

After leaving the reactant zone, the product stream entered a 0.5 in diameter PTFE tube cooled either by salt-ice bath or acetone-carbon dioxide slush bath [15,16]. The gas mixture was scrubbed in a soda-lime tower. Hydrogen fluoride was trapped by adding sodium fluoride to the reaction mixture or simply adding water. Then, the product solution was extracted with dichloromethane, washed with aqueous NaHCOj solution and dried over MgS04. Thereafter, the solvent was evaporated, leaving the crude product. 

Into a size 6A porcelain boat (88 X 13 X 10 mm.) is placed 10.0 g. (0.0113 mol) of Ag2ReBr6 (as much as 15 g. may be processed readily), and the boat is positioned near the sealed end of a 25 X 300 mm. Pyrex tube fitted with an inner 29/44 S.T. sleeve joint. The tube is connected to a mechanical vacuum pump (capable of reducing the pressure to ca. 50 p) via either a trap cooled by liquid nitrogen or a trap cooled by a Dry Ice-isopropyl alcohol slush, which is in turn connected to an 11-mm. Vycor combustion tube packed with copper gauze and maintained at 600° by means of a furnace. (Either protective system between the tube and the pump will serve to remove bromine, one of the reaction products.)... 

The propyne is passed directly from the tank or lecture bottle to a cold-finger condenser filled with a slush of Isopropyl alcohol and dry ice. The condenser is attached to a 20n-mL, three-necked flask equipped with a gas-inlet adapter and a glass stopper. The flask has been previously calibrated to hold 85 mL of liquid. 

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