FLUID FOOD PROCESSING
Fluid foods are those products which have flow properties and can be pumped. They may be secretions, extracts or formulated in a fluid from selected food ingredients. They may be perishable or shelf stable.
Unit operations common to almost all fluid foods are:
-fluid flow
-heat transfer (heating and cooling)
-mixing
In addition, the following unit operations also apply to certain fluid food products: -mechanical separation (such as for the production of cream from milk) -mass transfer (such as distillation for production of some liqueurs; air incorporation into a milkshake; removal of water in the production of evaporated milk) -size reduction (such as emulsion preparation in salad dressing)
Perishable products with a shelf life of less than 30 days and generally sold and kept as refrigerated products include:
milk
half-and-half
coffee cream
whipping cream
cream
yogurt
sour cream
liquid coffee whitener
whipped topping
fruit juices
some salad dressings
These products are maintained under refrigeration to extend their shelf life with minimal change in flavor, color and texture. Their shelf life varies from about 7-21 days. Most of these products have components that are sensitive to high heat processes, and lose quality if retorted.
Shelf stable products with a shelf life in excess of 6 months and stored and sold at room temperature include:
carbonated beverages
soups
sauces
most salad dressings
canned juices
In these products, the ability to provide a long shelf life and convenience of use outweighs the changes in color, flavor and texture caused by processing. Soups and sauces depend upon high heat treatment to eliminate pathogenic spore forming organisms.
The following table shows the unit processes involved in the processing of a number of fluid food products:
Some selected examples of fluid product processing operations:
Fruit and vegetable juices:
Unit processes for all juices include:
-extraction of juice by squeezing or pressing, -removal of solids by filtration or centrifugation, -deaearation under vacuum to protect vitamin C, -pasteurization
For frozen products, additional processes include concentration, essence recover and addition and freezing.
For canned products, the juice may or may not be concentrated, placed in a can and retort sterilized.
Pourable salad dressing:
Unit processes involve: -preparation of pre-emulsion by, addition of ingredients, (-oil, -sugar, -water, -gums, -eggs, -spices and -acid (vinegar)
The ingredients are mixed at low speed to incorporated all ingredients into a macro-emulsion -preparation of final dressing is achieved by blending through a colloid mill to make a stable micro-emulsion, which involves: -fluid flow, -size reduction , packaging and storage
Yogurt:
Operations include: -standardization of milk, separation to remove cream, addition of solids, mixing, -heat treatment ( typically at 180oF for 10 minutes), -homogenization, -addition of culture, -incubation to produce acid, -cooling, -blending in fruit puree and mixing, -packaging, and -refrigerated storage
Liquid Coffee whitener (fluid - frozen)
Operations include-mixing of ingredients (oil, protein, emulsifier, gums, phosphates, water, sugar), -pasteurization and homogenization, -cooling, -packaging, -freezing, -maintenance in frozen storage