Concentration and Evaporation

G. R.P.K. Perera, CoT, Kandy

RESOURCE PLANNING FOR FOOD

PROCESSING-1Concentration and EvaporationBy: G. R.P.K.Perera, CoT, Kandy


Concentration What is meant by term Concentration?

Removal of water by means of evaporation or membrane filtration in liquid or semi solid foods with minimal alterations to gain higher solid content.

Examples:Sweetened condensed milkFruit and vegetable juices and nectarsSugar syrupsFlavored syrupsJams, Jelly, SourcePastes (Tomato)


Relationship between Concentration and EvaporationThe activity what we do is evaporation(or membrane filtration) and then the result is concentration of the food/liquid.(The effect of the evaporation is concentration of the food/liquid.)Evaporation is removal of water from a liquid using heat to get concentrated

M. Filtration

EvaporationConcentration


A definition for the EvaporationRemoval of water by vaporizing water in liquid or semi solid foods to gain higher solid content.

Purposes:-Extend the shelf life (Preservation)-Reduce weight and volume (Economical advantages). Reduce transport cost. Reduce handling cost. Reduce storage cost and space


How do Preservation by Concentration?

Movement of matter from high [ ] to low [ ]. So; water comes out from microbe to external

while some solute transfer into microbe. This process disturb the microbial metabolic

activities and prevent their growth due to dehydration and solute imbalance.

[solute][H2O] [H2O]

[Solute]Microbe cell


Basic factors that affect to rate of evaporation-Rate at which heat can be transferred to the liquid-Quantity of heat required to evaporate each kg of water-Maximum allowable T of the liquid-Pressure at which the evaporation takes place-Changes that may occur in foodstuff during evaporation


Methods/Equipments for Concentration

1. Solar Concentratione.g. Salt separation from solar heat.Advantages:

-No power/fuel required-Low pollution

Disadvantages:-High time required-Not suitable for most food-Can’t control


2. Open KettleUse single/double jacketed vat and gas/wood/steam as heating agent.e.g. Jam, Cordial, Nectar Fruit and vegetable syrups sources and pastesAdvantages: -Easy to operate/simple technique -Produce colors and flavors desirable to some productsDisadvantages: -High TO and high time damage the foods’ nutrition value -Thickening on walls reduces the heat transferring rate


3. Flash evaporatorUse clean steam superheated to

above 150oC for direct contact with subdivided food material.

Use for essence recovery equipment on the basis of different boiling point between essence and water to separate volatile flavor constituents.


Flash Evaporator


4. Thin film evaporatorFood is pumped to a vertical cylinder with rotating element which spread the food as thin layer on the cylinder wall.Cylinder is double jacketed construction heated by steam.Low TO and time within the cylinder reduces the heat losses.(an advantage)

G. R.P.K. Perera, CoT, KandyThin Film Evaporator


Pilot scale thin film evaporator


5. Vacuum evaporatorUse low TO vacuum evaporator series.Use for heat sensitive foodse.g. Instant coffee Milk powderAdvantages: -Heat sensitive foods can be evaporated. -Can gain high solute concentration. (effective) -High production rate. (efficient)Disadvantages: -High capital cost.

NB: When concentrating in lower TO with vacuum may not destroy microbes sufficiently. So, use of additional preservation treatment is required.

G. R.P.K. Perera, CoT, KandyVacuum Evaporator


6. Freeze concentrationThe components of the solution is frozen at once.So, the solution is freeze to make tiny crystals of water.Unfrozen concentrated solution portion is separated from the whole.The whole is centrifuged to separate ice crystals and concentrated solution is passed through fine mash while crystals retain on the mash.Repeat this process to get concentrated solution for several times.


7. Ultra filtration and Reverse osmosis(here do not use evaporation technique)Use ultra filtration membrane which is less tighter and a reverse osmosis membrane which is tighter than latter.These are perm selective membranes.The membranes can be synthetic membranes those made of cellulose acetate or polyamide etc.Use for;- Fruit juices Coffee Tea Egg white Soy protein Enzymes Whey separationAdvantages: -Low nutrition loss -Low pollution of waterDisadvantages: -Non valuable constituents also concentrated


Changes during concentration- Change in color and flavor due to carramalization. It is good in caramal production/candy (made of sugar and milk).-Formation of gritty, sugary jelly or jam. This is ocoured in over concentration due to sugar cristerlization.e.g. Sandiness in milk products-Denaturation of protein results gellation during storage.e.g. Condenced milk-Concentration in higher TO may destroy most of nutrients.


Thank You.

Concentration and Evaporation

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