Food Drying & Dehydration — Winter 2018

What is equilibrium moisture content? Write its significance also.

Differentiate between direct and indirect dryer. List out the characteristics and properties of various types of dry powders and particulate.

Describe the drying rates periods for agricultural products. Derive equation for constant rate drying.

List out all the unique features of drying.

Discuss Parallel, Series and Krisher models to predict thermal conductivity.

The initial moisture content of a food product is 70% (wet basis), and the critical moisture content is 25% (wet basis). If the constant drying rate is 0.1 kg H O/(m2s), compute the time required for the product to begin the2 falling rate drying period. The product has a cube shape with 5-cm sides, and the initial product density is 900 kg/m3.

Draw the following generalised curve for the agricultural materials:

Drying curve (ii) Drying rate curve (iii) Water activity stability diagram (iv) Moisture content and bed depth for different inlet temperature

Compute the equilibrium moisture content for popcorn at 20°Cand 50% relative humidity. Given that constant c = 6.5 x 10-4 and n=1.8

What is moisture sorption curve? Describe the phenomena of hysteresis.

(i) Define wet and dry basis moisture content and write the expression to convert wet basis to dry basis moisture content. (ii) 500 kg of paddy at 22 % moisture content (wb) is dried to14 % moisture content (wb) for milling. Calculate the amount of moisture removed in drying

Discuss in brief the features of solar drying.

Give a detail classification of dryers used in food industry.

Afood containing 80% water is to be dried at 100°Cdown to moisture content of 10%. If the initial temperature of the food is 21°C, calculate the quantity of heat energy required per unit weight of the original material, for drying under atmospheric pressure. The latent heat of vaporization of water at 100°Cand at standard atmospheric pressure is 2257 kJ kg-1. The specific heat capacity of the food is 3.8 kJ kg-1 °C-1 and of water is 4.186 kJ kg-1 °C-1. Find also the energy requirement/kg water removed.

Discuss the advantage of osmotic dehydration.

What are the major chemical changes that take place during drying of food materials?

Acabinet dryer is being used to dry a food product from 70 % moisture content (w.b.) to 6% moisture content (w.b.). The drying air enters the system at 54 0C and 10% RH and leaves at 30 0C and 70% RH. The product temperature is 25 0C throughout. Calculate the quantity of air required for drying on the basis of 1 kg of product solid. Given absolute humidity of air at 30 0C & 70% RH=0.0186 kg H O/kg dry air2 54 0C & 10% RH=0.0094 kg H O/kg dry air2

Define thin layer and deep bed drying.

Describe the physical properties of dried foods.

Write short notes on:

Water activity (ii) Rehydration ratio (iii) Shrinkage during drying (iv) Heat utilization factor

What are features of fluidized bed dryer?

Describe the principle for selection of dryer in food industry.

Explain the construction, working and application of following:

Freeze Dryer (ii) Spray Dryer

Explain the concept of hybrid drying.

What is heat pump dryer? Explain its working.

Describe the construction and features of super heated steam drying?2