Introduction to food processing; drying ‐ Fundamentals
Classification‐general ideas
Why so many dryer types?
Key criteria for classification
Criteria for dryer selection
Different dryer types
Energy related issues in drying
Special/Innovative dryers
Closure
Food Processing
• Need of food processing ‐ to avoid the spoilage of foods due to various reasons; to increase shelf life; to make food products available through out the year
• The spoilage could be due to physical damage, chemical damage, microbial attack
• Various food processing methods – Freezing, canning, preserving in syrup, food irradiation, salting, vacuum packaging, dehydration
• canning and freezing – best way to retain the taste, appearance, and nutritive value of fresh food (Cost involvement)
• Drying/Dehydration – very much cost‐effective; product takes much less storage space than canned or frozen foods; Some dehydrated products have very good rehydration properties
Drying Fundamentals
Removal of a liquid from a solid/semisolid/liquid to produce solid product by thermal energy input causing phase change (Sometimes converts solid moisture into vapor by sublimation eg. Freeze drying with application of heat.)
Needed for the purposes of preservation and storage, reduction in cost of transportation, etc.
Most common and diverse operation with over 100 types of dryers in industrial use
Competes with distillation as the most energyintensive
operation
Removes moisture from food so bacteria, yeasts & molds can’t grow and spoil food
Slows down action of enzymes but doesn’t inactivate them
Temperatures for Drying
Optimum temperature for drying food is 140°F
If higher temps are used, food cooks instead of drying
Avoid “case hardening” – dried outside and moisture is trapped inside – mold results
Helps Drying…
Low humidity aids drying
Increasing air current speeds up drying, removes air around food
Ways To Dry Food
Foods can be dried in the sun, but often doesn’t work well in Illinois…need several days of high temp and low humidity
Dry in an oven
Dry in food dehydrator
Drying Out-Of-Doors
Sun Drying
Dry fruits, high sugar & acid make them safe
Don’t dry vegetables or jerky/meat outdoors
Need hot, dry, breezy days
Temp of 85ºF. or higher, for several days with humidity below 60%
Need to cover, watch materials used and control for insects and pests
Out-Of-Doors
Solar Drying
Need to make a dryer
Need to stir and turn food several times a day
Need several days…
Vine Drying
Dry beans, lentils and soybeans
Leave bean pods on vine until beans inside rattle
If not dried can dry further in oven or dehydrator
Pasteurization
Freezer Method – seal food in freezer plastic bags. Freeze at 0ºF for at least 48 hours
Oven Method – Place food in single layer on fray or in
shallow pan. Place in oven preheated to 160ºF for 30 minutes
Drying Foods Indoors
Food dehydrators
Counter-top
Convection ovens
Conventional ovens
Food Dehydrators
Small electrical appliance for drying foods indoors
Electric element for heat & fat and vents for air circulation
Dry foods fast at 140ºF
Buy at department stores, mail-order, garden supply, internet
Costs?
Costs vary depending on features. Some are expandable & extra trays can be purchased. Twelve square feet of drying space dries about a half-bushel of produce.
Major disadvantage of dehydrator is limited capacity.
Foodelphi.com Science of Food Engineering