6. Heating and cooling liquid and solid food

Batch heating in industry

How fast heating takes place formula

Types of heat exchangers: plate system

Types of heat exchangers: tubular system

Types of heat exchangers: tube in shell

Types of heat exchangers: scraped surface

Flow directions

Options for heating of semi-solid food

Options:

1. First package, then heat

2. First heat than use aseptic packaging

Process for first packaging and then heating

• Batch system: autoclave

• Solid products (cans/bottles): autoclave

• Steam injection

• High pressure at sterilization temperature

• Cooling by spraying water

• Residence time

Process for first heating and then packaging

• Steam injection (direct heating)

• continuous system + aseptic packaging

• Semi solid foods

Biot number

• A number to help you find out if resistance is inside limiting or outisde limiting

• Bi>10 → resistance inside limiting

• Bi<0.1 → resistance outside limiting

Meaning of high and low Bi

• Bi large → h_ext high and/or gamma low and/or d_c large → high delta T

• Bi small → h_ext low and/or gamma high and/or d_c small → low delta T

Dimensionless temperature Y

Y is always between 0 and 1