Essentials of Thermal Processing

Gary Tucker, Campden BRI in the United Kingdom. Susan Featherstone is a Director at Safe Food Consulting in South Africa.

Preface

Glossary of Terms

1 History of Thermal Processing

1.1 A brief history of the science and technology of thermal processing

1.2 Food Microbiology as a Science

1.3 Packaging for Heat Preserved Foods

1.3.1 Convenience – the can opener is invented

1.3.2 Other forms of packing for “canned foods”

1.4 Developments in Cannery Equipment

1.5 Food Safety

2 Microbiology of Heat Preserved Foods

2.1 Food microbiology

2.1.1 Fungi

2.1.1.1 Moulds

2.1.1.2 Yeasts

2.1.2 Bacteria

2.1.2.1 Growth and reproduction of bacteria

2.2 Factors that affect the growth of microorganisms

2.2.1 pH

2.2.2 Moisture

2.2.3 Nutrients

2.2.4 Oxidation–reduction potential

2.2.5 Antimicrobial resistance

2.2.6 Biological structures

2.2.7 Relative humidity

2.2.8 Oxygen content/concentration of gases in the environment

2.2.9 Temperature

2.3 Description of some microorganisms of importance to thermal processing

2.3.1 Moulds

2.3.2 Yeasts

2.3.3 Bacteria

2.2.3.1 Thermophiles

2.3.3.2 Mesophiles – spore-forming bacteria

2.3.3.3 Mesophiles – non-spore forming pathogenic and spoilage bacteria

2.3.3.4 Psychrophiles

2.4 Risk of leaker spoilage from damaged or compromised packaging

2.5 A guideline for identifying spoilage in canned foods

3 Hurdles to Microbial Growth

3.1 Control of the microorganism loading

3.2 Use of restrictive pH levels

3.3 Anaerobic environment or modified atmosphere environment

3.4 Low temperatures

3.5 Dehydration or low water activity

3.6 Chemical preservation

3.6.1 Organic acids

3.6.2 Sulphites and nitrites

3.6.3 Antibiotics

3.6.4 Antioxidants

3.7 Irradiation

3.8 Combination Treatments

4 Low Acid Canned Foods

4.1 Production of a thermally processed food

4.2 F03 sterilisation processes

4.3 Commercial sterilisation

4.4 Microorganism death kinetics

4.5 Log reductions

5 Acid and Other Pasteurized Products

5.1 Background

5.1.1 Naturally acid foods

5.2 Pasteurisation

5.2.1 Considerations when designing a safe pasteurisation process

5.2.2 Calculation of pasteurisation values

5.3 Inhibitory factors to microorganism growth

5.4 P-value guidelines

5.4.1 High acid: pH < 3.5

5.4.2 Acid: pH 3.5–4.0

5.4.3 Acid: pH 4.0-4.2

5.4.4 Medium acid: pH 4.2–4.6

5.5 Guidelines and General Recommendations

5.5.1 Guidelines to critical factors in thermal processing of acid foods

5.6 Thermal processing of fruit

 5.3.1 Packaging selection

5.3.2 Oxidation reactions inside an internally plain can of acid fruit

5.3.3 Pigments that discolour in internally plain cans

5.7 Thermal processing of products with low water activity

5.7.1 Jam and high sugar preserves

5.7.2 Canned cake and sponge pudding

5.8 Thermal processing of cured meats

6 Acidified Foods

6.1 Background

6.2 Acidity measurement using pH

6.2.1 The history of pH

6.2.2 The chemistry of pH

6.2.3 Measurement of pH

6.2.3.1 Potentiometric method

6.2.3.2 Colorimetric measurement

6.2.4 Equilibrium pH

6.3 Acidification of foods

6.4 Processing acidified foods

6.5 Design of pasteurisation processes

6.5.1 Medium acid range: pH 4.2–4.6

6.5.2 Acid range: pH 3.5–4.2

6.5.3 High acid range: pH below 3.5

6.6 Hot fill and hold processing

6.7 Critical control points in the production of acidified foods

6.7.1 Ingredients

6.7.2 Heat processing

6.7.3 Post process equilibrated pH

6.7.4 Container integrity

6.7.5 pH during product shelf-life

7 Heat Preserved Chilled Foods

7.1 Understanding microorganism behaviour

7.1.1 Pathogenic microorganisms relevant to chilled foods

7.1.1.1 Clostridium botulinum

7.1.1.2 Bacillus cereus

7.1.2 Microorganisms likely to be found in chilled foods

7.2 Methods of manufacture

7.2.1 Thermal process step applied prior to packaging

7.2.1.1 Low care–high care factories

7.2.2 Thermal process step applied after packaging

7.2.2.1 Caution with latent heat for frozen protein

8 Processing Systems

8.1 In-pack processing: Retort systems

8.1.1 Condensing steam retorts

8.1.2 Crateless retorts

8.1.3 Water immersion retorts

8.1.4 Water spray and cascade

8.1.5 Steam / air retorts

8.1.6 Shaka retorts

8.1.7 Reel & spiral retorts

8.1.8 Hydrostatic retorts

8.2 In-line processing: Heat exchangers

8.2.1 Flow behaviour

8.2.2 Choice of heat exchanger

8.2.3 Maximising product recovery

7.3 New thermal technologies

9 Cook Values and Optimisation of Thermal Processes

9.1 Mathematical analysis of cooking

9.1.1 Cooking equations and kinetic data

9.1.2 Competition between sterilisation and cooking

9.1.3 Optimisation of temperature / time in processing

9.2 Setting process targets

9.2.1 How to select processing conditions without excess quality damage

10 Process Validation: Temperature and Heat Distribution

10.1 Temperature Distribution

10.1.1 Temperature measurement systems

10.2 Heat Distribution

10.2.1 Modes of heat transfer

10.2.1.1 Radiation

10.2.1.2 Conduction

10.2.1.3 Convection

10.2.1.4 Broken heating or mixed heating

10.3 Heat distribution testing

10.3.1 Conducting a HD test

11 Process Validation: Heat Penetration and Process Calculations

11.1 Setting the target process value

11.2 Selecting the conditions for the HP study

11.3 Locating the product cold point

11.4 Process establishment methods

11.4.1 Log reduction methods for HP testing

11.4.1.1 Microbiological spore methods

11.4.1.2 Biochemical systems

11.5 Process calculation methods

11.5.1 General method

11.5.2 Ball method

11.5.3 Numerical methods

11.5.3 Continuous flow with particulates

12 Cooling and Water Treatment

12.1 Chlorine

12.1.1 Chlorine demand and residual chlorine

12.1.2 Using chlorine

12.2 Chlorine dioxide

12.3 Bromine

12.4 Ozone

12.5 Ultraviolet light

12.6 Membrane filtration

13 Handling Processing Deviations

13.1 What constitutes a process deviation

13.2 What can go wrong

13.3 Actions required

13.3.1 TPA actions

13.3.2 Process deviation analysis for broken heating products

13.3.2 Reprocessing

14 Packaging Options for Heat Preserved Foods

14.1 Metal containers

14.1.1 Tin plate

14.1.2 Tin free steel (TFS or ECCS)

14.1.3 Aluminium

14.1.4 Protective coatings (lacquers)

14.1.4.1 Vinyl lacquers 4

14.1.4.2 Organosol lacquers

14.1.4.3 Epoxy-phenolic lacquer

14.1.4.4 Polyester lacquer

14.1.4.5 Acrylic Lacquers

14.1.4.6 Side stripe lacquers to cover the weld

14.1.5 Internally plain (unlacquered) cans

14.1.6 External covering

14.2 Can construction and handling

14.2.1 Product specification

14.2.2 Storage and handling of empty unused cans and ends

14.2.3 Cleaning of empty unused cans

14.2.4 Double seam formation and inspection procedures

14.2.5 Washing of filled cans

14.2.6 Processing of cans

14.2.7 Cooling of cans

14.2.7.1 Corrosion prevention

14.2.8 Secondary packaging

14.3 Glass

1.3.1 Glass manufacture

14.3.2 Closures for sealing glass food containers

14.3.3 Sealing mechanisms

14.3.4 Inspection procedures

14.3.5 Packing and processing

14.3.5.1 Inspection and preparation of containers

14.3.5.2 Filling

14.3.5.3 Capping

14.3.5.4 Atmospheric processing

14.3.5.5 Pressure processing

14.3.5.6 Cooling

14.4 Plastics, flexibles and laminates

14.4.1 Advantages of retortable plastics

14.4.2 Disadvantages of retortable plastics

14.4.3 Polymers used for retortable packaging

14.4.3.1 Polypropylene (PP)

14.4.3.2 Polyethylene terephthalate (PET)

14.4.3.3 Ethylvinylalcohol (EVOH)

14.4.3.4 Polyvinylidene chloride (PVDC)

14.4.3.5 Polyamide (PA)

14.4.3.6 Aluminium

14.4.3.7 Glass-coated barrier films

14.4.4 Types of packages used for thermally processed foods

14.4.4.1 Retort pouches

14.4.4.2 Plastic cans and pots

14.4.4.3 Retortable composite carton

14.4.5 Processing considerations – control of headspace

15 Incubation Testing

15.1 Purpose of incubation tests

15.2 Causes of spoilage

15.2.1 Leaker spoilage

15.2.2 Under-processing

15.2.3 Thermophilic spoilage

15.3 Descriptive terms for canned food spoilage

15.4 Methods for incubation testing

15.4.1 Sample size

15.4.2 Temperatures and times for incubation

15.4.2.1 Thermophilic organisms

15.4.2.2 Mesophilic organisms

15.4.3 Post incubation inspection of containers

15.5 Biotesting

16 Critical Factors in Thermal Processing

16.1 Background

16.2 Key aspects of hygiene control systems for food processing (from Codex Alimentarius)

16.3 Identifying critical control points in thermal processing

16.3.1 Microbial load or bio-burden

16.3.2 pH of the product

16.3.3 Water activity (aw)

16.3.4 Consistency

16.3.5 Presence, concentration and types of preservatives

16.3.6 Rehydration

16.3.7 Blanching

16.3.8 Size and style of in-going ingredients

16.3.9 Container, packing and filling considerations

16.3.9.1 Headspace

16.3.9.2 Container vacuum and exhausting of containers

16.3.9.3 Container size and geometry

16.3.9.4 Initial temperature of product

16.3.10 Process related critical factors

16.3.10.1 Processing method

16.3.10.2 Processing medium

16.3.10.3 Type and characteristics of heat processing system

16.3.10.4 Processing temperature

16.3.10.5 Processing time

16.3.10.6 Processing at high altitudes

17 Environmental Aspects of Thermal Processing

17.1 Lifecycle Assessment (LCA)

17.1.1 Impact categories

17.1.1.1 Global warming potential (GWP)

17.1.1.2 Pesticide use / ecotoxicity

17.1.1.3 Abiotic resource use

17.1.1.4 Acidification potential

17.1.1.5 Eutrophication potential

17.1.1.6 Land use

17.1.1.7 Water use

17.2 Greenhouse gas emissions

17.2.1 Case study: Bottled apple juice

17.2.1.1 Raw materials (0.407 kg CO2e/PU)

17.2.1.2 Manufacture (0.061 kg CO2e/PU)

17.2.1.3 Transportation (0.057 kg CO2e/PU)

17.2.1.4 Waste (0 kg CO2e/PU)

17.2.1.5 Overall carbon footprint (0.525 kg CO2e/PU)

17.2.1.6 GHG emissions for other food products

Index