Podcast
Questions and Answers
What is the primary purpose of chilling food?
What is the primary purpose of chilling food?
Which of the following temperature ranges is suitable for storage of pasteurized canned meat?
Which of the following temperature ranges is suitable for storage of pasteurized canned meat?
How does chilling affect the respiration of fresh foods?
How does chilling affect the respiration of fresh foods?
Which factor does NOT influence the shelf life of fresh crops in chill storage?
Which factor does NOT influence the shelf life of fresh crops in chill storage?
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Which product would generally be stored at temperatures from 0ºC to +8ºC?
Which product would generally be stored at temperatures from 0ºC to +8ºC?
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What effect does mechanical damage at harvest have on the shelf life of crops?
What effect does mechanical damage at harvest have on the shelf life of crops?
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Which chilling storage temperature is recommended for fresh fish and meats?
Which chilling storage temperature is recommended for fresh fish and meats?
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Combining chilling with which storage condition enhances its preservative effect?
Combining chilling with which storage condition enhances its preservative effect?
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Which type of micro-organism has an optimum growth temperature of 55–65ºC?
Which type of micro-organism has an optimum growth temperature of 55–65ºC?
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What is the primary microbiological concern with chilled foods stored below 5ºC?
What is the primary microbiological concern with chilled foods stored below 5ºC?
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Which class of food includes raw or uncooked ingredients?
Which class of food includes raw or uncooked ingredients?
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How long should cooling occur for cooked–chilled foods after cooking?
How long should cooling occur for cooked–chilled foods after cooking?
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Which equipment component is responsible for absorbing latent heat in a mechanical refrigerator?
Which equipment component is responsible for absorbing latent heat in a mechanical refrigerator?
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What is a primary property required of refrigerants used in mechanical refrigeration?
What is a primary property required of refrigerants used in mechanical refrigeration?
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Which cryogen is commonly used in cryogenic chilling?
Which cryogen is commonly used in cryogenic chilling?
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What is an important factor in maintaining the quality of chilled foods during storage?
What is an important factor in maintaining the quality of chilled foods during storage?
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What encapsulates the conditions necessary for the shelf life of chilled processed foods?
What encapsulates the conditions necessary for the shelf life of chilled processed foods?
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What happens during the partial vacuum formation of the cook–pasteurise–chill system?
What happens during the partial vacuum formation of the cook–pasteurise–chill system?
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Which of the following refrigerants is noted for being low-cost and commonly used?
Which of the following refrigerants is noted for being low-cost and commonly used?
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What aspect is critical for managing the safety of chilled foods in storage?
What aspect is critical for managing the safety of chilled foods in storage?
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What is one of the key hazards associated with cryogenic gases?
What is one of the key hazards associated with cryogenic gases?
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How long can cooked, packaged products in Class 4 generally last?
How long can cooked, packaged products in Class 4 generally last?
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Study Notes
Chilling Unit Operation
- Chilling is a unit operation used to reduce food temperature to between 1ºC and 8ºC.
- This reduces biochemical and microbiological changes, extending shelf life for fresh and processed foods.
- Chilling minimally alters sensory characteristics and nutritional properties, perceived by consumers as convenient, high-quality, and healthy.
- Often used with other operations (like fermentation or pasteurization) to improve mildly processed food shelf life.
- Combining chilling with controlled storage atmosphere is more effective than either method alone.
Categories of Chilled Foods
- Category 1: -1ºC to +1ºC (fresh fish, meats, sausages, ground meats, smoked meats, breaded fish).
- Category 2: 0ºC to +5ºC (pasteurized canned meat, milk, cream, yogurt, prepared salads, sandwiches, baked goods, fresh pasta, soups, sauces, pizzas, pastries, unbaked dough).
- Category 3: 0ºC to +8ºC (fully cooked meats/fish pies, cooked/uncooked cured meats, butter, margarine, hard cheese, cooked rice, fruit juices, soft fruits).
Fresh Foods and Chilling
- Biochemical changes increase logarithmically with temperature.
- Chilling reduces enzymatic and microbiological changes, slowing fresh food respiration.
- Shelf life factors include food type, crop part, harvest condition (damage, contamination, maturity), temperature of harvest/storage/distribution/retail, and storage atmosphere humidity.
Processed Foods and Chilling
- Microorganisms are categorized by temperature range: thermophilic, mesophilic, psychrotrophic, psychrophilic.
- Chilling prevents thermophilic and many mesophilic microorganism growth.
- Key microbiological concern in chilled foods: pathogens growing at low temperatures or with temperature fluctuations (food poisoning).
- Examples of chilling-surviving pathogens: Aeromonas hydrophilia, Listeria spp, Yersinia enterocolitica, some Bacillus cereus strains, and enteropathogenic Escherichia coli.
Chilled Processed Foods - Shelf Life Factors
- Food type, prior process to microbe and enzyme inactivation, hygiene control, packaging barrier properties.
- Temperatures during processing, distribution, storage influence shelf life significantly.
- Chilled foods are categorized into risk classes:
- Class 1: Raw/uncooked ingredients (salads, cheeses, raw meat/fish)
- Class 2: mixture of cooked and low-risk raw ingredients
- Class 3: Cooked and packaged products
- Class 4: Cooked after packaging (REPFEDs) with >40 day shelf life
Cook-Chill Food Preparation and Storage
- Portion and chill cooked foods within 30 minutes of cooking.
- Complete chilling to 3ºC within 90 minutes and store at 0–3ºC.
- Cook-pasteurize-chill process: fills food into flexible containers, removes oxygen, and seals.
- Pasteurizes at 80ºC for 10 minutes, followed by rapid cooling to 3ºC, for a 2-3 week shelf life.
Chilling Equipment - Mechanical Refrigerators
- Mechanical refrigerators: evaporator, compressor, condenser, expansion valve.
- Evaporation of refrigerant absorbs latent heat, cooling the environment.
- Cycle: refrigerant vapor to compressor (pressure increase), to condenser (vapor condenses), to expansion valve (pressure decrease for reuse).
Refrigerants and Cryogenic Chilling
- Refrigerants: Freon-22, ammonia, propane (potential).
- Cryogenic: uses solid/liquid carbon dioxide or liquid nitrogen as refrigerants.
- Carbon dioxide limitations: asphyxiation risk (0.5% max), additional safety precautions.
Chill Storage Principles
- Maintain temperature with refrigerated air circulation (fans).
- Foods are stacked to allow air circulation (important for heat removal and flavor development).
- Humidity control is critical for fresh produce.
Temperature Monitoring
- Temperature monitoring is crucial for product safety and quality management throughout the entire production/distribution chain.
- Recent technological advancements allow large data storage and computer integration.
Effects of Chilling on Foods
- Chilling effects: food hardening due to fat/oil solidification; enzymic browning, lipolysis, color/flavor deterioration; starch retrogradation (staling).
- Lipid oxidation is a major quality loss in cook-chilled products (warmed-over flavor in cooked meats).
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Description
This quiz explores the chilling unit operation in food preservation, focusing on its temperature control and effects on microbial and biochemical changes. It also covers various categories of chilled foods and their respective temperature ranges, highlighting the importance of chilling for extending shelf life and maintaining quality.
