Commercial Preservation (Leaving Cert Home Economics): Revision Notes
Commercial Preservation
Commercial preservation techniques are vital for extending the shelf life of food products whilst maintaining their safety, quality, and nutritional value. These methods help reduce food waste and ensure food security in the modern food industry.
Commercial freezing methods
Commercial freezing works by lowering food temperatures to levels that slow down enzyme activity and prevent harmful microorganisms from growing. Different freezing techniques are used depending on the type of food and quality requirements.
Food preservation is the process of treating and handling food to prevent or significantly slow down spoilage, quality loss, and nutritional decline.
Blast freezing
This rapid freezing technique uses powerful fans to circulate extremely cold air around food products. The process typically operates at temperatures between -30°C and -40°C.
Key advantages:
- Creates smaller ice crystals, which cause less damage to food structure
- Better preserves texture and flavour compared to slower freezing methods
- Reduces time spent in the danger zone, minimising bacterial growth risk
Common applications: Meat products, seafood, prepared meals, and bakery items.
Plate/contact freezing
This method involves placing food directly between metal plates that have been cooled to sub-zero temperatures. The direct contact ensures efficient heat transfer and uniform freezing.
Key advantages:
- Excellent for flat or uniformly shaped products
- Provides consistent freezing results
- Efficient heat transfer process
Common applications: Fish fillets, meat cuts, and pre-packaged items with uniform thickness.
Cryogenic freezing
The fastest commercial freezing method, using extremely low temperatures achieved through liquid nitrogen or carbon dioxide exposure.
Key advantages:
- Creates very small ice crystals due to ultra-rapid freezing
- Minimal damage to food cell structure
- Excellent for preserving delicate textures
Common applications: High-quality products where texture is crucial, such as gourmet dishes, fruits, and premium seafood.
Fluidised bed freezing
This technique freezes small, individual food pieces whilst they are suspended in circulating cold air through a perforated bed system.
Key advantages:
- Ensures quick and uniform freezing
- Prevents pieces from sticking together
- Ideal for small, particulate foods
Common applications: Vegetables, fruits, and small seafood like prawns.
Heat treatment methods - canning and bottling
Heat treatment processes use high temperatures to destroy harmful microorganisms and extend shelf life. The key principles involve sterilisation, airtight sealing, and controlled heat application.
Sterilisation is the process of using heat to destroy bacteria, yeasts, moulds, and enzymes that could cause food spoilage or illness.
Worked Example: The Canning Process
The complete canning process follows these essential stages:
- Preparation: Food is cleaned, peeled, chopped, or prepared as required
- Filling: Prepared food is placed into cans or jars
- Air removal: Air is evacuated to prevent oxidation and spoilage
- Sealing: Containers are sealed to prevent contamination
- Sterilisation: Sealed containers are heated to destroy harmful organisms
- Labelling: Information about contents, nutrition, and expiry dates is added
Methods of canning
Aseptic canning
Food and containers are sterilised separately, then combined in a sterile environment. This method maintains higher nutritional quality and is commonly used for dairy products, puddings, and fruit juices.
High-acid food canning
Used for foods with pH 4.6 or lower, such as fruits, pickles, and tomatoes. The acidic environment naturally inhibits harmful bacteria like Clostridium botulinum, requiring lower sterilisation temperatures.
Low-acid food canning
Applied to foods with pH above 4.6, including vegetables, meats, and poultry. These foods require higher temperatures for effective sterilisation since they don't naturally inhibit bacterial growth.
The pH level of food is crucial in determining the appropriate canning method. High-acid foods naturally create an environment that inhibits dangerous bacteria, while low-acid foods require more intensive heat treatment to ensure safety.
Suitable foods for canning
- Fruits and vegetables: Benefit from their natural acidity
- Meats and poultry: Require careful processing due to low-acid content
- Seafood: Needs specific techniques due to delicate nature
- Dairy products: Processed using aseptic methods
Commercial dehydration methods
Dehydration preserves food by removing water content, which inhibits microorganism growth and slows enzymatic reactions. This technique maintains nutritional value whilst significantly extending shelf life.
Dehydration is the removal of water from food, leading to a significant reduction in moisture content that prevents spoilage.
Fluidised bed drying
Hot air passes through a bed of particulate food items, causing them to behave like a fluid whilst drying occurs.
Key advantages:
- Rapid and uniform drying process
- Minimal nutrient loss during processing
- Consistent moisture removal across all particles
Common applications: Small-sized products like grains, pulses, and diced vegetables.
Accelerated freeze drying (AFD)
Also known as lyophilisation, this process freezes food first, then reduces surrounding pressure whilst applying heat. This allows frozen water to change directly from solid to gas without becoming liquid.
Key advantages:
- Maintains original shape, size, and colour
- Preserves nutritional content and flavour exceptionally well
- Produces high-quality finished products
Common applications: Premium products like coffee, fruits, and specialty ready-to-eat meals.
Sun drying
One of the oldest preservation methods, using natural sunlight and air movement to remove moisture from food.
Key advantages:
- Cost-effective and environmentally friendly
- Uses renewable solar energy
- Simple process requiring minimal technology
Limitations:
- Weather-dependent and unreliable
- Risk of contamination from dust and insects
- Limited control over drying conditions
- Slower process with inconsistent results
Common applications: Fruits like grapes (raisins), plums (prunes), and tomatoes in suitable climates.
Fermentation
Fermentation uses beneficial microorganisms to preserve food whilst enhancing its nutritional value, taste, and digestibility. This ancient preservation method creates natural preservatives that inhibit harmful bacteria.
Fermentation is a metabolic process where microorganisms convert sugars into acids, gases, or alcohol, preserving food whilst enhancing its properties.
Underlying principles of fermentation
Anaerobic environment: Most fermentation occurs in oxygen-limited conditions where beneficial microorganisms can thrive.
Microbial activity: Specific bacteria, yeasts, or other microorganisms feed on carbohydrates in food, producing alcohol, acids, and gases as by-products.
Natural preservation: The acids or alcohol created during fermentation act as natural preservatives, creating an environment hostile to harmful bacteria.
Types of fermentation
Alcoholic fermentation
Yeasts convert sugars into alcohol and carbon dioxide. This process is fundamental in producing beverages like beer, wine, and spirits.
Lactic acid fermentation
Lactic acid bacteria transform sugars into lactic acid. This method is used for yoghurt, kefir, sauerkraut, and kimchi production.
Acetic acid fermentation
Alcohol is converted into acetic acid, with vinegar production being the primary example.
Each type of fermentation creates different end products and preservative effects, making specific methods suitable for particular foods and desired outcomes.
Examples of fermented foods
- Dairy products: Yoghurt, cheese, and kefir
- Vegetables: Sauerkraut, kimchi, and pickles
- Breads: Sourdough bread (fermentation aids rising process)
- Beverages: Wine, beer, and kombucha
Food irradiation
Irradiation is a modern preservation method that uses ionising radiation to eliminate microorganisms, insects, and parasites from food, extending shelf life and improving safety.
Food irradiation involves exposing food to ionising radiation such as gamma rays, electron beams, or X-rays to destroy harmful organisms.
How irradiation works
The high-energy radiation penetrates food and breaks chemical bonds in harmful organisms' DNA, effectively killing or inactivating them. Importantly, this process doesn't significantly raise food temperature or alter nutritional content.
Radura symbol and regulation
The Radura symbol is an international green radial pattern that must appear on irradiated food packaging. This regulatory requirement ensures consumer awareness and transparency about the use of irradiation technology.
Advantages of irradiation
- Extended shelf life: Slows ripening in fruits and vegetables
- Enhanced food safety: Eliminates harmful bacteria and pathogens
- Pest control: Kills insects and parasites without chemical pesticides
- Cold pasteurisation: Achieves pasteurisation effects without heat
- Reduced chemical preservatives: Decreases reliance on chemical additives
Disadvantages of irradiation
- Public perception concerns: Consumer misconceptions about safety
- Minor nutritional changes: Small losses in some vitamins
- Higher costs: More expensive than traditional preservation methods
- Packaging requirements: Needs specialised materials resistant to radiation
- Limited effectiveness: Some microorganisms show radiation resistance
Effects of preservation on food
Different preservation methods affect food characteristics in various ways, impacting texture, flavour, nutritional content, and overall quality.
Effects of freezing on food
Texture changes: Ice crystal formation can damage cell walls, particularly in fruits and vegetables, sometimes leading to softer textures after thawing.
Nutritional preservation: Generally maintains nutritional value well, though some water-soluble vitamins like Vitamin C may decrease slightly.
Flavour retention: Most foods maintain their flavour effectively, though spices may become more pronounced.
Effects of canning on food
Nutritional changes: Heat-sensitive vitamins (B and C) may be reduced during processing, but minerals and fat-soluble vitamins are well preserved.
Texture modifications: Heat treatment can soften fruits and vegetables as cell walls break down.
Flavour enhancement: Can intensify certain flavours but may also cause changes due to interaction with canning liquids.
Effects of chemical preservation on food
Nutritional impact: Generally minimal direct effect on nutrients, though some preservatives may interact with food components.
Safety considerations: Some preservatives can trigger allergic reactions in sensitive individuals.
Colour and flavour effects: Certain preservatives can alter food appearance and taste - for example, sulphites prevent browning in dried fruits.
Effects of dehydration on food
Nutrient concentration: Generally preserves minerals and fibre well, though some heat-sensitive vitamins may be lost.
Texture changes: Food becomes more leathery or brittle, with concentrated flavours.
Flavour intensification: Natural tastes become more concentrated, often enhancing the food's original characteristics.
Key Points to Remember:
- Blast freezing creates smaller ice crystals, preserving food texture better than slow freezing methods
- High-acid foods (pH 4.6 or below) require lower canning temperatures than low-acid foods
- Fermentation produces natural preservatives whilst enhancing nutritional value
- The Radura symbol must appear on all irradiated food products for consumer awareness
- Different preservation methods have varying effects on food texture, nutrition, and flavour - choose the method based on desired end product quality