Food Spoilage & Food Safety

Conditions Affecting Microbial Growth (FATTOM)

Every micro-organism needs a specific environment to feed, grow, and multiply. In food science, we summarise these factors using the acronym FATTOM:

• Food: Most bacteria prefer moist, protein-rich foods such as meat, fish, milk, and eggs. We call these high-risk foods. Moulds and yeasts prefer carbohydrate foods containing sugars or starch, such as bread, fruit, and jam.
• Acidity (pH): Bacteria generally grow best in a neutral or slightly alkaline environment between pH 6.5 and 7.5. Most bacteria, including food poisoning bacteria, cannot multiply below pH 4.5, which is why pickling works. Moulds and yeasts tolerate acid far better. Moulds survive across a wide pH range of 2.0 to 8.0, while yeasts prefer mildly acidic conditions between pH 4.0 and 6.0.
• Temperature: Micro-organisms fall into three distinct temperature categories based on their optimum growth points:
• Psychrophiles: Thrive in the cold from -5°C to 20°C.
• Mesophiles: Prefer moderate warmth from 20°C to 45°C, with 37°C being the optimum for human pathogens.
• Thermophiles: Thrive in high heat from 45°C to 75°C.
• The temperature band between 5°C and 63°C is called the danger zone, where food poisoning bacteria multiply rapidly. Domestic refrigerators must stay between 0°C and 5°C to slow growth, and cooking food to a core temperature of 75°C kills living vegetative bacteria.
• Time: Under ideal conditions, a single bacterium divides into two every 20 minutes by binary fission. Within a few hours, a tiny bacterial load can escalate into millions of cells.
• Oxygen: Organisms have different oxygen requirements. Aerobes must have oxygen (most moulds), anaerobes grow only in the absence of oxygen (Clostridium botulinum in sealed cans), and facultative anaerobes can adapt to grow with or without it (Salmonella, Staphylococcus aureus, and yeasts).
• Moisture: Microbial cells need available, unbound water to transport nutrients. This is measured as water activity ($a_w$), where pure water equals 1.0. Bacteria require high moisture with $a_w \ge 0.90$, yeasts need $a_w \ge 0.85$, and moulds can tolerate drier conditions down to $a_w \approx 0.70$.

Bacteria: Structure, Reproduction, and Endospores

Bacteria are single-celled microscopic organisms. A typical bacterial cell contains internal cytoplasm, ribosomes for protein synthesis, and a single circular loop of bacterial DNA lying free in the cell without a nuclear membrane. Surrounding the cell is a delicate cell membrane and a rigid protective cell wall. Some strains have a slimy outer capsule that defends them against drying out and white blood cells, and some possess flagella, which are whip-like tails used for swimming through liquids.

We classify bacteria by shape into three groups. Spherical cells are called cocci (occurring in chains such as Streptococcus or clusters like Staphylococcus), rod-shaped cells are bacilli (such as Salmonella and Listeria), and spiral forms are called spirilla (such as Campylobacter). They are also classified using Gram staining. Gram-positive bacteria possess a thick peptidoglycan cell wall that retains crystal violet dye, turning them purple under a microscope. Gram-negative bacteria have a thinner wall covered by an outer membrane; they lose the purple dye during washing and take up the pink safranin counterstain instead.

Bacteria multiply asexually by binary fission. The circular DNA replicates, the cell elongates to pull the two copies apart, a cross-wall develops down the centre, and the cell cleaves into two identical daughter cells. In a closed environment, a bacterial population passes through four distinct phases: the lag phase (adapting to conditions without dividing), the log phase (rapid, exponential division), the stationary phase (death rate matches birth rate as nutrients deplete), and the decline phase (toxic waste accumulation causes cell deaths to outpace new divisions).

When conditions turn harsh, such as during severe drought or starvation, certain rod-shaped bacteria (notably Bacillus and Clostridium) protect themselves by forming an endospore. The cell encases a copy of its DNA inside a tough, dehydrated protein coat. Normal boiling at 100°C will not kill these spores. When favourable warmth and moisture return, the endospore germinates back into an active, vegetative bacterial cell. In commercial canning, food is heated to 121°C under pressure for at least 3 minutes to destroy Clostridium botulinum spores.

Food Poisoning: Infectious vs Toxic Pathogens

Food poisoning is an acute illness caused by eating food contaminated by bacteria, biological toxins, or chemicals. The Leaving Certificate requires you to understand the biological difference between infectious and toxic food poisoning.

Infectious food poisoning happens when you eat food containing living pathogenic bacteria. Once swallowed, the live cells travel to your intestines, multiply, and release endotoxins as they die and break down. Because the bacteria need time to establish themselves in the digestive tract, the incubation period is relatively slow, taking roughly 12 to 36 hours. A classic example is Salmonella.

Toxic food poisoning happens when you consume food containing poisonous exotoxins that were secreted directly into the food by bacteria growing on it before the food was eaten. Because the toxic chemical is already formed, it irritates the stomach lining almost immediately, producing a rapid onset of symptoms within 1 to 6 hours (often around 2 hours). A classic example is Staphylococcus aureus. The exotoxin made by Staphylococcus aureus is heat-stable, so boiling the food may kill the bacteria but leave the poison intact.

Profiles of Three Key Pathogens

• Salmonella (Infectious):** Gram-negative, rod-shaped bacillus, facultative anaerobe, and mesophile. Its main habitats are the gut of poultry, farm animals, and humans, as well as untreated water. High-risk foods include raw or undercooked poultry, unpasteurised eggs, and raw minced meat. Symptoms appear in 12 to 36 hours and include diarrhoea, abdominal cramps, vomiting, and fever. Prevent it by cooking poultry and eggs to a core temperature of 75°C and using separate red chopping boards for raw poultry.
• Staphylococcus aureus (Toxic):** Gram-positive, spherical coccus arranged in grape-like clusters, facultative anaerobe, and mesophile. It lives on human skin, in the nose, throat, boils, and open cuts. High-risk foods are cooked foods handled after cooking, such as sliced ham, cream pastries, and sandwich fillings. The incubation period is 1 to 6 hours, producing projectile vomiting and severe abdominal pain, often with a subnormal body temperature and no fever. Prevent it by covering all cuts with waterproof blue plasters, not touching hair or face, and chilling cooked dishes below 5°C.
• Listeria monocytogenes (Infectious):** Gram-positive, rod-shaped, non-sporing bacillus, facultative anaerobe, and mesophile that is psychrotrophic (able to grow at refrigeration temperatures between 0°C and 5°C). It is widely found in soil, animal manure, sewage, and unwashed raw vegetables. High-risk foods include soft unpasteurised cheeses (brie, camembert), pâté, and pre-packed cooked meats. The incubation period can range from several days up to several weeks. It causes flu-like chills and fever, but poses extreme danger to pregnant women because it can cross the placenta and cause miscarriage, stillbirth, or severe neonatal meningitis.

Fungi: Moulds, Large Fungi, and Yeasts

Fungi are plant-like organisms that lack chlorophyll. Because they cannot manufacture their own carbohydrates by photosynthesis, they live as saprophytes (feeding on dead organic matter) or parasites.

Moulds

Moulds consist of branching microscopic threads called hyphae. These hyphae grow over and through food, secreting digestive enzymes and absorbing broken-down nutrients. Together, they form a dense, visible, furry carpet called a mycelium.

• Phycomycetes (e.g. Mucor): These moulds have non-septate hyphae, meaning the filaments are continuous hollow tubes without internal dividing walls. They reproduce asexually by growing upright stalks called sporangiophores, which develop round, closed spore cases called sporangia at the tip. When ripe, the sporangium bursts and scatters sporangiospores. Mucor* forms fluffy, cotton-wool-like growth on stale bread and soft fruit.
• Ascomycetes (e.g. Penicillium, Aspergillus): These moulds have septate hyphae, where the threads are divided into distinct cellular compartments by cross-walls called septa. They reproduce asexually by producing chains of naked spores called conidia from the tips of branched, brush-shaped stalks called conidiophores. Penicillium produces flat, powdery blue-green circles on citrus rinds and hard cheeses. Aspergillus grows on damp grains, nuts, and dried fruit, producing dangerous carcinogenic toxins known as aflatoxins*.

Large Fungi (Basidiomycetes)

Edible mushrooms and wild toadstools are large macroscopic fungi. Below the ground or inside rotting wood, an extensive feeding mycelium develops. When mature, it sends up a fleshy fruiting body consisting of a stalk (stipe) and an umbrella-shaped cap. Microscopic club-shaped structures called basidia line the gills under the cap and release reproductive spores into passing air currents.

Yeasts

Yeast (Saccharomyces cerevisiae) is a single-celled microscopic fungus with an oval shape. Under a microscope, you can identify its outer cell wall, cell membrane, cytoplasm, distinct nucleus, clear vacuole, and circular bud scars.

• Reproduction by Budding: In warm, moist, sugary conditions, yeast reproduces asexually. A small outward bulge forms on the parent cell wall. The nucleus divides by mitosis, and one daughter nucleus moves into the swelling bud. A wall forms across the narrow neck, and the new cell pinches off, leaving a bud scar on the parent.
• Fermentation: When oxygen is shut out during bread-making or brewing, yeast switches from aerobic respiration to anaerobic fermentation. Using its natural enzyme complex zymase, it converts simple sugars into ethanol, carbon dioxide, and energy:

In bread-making, the carbon dioxide bubbles become trapped inside the stretchy gluten network, expanding during baking to make the loaf rise. The small amount of alcohol evaporates off in the hot oven.

Food Spoilage and Preservation Principles

Food spoilage refers to any unpleasant change in a food's colour, flavour, texture, or smell that makes it unpalatable or unsafe to eat. It is caused by living micro-organisms, natural enzymes, or physical and chemical factors:

• Moisture loss: Produce shrinks and wrinkles.
• Rancidity: Fats react with oxygen, causing off-flavours.
• Physical damage: Bruising breaks cells, releases enzymes and lets microbes in.

Spoilage Caused by Enzymes

Enzymes are natural protein catalysts present inside all plant and animal tissues. They do not stop working when a plant is picked or an animal is slaughtered. Left unchecked, they cause spoilage in three main ways:

1. Over-ripening: Ripening enzymes continue breaking down carbohydrates and cell walls well past peak eating quality, leaving fruit soft, mushy, and decayed (e.g. a firm banana turning brown and collapsing into liquid).
2. Enzymic Browning: When plant cells are sliced or bruised, cell walls tear open and release the enzyme oxidase. In the presence of atmospheric oxygen, oxidase reacts with phenolic compounds in the plant to produce brown melanin pigments. This is why cut raw apples and peeled potatoes turn brown when exposed to air.
3. Enzymic Deterioration: Some enzymes continue working even at freezing or chill temperatures. Enzymes in oily fish break down fats and proteins to create rancid off-odours in the fridge, while unblanched frozen vegetables lose their bright colour and vitamin C because plant oxidases stay active.

We control enzymes by altering their environment: heat above 70°C denatures them permanently (e.g. blanching vegetables before freezing), cold below 5°C slows their action, acids like lemon juice drop the pH below their working range, and covering cut fruit with water stops oxygen from reaching the oxidase enzymes.

Spoilage Caused by Micro-organisms

Microbes decompose food nutrients to fuel their own growth:

• Putrefaction: Anaerobic bacteria break down animal proteins into foul-smelling nitrogen and sulphur compounds, such as hydrogen sulphide, producing the rotten smell of decaying meat and fish.
• Souring / Acid Fermentation: Lactic acid bacteria ferment lactose milk sugar into lactic acid. The falling pH causes the milk protein casein to curdle and turn sour.
• Surface Slime and Discolouration: Bacteria multiply into sticky, moist layers of slime on cold stored meats, while moulds grow visible velvety spore colonies over bread, soft fruit, and cheese rinds.

Principles of Food Preservation

Every food preservation technique works by altering or removing at least one condition that microbes and enzymes need to survive:

• Heat Processing: High temperatures denature enzyme proteins and destroy microbial cells. Milk pasteurisation heats milk to 72°C for 15 seconds to kill pathogens, while pressure canning heats food to 121°C to destroy heat-resistant bacterial endospores.
• Cold Storage: Refrigeration (0°C to 5°C) slows down microbial multiplication and enzyme activity. Deep freezing (-18°C) solidifies liquid water into ice, making water unavailable and forcing cells into dormancy.
• Dehydration: Removing water drops the water activity ($a_w$) below what microbes require to transport nutrients across their cell membranes (e.g. dried milk powder and instant soup).
• High Solute Concentrations (Osmosis): Adding high levels of sugar (jam containing 65% sugar) or salt (cured bacon) creates a concentrated solution around the food. Water is drawn out of microbial cells by osmosis, causing them to shrivel and become inactive.
• Acid Addition (Lowering pH): Pickling uses vinegar (ethanoic acid) to drop the pH below 4.5. This denatures bacterial enzymes and prevents microbial multiplication.

Beneficial Uses of Micro-organisms in Food

Not all micro-organisms cause disease or spoil food. Many are carefully cultivated in commercial food production to create distinct flavours, textures, and products:

• Cheese Production: Lactic acid bacteria (Lactococcus lactis) are added to milk to convert lactose into lactic acid, providing the mild acidity needed for the enzyme rennet to coagulate milk into curds and whey. In blue cheeses, spores of the mould Penicillium roqueforti are added to the milk or curd; the cheese is later pierced so air can enter, allowing the mould to grow into colourful blue veins and sharp flavours, while Penicillium camemberti forms the soft, edible white rind on brie and camembert.
• Yoghurt Manufacture: Pasteurised whole or skimmed milk is inoculated with two specific thermophilic bacteria: Lactobacillus bulgaricus and Streptococcus thermophilus. The milk is held at 42°C, allowing the bacteria to ferment lactose into lactic acid. This mild acid coagulates the milk proteins into a smooth, thick gel and gives yoghurt its characteristic clean, tangy taste.
• Vinegar Manufacture: Acetic acid bacteria (Acetobacter) convert dilute alcohol from fermented apples (cider) or wine into ethanoic acid in the presence of oxygen.
• Novel Protein (Mycoprotein): The micro-fungus Fusarium venenatum is grown inside large, continuous fermentation tanks supplied with glucose syrup and oxygen. The resulting filamentous biomass is harvested, bound with egg albumen, and textured into Quorn products, providing an alternative protein source high in dietary fibre and low in saturated fat.

Mechanisms of Food Spoilage

Food spoilage is any disagreeable change in a food's normal state that makes it unpalatable or unsafe. You can usually detect these changes through sight, smell, taste, or texture.

1. Microbial Spoilage

Micro-organisms feed on nutrients in food and release metabolic waste products that cause off-odours, slimy surfaces, and sour flavours.

• Bacteria: Single-celled organisms that break down dietary proteins through putrefaction. They decompose amino acids to release foul-smelling compounds like hydrogen sulphide and ammonia.
• Yeasts: Single-celled fungi that ferment simple sugars into carbon dioxide and ethanol. This fermentation causes gas bubbles, alcohol taints, and souring in foods such as fruit juices and jams.
• Moulds: Multicellular fungi that form visible, fuzzy colonies on bread, soft fruit, and cheese. Their growth develops from thread-like networks called mycelia.

2. Enzymatic Spoilage

Enzymes are natural biological catalysts found in all plant and animal tissues. They remain active after harvesting or slaughter and drive continuous chemical changes.

• Over-ripening: Enzymes break down insoluble protopectin into soluble pectin and eventually into pectic acid. This breakdown softens plant cell walls until the fruit turns mushy and decays.
• Enzymic browning: Slicing or bruising plant tissues damages cells and exposes them to oxygen. Oxidase enzymes, such as polyphenol oxidase, react with oxygen and natural phenolic compounds to produce dark melanin pigments. Coating sliced apples with lemon juice lowers the surface pH, which denatures the oxidase and stops the discolouration.
• Low-temperature activity: Some enzymes stay active even in cold storage. Natural enzymes in fish cause flesh softening and off-odours inside domestic refrigerators. In unblanched frozen vegetables, active oxidases continue to destroy vitamin C and fade green chlorophyll.

3. Moisture Loss and Chemical Spoilage

• Moisture loss: Evaporation draws water out of food surfaces. Leafy vegetables wilt rapidly and citrus fruits develop wrinkled, dry skins when stored in dry air.
• Rancidity: Atmospheric oxygen reacts with unsaturated fatty acids in fats and oils (oxidative rancidity). This oxidation creates unpleasant, sharp flavours and stale odours in butter, nuts, and cooking oils.
• Physical damage: Bruising or punctures from transport break cell membranes. This damage exposes inner tissues to ambient oxygen, speeding up both enzymatic browning and microbial infection.

Factors Affecting Microbial Growth: Bacteria, Moulds, and Yeasts

Micro-organisms need specific environmental conditions to survive and multiply. Every preservation technique works by removing at least one of these necessities.

Factors Affecting Bacterial Growth

• Temperature: Bacteria are grouped by the temperatures at which they grow best:
• Psychrophiles: grow between 0°C and 20°C, causing spoilage in cold stores.
• Mesophiles: thrive between 20°C and 45°C, with an optimum around 37°C (human body temperature). Most food poisoning bacteria belong here.
• Thermophiles: prefer high temperatures between 45°C and 75°C.
• The danger zone is 5°C to 63°C. In this range, food poisoning bacteria multiply rapidly. Below 5°C their growth becomes dormant, while temperatures above 63°C begin to destroy active vegetative cells.
• Moisture: Bacteria absorb nutrients in liquid form through their cell membranes, so they require available water ($a_w \ge 0.91$) to multiply.
• Oxygen:
• Obligate aerobes: must have oxygen to survive.
• Obligate anaerobes: grow only where oxygen is completely absent, such as sealed cans (Clostridium botulinum).
• Facultative anaerobes: adapt to grow with or without oxygen (Salmonella, Staphylococcus aureus).
• pH: Most pathogenic bacteria prefer neutral conditions (pH 6.6–7.5). High acid levels (pH below 4.5) inhibit their growth.
• Nutrients: Bacteria need sources of carbon, nitrogen, vitamins, and minerals. Moist, protein-dense foods like meat, poultry, shellfish, eggs, and dairy are known as high-risk foods.
• Time: Under ideal conditions, bacteria reproduce by binary fission every 20 minutes. A bacterial population follows four growth phases: lag phase (adapting to conditions), log phase (rapid exponential multiplication), stationary phase (cell divisions equal cell deaths as nutrients drop), and decline phase (waste accumulation causes numbers to plummet).

When living conditions turn harsh, genera such as Clostridium produce heat-resistant spores. These dormant survival capsules survive boiling water and germinate back into active vegetative cells once the temperature drops into the danger zone.

Moulds and Yeasts

• Moulds: Multicellular fungi made of microscopic threads called hyphae. These hyphae weave together into a vegetative mat called a mycelium. Upright hyphae form spore cases (sporangia) that burst when mature, dispersing airborne spores that settle on food. Moulds need oxygen, grow best between 20°C and 30°C, and tolerate drier, more acidic foods than bacteria. Certain moulds produce poisonous substances called mycotoxins, like aflatoxins on peanuts.
• Yeasts: Unicellular fungi that reproduce by budding, where a parent cell develops an outgrowth, transfers a copy of its nucleus, and pinches off. Yeasts thrive between 25°C and 30°C in moist, sugary, acidic foods such as fruit purees. They can grow in both aerobic and anaerobic conditions.

Useful Micro-organisms in Food Production

• Bacteria: Lactic acid bacteria turn lactose into lactic acid to make yogurt and cheese.
• Yeast: Yeast ferments sugar to carbon dioxide (which raises bread) and alcohol (beer, wine).
• Moulds: Penicillium moulds ripen blue cheeses such as Cashel Blue, and the mould Fusarium venenatum is grown to make mycoprotein (Quorn).

Food Poisoning: Infectious vs Toxic Pathogens

Food poisoning is an acute illness caused by eating food contaminated with pathogenic bacteria, bacterial toxins, toxic chemicals, or natural biological poisons like green potato solanine.

Infectious vs Toxic Bacterial Food Poisoning

Bacterial food poisoning occurs through two completely different biological pathways:

Profiles of Major Food Poisoning Bacteria

• Salmonella: Gram-negative, rod-shaped, non-spore-forming facultative anaerobe*. Habitat: intestines of humans, birds, and animals, plus untreated water. High-risk foods: undercooked poultry, raw eggs, raw milk. Optimum temperature: 37°C. Incubation: 12–36 hours. Symptoms: diarrhoea, abdominal cramps, fever, nausea, and vomiting.
• Listeria monocytogenes:* Gram-positive, rod-shaped, non-spore-forming bacterium. Habitat: soil, animal manure, sewage, unpasteurised milk. It is psychrotrophic, meaning it continues to multiply at fridge temperatures below 5°C. High-risk foods: soft cheeses, deli meats, ready-to-eat salads, unpasteurised dairy. Incubation: 1 to 70 days. Symptoms: flu-like fever and aches, with severe risks of miscarriage or meningitis in pregnant women and newborns.
• Staphylococcus aureus:* Gram-positive spherical bacterium (coccus) that does not form spores. Habitat: human skin, nose, cuts, boils. High-risk foods: hand-prepared foods served cold, such as sliced ham, cream pastries, potato salad. It produces heat-stable exotoxins. Incubation: 1–6 hours. Symptoms: severe vomiting, stomach cramps, mild diarrhoea.
• Clostridium botulinum:* Gram-positive, spore-forming, obligate anaerobe. Habitat: soil, lake mud, fish intestines. High-risk foods: home-canned low-acid vegetables, vacuum-packed fish, honey (for babies under one year only). It produces a lethal neurotoxin. Incubation: 12–36 hours. Symptoms: double vision, swallowing problems, paralysis, respiratory failure.

Principles and Methods of Food Preservation

Preservation slows down or halts food decay by making conditions unliveable for micro-organisms and destroying active enzymes.

Core Preservation Principles

• Temperature control: Chilling (0°C–5°C) slows microbial growth; freezing (−18°C) halts growth and turns liquid water to ice; heating above 75°C denatures proteins to kill vegetative cells.
• Moisture control: Removing water stops microbes from absorbing dissolved nutrients. Dehydration removes water by evaporation, while high salt or sugar concentrations draw water out of cells by osmosis.
• pH modification: Adding acid lowers the pH below 4.5, which denatures microbial enzymes and stops bacterial growth.
• Oxygen removal: Vacuum sealing, canning, and modified atmosphere packaging exclude atmospheric oxygen to stop aerobic spoilage.

Industrial Preservation Methods

• Freezing: Commercial methods include blast freezing with cold air streams, plate freezing between refrigerated metal shelves, and cryogenic immersion in liquid nitrogen at −196°C. Quick freezing produces small ice crystals that leave cell walls intact, whereas slow freezing creates large crystals that pierce cells, causing drip loss when thawed.
• Heat processing:
• Pasteurisation: Milk is heated to 72°C for 15 seconds, then chilled below 10°C. This destroys disease-causing bacteria with only a slight loss of vitamins B and C, giving refrigerated milk a shelf life of several days.
• Sterilisation: Food is heated to 110°C–120°C for 20–30 minutes to kill all vegetative microbes and spores, though it degrades heat-sensitive vitamins and alters flavour.
• Ultra-Heat Treatment (UHT): Liquid foods are heated to 132°C–140°C for 1–3 seconds and sealed into sterile cartons. This gives up to six months of ambient shelf life with good flavour retention.
• Canning: Food in sealed metal cans is heated under steam pressure to 121°C to destroy Clostridium botulinum spores. Swollen, dented, or leaking cans indicate gas-producing spoilage and must be thrown away.
• Dehydration: Industrial drying uses hot air tunnels, spray drying (misting milk into heated chambers to yield milk powder), or Accelerated Freeze Drying (AFD). In AFD, frozen food sits in a vacuum chamber with gentle heat. Ice sublimates directly into vapour without melting, leaving the food's cellular structure, colour, and taste intact.
• Chemical preservation: Permitted additives inhibit microbes, such as sulphur dioxide ($E220$) in dried fruit or sodium benzoate ($E211$) in fizzy drinks.
• Fermentation: Beneficial microbes convert sugars into organic acids or alcohol. In yogurt, lactic acid bacteria convert lactose into lactic acid, lowering the pH to prevent spoilage.
• Irradiation: Food is exposed to measured gamma rays from cobalt-60. The radiation damages the DNA of insects, bacteria, and moulds without making the food radioactive. Irradiated food must be labelled 'irradiated' or 'treated with ionising radiation'; the Radura symbol may also be shown.

Comparative Evaluation of Preserved Vegetables

Two Home Preservation Methods

Method 1: Home Freezing of Vegetables

• Procedure: Wash, peel, and trim fresh vegetables. Blanching: Submerge the pieces in boiling water for 1–4 minutes, then plunge them into an ice-water bath to stop the cooking. Drain thoroughly, spread on trays to freeze individually, pack into moisture-vapour-proof freezer bags, squeeze out excess air, label with the contents and date, and freeze quickly at −25°C. Store at −18°C.
• Principle: Blanching heat denatures and destroys ripening enzymes like oxidase. Freezing food to −18°C halts bacterial growth and locks liquid water into ice crystals, depriving microbes of moisture.
• Spoilage risks: Inadequate blanching allows surviving enzymes to degrade colour and flavour in the freezer. Poor wrapping causes moisture to sublimate from the surface, creating dry, tough, discoloured patches known as freezer burn.

Method 2: Jam Making

• Procedure: Simmer prepared fruit in a pan to soften the skins and release natural pectin. Add lemon juice if the fruit is low in acid. Add warmed granulated sugar (enough for the finished jam to contain about 60–65% sugar) and stir until completely dissolved. Boil rapidly until it reaches the setting point at 104°C (check with a cold saucer wrinkle test). Skim surface froth, pour into warm sterilised jars, seal with a waxed disc and lid, and label.
• Principle: High boiling heat destroys vegetative microbes and denatures fruit enzymes. The high sugar concentration creates high osmotic pressure, pulling water out of any microbial cells by osmosis to prevent growth. Added acid helps pectin set into a firm gel, while the airtight seal keeps out airborne spores.
• Spoilage risks: Using too little sugar lets wild moulds or yeasts ferment the jam. Unsterilised jars or loose lids let airborne mould spores enter and grow across the surface.

Food Safety, Kitchen Hygiene, and HACCP Systems

Maintaining a safe kitchen requires consistent personal hygiene, proper cleaning habits, strict temperature control, and a systematic risk plan.

Safe Food Handling and Reheating

• Storage: Keep domestic fridges between 0°C and 5°C and freezers at −18°C. Store raw meats in covered dishes on the bottom fridge shelf so drips cannot reach cooked foods. Rotate stock using First In, First Out (FIFO) and monitor dates. Store cupboards should remain clean, dry, and cool.
• Cooling leftovers: Cool hot cooked food within two hours by dividing it into shallow containers, then place it in the fridge straight away.
• Reheating: Reheat food only once, heating the core to at least 70°C–75°C. Do not reheat food in a bain-marie because it warms food too slowly and is built only for hot holding.

Personal and Kitchen Hygiene

• Personal hygiene: Wash hands with warm water and soap for at least 20 seconds before touching food, after using the toilet, and after handling raw meat or bins. Wear a clean apron, tie back hair, remove rings or watches, and cover cuts with a bright blue waterproof plaster. Anyone with vomiting or diarrhoea must stay out of the food preparation area.
• Kitchen hygiene: Wash surfaces with antibacterial spray as you work. Use colour-coded boards and knives (red for raw meat, blue for raw fish, yellow for cooked meat, green for fruit and salad, brown for unwashed root veg, white for bread and dairy). Change dishcloths daily or use disposable paper towels. Keep kitchen bins covered and empty them regularly.

HACCP Systems

Hazard Analysis and Critical Control Point (HACCP) is a systematic management system that identifies, evaluates, and controls food safety hazards. The 7 Principles of HACCP are:

1. Conduct a hazard analysis.
2. Determine the Critical Control Points (CCPs).
3. Establish critical limits for each CCP.
4. Establish monitoring procedures for CCPs.
5. Establish corrective actions when monitoring shows a CCP is out of control.
6. Establish verification procedures to confirm the system works effectively.
7. Establish documentation and record keeping.

• ISO 9000: An international quality management standard verifying that a food processing company follows documented procedures to ensure consistent quality, food safety, and regulatory compliance.

Food Additives: Functions, Origins, and Control

A food additive is any substance not normally consumed as a food by itself, intentionally added to food during processing or packaging to improve preservation, colour, flavour, or texture.

Origins of Additives

• Natural: Extracted directly from plants or animals (e.g. beta-carotene from carrots, lecithin from egg yolks).
• Nature-identical: Synthesised in a laboratory to be chemically identical to compounds found in nature (e.g. synthetic ascorbic acid).
• Artificial: Man-made chemical formulations that do not occur in nature (e.g. tartrazine $E102$, saccharin).

Functional Classes of Additives

• Preservatives: Inhibit microbial multiplication to extend shelf life. Examples: salt in bacon; sodium benzoate ($E211$) in acidic soft drinks; sulphur dioxide ($E220$) in dried fruit.
• Antioxidants: Prevent fats and oils from reacting with oxygen and turning rancid. Examples: ascorbic acid (vitamin C, $E300$) in fruit juice; butylated hydroxyanisole (BHA, $E320$) in vegetable oils.
• Colourings: Restore colour lost during heat processing or give uniform colour to food. Examples: natural beta-carotene ($E160a$) in margarine; synthetic tartrazine ($E102$) in sweets.
• Emulsifiers: Stop oil and water from separating by holding them in a stable emulsion. Example: lecithin ($E322$) in mayonnaise.
• Stabilisers: Prevent emulsions from breaking down and maintain uniform texture. Example: carrageenan ($E407$) in ice cream.
• Anti-caking agents: Stop powders from absorbing moisture and clumping into lumps. Example: silicon dioxide ($E551$) in table salt.
• Humectants: Retain moisture so baked foods do not dry out. Example: glycerol ($E422$) in cakes and icing.
• Flavourings and flavour enhancers: Flavourings supply aroma and taste (e.g. synthetic ethyl vanillin). Flavour enhancers boost the food's existing savoury notes without contributing a distinct flavour of their own (e.g. monosodium glutamate, MSG, $E621$).
• Sweeteners: Add sweetness with few or no calories. Intense sweeteners (e.g. aspartame, $E951$) are hundreds of times sweeter than table sugar; bulk sweeteners (e.g. sorbitol, $E420$) provide volume and chewiness in sugar-free gum.
• Nutritive additives: Fortify foods to replace nutrients lost during processing or address population deficiencies. Examples: vitamin D added to milk; folic acid added to breakfast cereals.

Weighing Additive Use: Advantages vs Disadvantages

• Advantages: Prevents spoilage, reduces household food waste, safeguards against food poisoning, restores appetizing colours, and provides low-sugar choices for diabetics.
• Disadvantages: Some additives trigger sensitivities (e.g. sulphites triggering asthma attacks, synthetic colours linked to hyperactivity); they can mask poor-quality raw ingredients; aspartame is dangerous for individuals with phenylketonuria (PKU).

Legal Control of Additives

Under European Union regulations, additives are strictly managed:

• The European Food Safety Authority (EFSA) assesses toxicity data and sets an Acceptable Daily Intake (ADI) for every substance.
• Approved additives receive an E-number, proving they have passed safety assessments and are permitted only in specific foods at measured levels.

Food Legislation and Consumer Protection Agencies

National laws and European directives work alongside state inspection bodies to safeguard consumer health across Ireland.

Core Food Legislation

• Sale of Food and Drugs Acts (1875, 1879, 1899, 1936): Foundational consumer laws that make it an offence to adulterate food with harmful additives or sell food that is not of the nature, substance, or quality demanded by the shopper.
• Food Hygiene Regulations (1950–1989): Set mandatory hygiene standards for Irish food premises. They required food businesses to register with local health boards, made selling contaminated food illegal, excluded infected staff from food preparation areas, and gave inspectors the legal power to close down unhygienic kitchens. These rules have since been replaced by EU Regulation 852/2004 on the hygiene of foodstuffs, which requires HACCP-based procedures and staff training.
• Health (Official Control of Foodstuffs) Regulations 1991: Put EU food control rules into Irish law. They empower Environmental Health Officers (EHOs) to inspect food premises at any stage of manufacturing, take samples for laboratory testing, inspect business records, and seize unsafe food.
• Labelling Regulations (1982 and 1991; updated by EU No 1169/2011): Require pre-packaged food to display clear information: the name of the food, an ingredients list in descending order by weight, allergens highlighted in bold, net quantity, best-before or use-by dates, storage requirements, and manufacturer details.
• Use-by date: Applied to perishable foods (e.g. fresh poultry, milk); eating food past this date carries an immediate health risk.
• Best-before date: Relates to optimal sensory quality and texture (e.g. dry biscuits, canned fruit); food eaten past this date is safe to eat, although its quality may drop.

Irish Food Safety Agencies

• Food Safety Authority of Ireland (FSAI): The national body that coordinates the enforcement of food safety legislation across Ireland. It manages service contracts with statutory enforcement bodies (like the HSE), issues public food recalls, advises the Minister for Health, and supports commercial food businesses in setting up HACCP systems.
• Department of Agriculture, Food and the Marine (formerly Department of Agriculture, Food and Rural Development): Enforces standards across farms, abattoirs, and meat plants. It oversees veterinary inspections and checks meat and dairy for pesticide, antibiotic, and chemical residues.
• Department of Health (formerly Department of Health and Children): Drafts national food safety legislation and sets public health nutrition guidelines.
• Health Service Executive (replacing Regional Health Boards): Employs Environmental Health Officers (EHOs) who carry out routine inspections of restaurants, caterers, and supermarkets, take food samples for analysis, investigate food poisoning outbreaks, and issue closure orders.
• Public Analyst Laboratories: State laboratories run by the HSE that analyse food and water samples submitted by EHOs. They test for chemical toxins, microbial pathogens, illegal additives, and packaging label accuracy.
• Competition and Consumer Protection Commission (incorporating the Director of Consumer Affairs): Protects consumer rights by enforcing fair trading laws, prosecuting misleading advertising, and ensuring food packaging descriptions are accurate.

Key terms

Binary Fission

A form of asexual reproduction in bacteria where a single cell duplicates its circular DNA and divides into two identical daughter cells.

Endospore

A tough, dormant, heat-resistant structure formed inside certain bacteria (such as Clostridium and Bacillus) that withstands drought and boiling.

Exotoxin

A soluble protein poison secreted into food by living bacteria as they grow, causing toxic food poisoning with rapid onset.

Endotoxin

A toxin held within bacterial cells and released into the gut only when the bacteria multiply, die, and break down.

Danger Zone

The temperature range between 5°C and 63°C in which food poisoning bacteria multiply rapidly.

Water Activity (aw)

A measurement of unbound water in food available to support microbial metabolism, scored on a scale from 0.0 to 1.0.

Hyphae

Microscopic, thread-like filaments that absorb nutrients and make up the growing structure of a mould.

Mycelium

A dense, visible, intertwined network of fungal hyphae that forms the fuzzy growth on mouldy food.

Budding

An asexual process in yeast where a daughter cell grows outward as a bud from the parent cell wall before separating.

Zymase

The natural enzyme complex in yeast that ferments simple sugars into ethanol and carbon dioxide under anaerobic conditions.

Enzymic Browning

A chemical reaction where the enzyme oxidase in damaged plant cells reacts with atmospheric oxygen to produce dark melanin pigments.

Putrefaction

The anaerobic decomposition of proteins by bacterial enzymes, generating foul-smelling compounds like hydrogen sulphide.

Aflatoxins

Poisonous, carcinogenic toxins produced by Aspergillus moulds on improperly dried nuts, seeds, and grains.

Mesophile

A micro-organism that grows best at moderate temperatures between 20°C and 45°C, with 37°C being optimum.

Putrefaction

The decomposition of proteins by bacteria under anaerobic conditions, producing foul-smelling compounds like hydrogen sulphide and ammonia.

Enzymic Browning

A chemical reaction in cut or damaged plant tissue where oxidase enzymes react with phenolic substances and oxygen to create dark melanin pigments.

Danger Zone

The temperature band between 5°C and 63°C where food poisoning bacteria multiply most rapidly.

Infectious Food Poisoning

An illness caused by eating live pathogenic bacteria that establish in the intestine and release endotoxins as they die.

Toxic Food Poisoning

An illness caused by ingesting preformed exotoxins produced by bacteria while multiplying on food before it is eaten.

Facultative Anaerobe

A micro-organism capable of surviving and multiplying both in the presence and in the complete absence of atmospheric oxygen.

High-Risk Foods

Moist, protein-rich foods such as poultry, seafood, dairy, and eggs that support rapid bacterial multiplication.

Blanching

Immersing vegetables briefly in boiling water and then plunging them into ice water to denature ripening enzymes before freezing.

Osmosis

The movement of water molecules across a semi-permeable membrane from a low solute concentration to a high solute concentration, used in salting and jamming to dehydrate microbial cells.

HACCP

Hazard Analysis and Critical Control Point; a systematic preventive food safety management system that identifies, evaluates, and controls hazards.

Critical Control Point (CCP)

A specific stage in food preparation where a control measure must be applied to prevent, eliminate, or reduce a food safety hazard to a safe level.

E-Number

An identification code assigned to a food additive indicating it has undergone safety assessments by EFSA and is approved for use across the EU.