Preservation and Shelf-life

Yeast -

• fermentation - sugar ---> alcohol + carbon dioxide 
• bread, alcohol 
• conditions: 
  • warm
  • moist
  • no oxygen 

Moulds - 

• produce specific flavours and textures 
• cheese
• spoilage:
  • thread-like filaments 
  • reproduce by producing spores 
  • harmful - produce myotoxins 
• conditions:
  • moist
  • 20-30°C
  • acid, alkaline, salt or sugar foods 

Bacteria - 

• used in food manufacture 
• cheese, yogurt 
• spoilage - 
  • often undetected - looks, taste and smells the same 
  • pathogenic - cause food poisoning - e.g. E-coli 
• conditions - 
  • warmth - optimum 37 ° C
    • danger zone 5 ° C - 65 ° C
  • moisture 
  • food
  • oxygen - not all require oxygen 
  • neutral pH 
  • time - reproduce rapidly 

Proteins that speed up chemical reactions 

Functions:

• bread and brewing - fermentation 
• cheese - ripening stage 

Spoilage:

• can cause 'browning' 
• Reduced by: 
  • high temperatures
  • acidic conditions 

• Raw fish 
• Dairy products
• Cooked meat and poultry
• Shellfish and seafood
• Gravies, sauces, stocks, soups, and stews 
• Egg [roducts 
• Cooked rice
• Protein-based baby foods 

• high acid content foods 
  • pickled, chutney, fruit juice
• high sugar content foods 
  • marmalades, jams, fruit packed syrup 
• sugar based confectionary 
  • sweets, icing 
• unprocessed raw vegetables 
  • potatoes, carrots 
• edible oils and fats 

Fridge:

• avoid opening the door regularly 
• avoid putting in hot food - raises temperature - steam - condenses - raises temperature of other foods - bacterial growth 
• cover food

Freezer:

• freezer 'star' rating - temperature range
• thawing and refreezing - structure is damaged - loss of colour, flavour, texture, nutrition - bacteria grow quickly in thawed foods 
• foods with a large proportion of water - delicate structure - ice crystals damage cell structure - collapse - don't freeze well 
• freezer burn - greyish white marks when food has been packaged badly - dehydrates - safe to eat - loss of flavour, colour and texture 

Vinegar - 

• acid - pH 3.5 
• bacteria cannot survive below 4.5 
• pickled onions, cabbage, eggs 

Salt - 

• ham, bacon, fish 
• brine solution - tuna, vegatables
• reduced moisture content - osmosis 

Sugar - 

• high concentrations - absorbs water - stops bacteria growing 
• jams, marmalade, jellies 
• coating candies, crystallised fruit 

Additives - 

• destroy bacteria - prevent them reproducing 

Modified Atmosphere Packaging (MAP) 

• altering gas - prevents bacteria - longer shelf life 
• controlled atmosphere packaging (CAP) 
• oxygen, nitrogen and carbon dioxide 
• process: 
  • package fresh foods in peak conditions 
  • once opened - has normal shelf life
  • replacing air - by 'gas flashing' 
  • sealing the plastic bag or lid to food tray by hermetic sealing process 
• can see the product 
• chilled meats, vegetables - lettuce, fruits 

Vacuum packed - 

• remove air - prevents bacteria 
• once opened - normal shelf life 
• anaerobic conditions 
• maintains colour and texture 
• bacon, smoked fish 
• Coffee - Accelerated Freeze Dried (AFD) - vacuum packed - doesn't lose taste