HEAT TREATMENTS Fruit and vegetables can be preserved at home using high temperatures. Methods used are: jam - making, chutney - making and bottling.
JAM MAKING Jam is cooked fruit boiled with 65% sugar.
HOW SUGAR PRESERVES FOOD Sugar dissolved in food forms a solution with a low water concentration. Microbial cells have a high water concentration and the cells are enclosed by a semi-permeable membrane. The water is drawn out of the microbial cells by osmosis and the cells are dehydrated and destroyed.
PRINCIPLES OF JAM - MAKING High temperatures are used to destroy enzymes and microbes in the fruit. Jam is sealed in pots to prevent re-entry of microbes. 65% sugar prevents microbes growing in jam once opened. Pectin, acid and sugar make jam set.
WHAT IS NEEDED FOR GOOD JAM Fruit Sugar Acid Pectin
FRUIT Just ripe. Good quality. Acidic. High in pectin. If low in acid and pectin, combine with a fruit high in these e.g. apples or use jam sugar.
SUGAR Preservative. Helps setting. Too much causes crystallisation. Too little causes fermentation and jam won’t set. Jam sugar / Sure-set sugar is sugar crystals coated with pectin and acid. Using Jam sugar means a shorter boiling time and as it is purer, less scum is produced.
ACID Draws out pectin from cell walls of fruit. Prevents crystallisation. Improves colour and flavour of jam. If there is too little acid in fruit, add lemon juice, citric acid or use jam sugar
PECTIN Polysaccharide. In cell walls of ripe fruit. Fruit with a low pectin content can be combined with a high pectin fruit. Alternatively, pectin can be added or jam sugar can be used.
CHARACTERISTICS OF A GOOD JAM Clear Well set Keeps for a year Bright colour Fruity taste
EQUIPMENT Heavy based stainless steel saucepan or preserving pan. Wooden spoon. Sugar thermometer. Measuring jug. Jam jars. Jam pot covers- wax and cellophane. Elastic bands and labels.
STAGES IN JAM - MAKING Weigh fruit and sugar accurately. Jars - wash and sterilise in oven- no chips or cracks. Prepare fruit- wash, peel, remove stones & chop. Simmer fruit & water according to recipe. Add pre-warmed sugar & dissolve. Boil rapidly. Test for setting - ( temperature 105ºC, plate/wrinkle test or flake test) Skim jam & fill jars to 5mm. Cover immediately with waxed discs & cellophane. Clean jar & label - name & date. Store in a cool, dark, dry, well – ventilated area.
CHUTNEY - MAKING Chutney is fruit, vegetables or a mixture of both boiled with sugar, vinegar and spices until the mixture is thickened. Chutney is served with meat, cheese, sandwiches, salads, burgers or as an accompaniment to curry.
PRINCIPLES High temperature used to destroy enzymes and microbes. Sealing prevents recontamination. Sugar preserves by dehydrating microbial cells. Vinegar lowers pH preventing growth of microbes.
MAKING CHUTNEY Same equipment as for jam. Plastic – lined, metal jam pot lids or fabric circles steeped in melted wax are used instead of cellophane covers. These prevent evaporation. Follow recipe and method carefully. Chutney is kept for a few months before eating to let the flavour mellow.