Heat treatments like jam making and bottling can preserve fruits and vegetables at home. Jam is made by boiling fruit with 65% sugar, which kills enzymes and microbes through high heat and prevents further microbial growth due to the low water concentration caused by the sugar. Similarly, chutney is made by boiling fruits, vegetables, vinegar and spices to a thick consistency, using high heat to kill microbes and sugar and vinegar to preserve the mixture for months by lowering the pH and dehydrating microbes. Proper preparation, ingredients, and sealing of jars are needed to successfully preserve foods at home through heat treatments.

1. FOOD PRESERVATION
HEAT TREATMENTS
© PDST Home Economics

2. HEAT TREATMENTS
 Fruit and vegetables can be preserved at home
using high temperatures.
 Methods used are:
jam - making, chutney - making and bottling.

3. JAM MAKING
 Jam is cooked fruit
boiled with 65%
sugar.

4. 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.

5. 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.

6. WHAT IS NEEDED FOR
GOOD JAM
Fruit
Sugar
Acid
Pectin

7. 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.

8. 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.

9. 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

10. 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.

11. CHARACTERISTICS OF A
GOOD JAM
Clear
Well set
Keeps for a year
Bright colour
Fruity taste

12. 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.

13. 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.

14. 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.

15. 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.

16. 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.