Fruit juice processing
Practical Action
In all cases, sugar should be added to the fruit juice as a sugar syrup. The syrup should be
filtered through a muslin cloth prior to mixing to remove particles of dirt which are always
present. This gives a clearer, higher quality product.
Pasteurisation
All the products mentioned above need to be pasteurised at 80-95°C for 1-10 minutes prior to
hot-filling into bottles. At the simplest level, this may be carried out in a stainless steel,
enamelled or aluminium saucepan over a gas flame, but this can result in localised overheating
at the base of the pan, with consequent flavour changes.
Care is needed when producing pineapple juice due to a heat resistant enzyme in the juice. The
enzyme damages skin after prolonged contact and workers should therefore wear gloves to
protect their hands. The juice must be heated to a higher temperature for a longer time to
destroy the enzyme (eg boiling for 20 minutes).
It is best to use stainless steel pans to heat fruit juice as the acidity of the juice can react with
aluminium in aluminium pans during prolonged heating. However, large stainless steel pans are
very expensive and may not be affordable by the small scale processors. To get round this
problem, it is possible to use a large aluminium pan to boil the sugar syrup. The boiling syrup
can then be added to a given amount of fruit juice in a small stainless steel pan. This increases
the temperature of the juice to 60-70°C. The juice/syrup mixture is then quickly heated to
pasteurising temperature.
Bottle size (litres) Pasteurisation time
at 80°C (minutes)
0.33
10
0.5 15
0.75
20
Table 1: Pasteurisation times at 80°C for different bottle sizes
Another option is to pasteurise the juices once they have been bottled. The bottles are placed in
a hot water bath which is heated to 80°C. The bottles are held in the hot water for the given
amount of time until the contents reach the desired temperature. The length of time required in
the water bath depends on the size and volume of the bottles (see table 1). A thermometer
should be placed in one of the bottles, which is used as a test bottle per batch, to monitor the
temperature and to ensure that the correct temperature has been reached. This method of
pasteurisation has benefits but also has problems.
Benefits
Juice is pasteurised within the bottle so
the chance for re-contamination of the
juice is reduced
No need for large stainless steel pans for
pasteurisation
Problems
Difficult to ensure the internal temperature
of the bottles reaches the desired
pasteurising temperature
Require glass bottles for pasteurising
Table 2: The pros and cons of pasteurising within after bottling
The next industrial jump in pasteurisation is an expensive option that involves the purchase of a
double-jacketed steam kettle in stainless steel and a small boiler. The total cost is likely to be in
the region of £5-10,000, which is only viable for larger scale operations.
4