Fruit waste utilisation
Practical Action
also possible to use ammonium sulphate (a component of fertiliser) but this cannot be recovered
and the higher cost therefore prevents its use commercially in large-scale operations.
The pectin gel is then washed and re-dissolved in water to produce a concentrated pectin
solution. It is at this stage that it is standardised or modified to give the specific properties
required. On a large-scale, it is usually dried to a powder, but on a small-scale it is possible to
add sodium benzoate preservative and sell the concentrated liquid in bottles.
Reformed fruit pieces
Fruit pulp can be recovered and formed into synthetic fruit pieces. It is a relatively simple
process but the demand for this product is not likely to be high and a thorough evaluation of the
potential market is strongly recommended before any work is undertaken.
In summary, the process involves boiling the fruit pulp to concentrate and sterilise it. Sugar may
also be added. A gelling agent, sodium alginate is then mixed with the cooled pulp this is then
mixed with a strong solution of calcium chloride. All ingredients are safe to eat and are permitted
food additives in most countries. The calcium and the alginate combine to form a solid gel
structure and the pulp can therefore be re-formed into fruit pieces. The most common way is to
pour the mixture into fruit-shaped moulds and allow it to set. It is also possible to allow drops of
the fruit/alginate mixture to fall into a bath of calcium chloride solution where they form small
grains of reformed fruit which can be used in baked goods. Commercially, the most common
product of this type is glacé cherries.
Enzymes
Commercially, the three most important enzymes from fruit are papain (from papaya), bromelain
(from pineapple) and ficin (from figs). Each is a protein-degrading enzyme used in such
applications as meat tenderisers, washing powders, leather tanning and beer brewing. However, it
is unlikely to be economic to obtain these from waste fruit. Even the more efficient collection
from fresh whole fruit is no longer economic and changes in both large-scale production (higher
quality standards and use of biotechnology to produce 'synthetic' enzymes) mean that small-scale
producers will be unlikely to compete effectively. In addition, there are moves to phase out the
use of these enzymes in food products in Europe and USA and their market is therefore declining.
In summary, these are not recommended as a means of income from waste utilisation.
Wine/vinegar
Although these products should be produced from fresh, high quality fruit juices in order to
obtain high quality products, it is technically feasible to produce them from both solid and liquid
fruit wastes. Solid wastes should be shredded and then boiled for 20-30 minutes to extract the
sugars from the fruit and to sterilise the liquid. Several batches of waste may be boiled in the
same liquid to increase the sugar concentration. This is then filtered through boiled cloth to
remove the solids and cooled ready for inoculation with yeast.
Liquid wastes should be separated during production to ensure that fruit juice is kept separate
from washwater (eg. the juice could be drained from a peeling/slicing table into a separate drum).
The juice is then boiled for 10-15 minutes and treated as above.
The liquid is then inoculated with a wine yeast (not a bread or a beer yeast) and fermented in the
normal way for wine production. This can then undergo the normal second fermentation to
produce fruit vinegar.
In summary, each of the above uses for fruit waste requires:
• a good knowledge of the potential market for products and of the quality standards required
• a careful assessment of the economics of production
• a certain amount of additional production knowledge
• a certain amount of additional capital investment in equipment
• a fairly large amount of waste to make utilisation worthwhile
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