Soured milk and yoghurt
The materials required for construction are:
Aluminium bar 1.25 x 1.25 cm, 3.65 m lengths (½” x ½”, 12 ft lengths).
Aluminium bar 1.9 x 1.9 cm, 3.65 m lengths (¾” x ¾”, 12 ft lengths).
Aluminium ‘T’ Sections 2.54 x 2.54 cm, 3.65 m lengths (1” x 1”, 12 ft lengths).
Aluminium ‘U’ Section 3.65 m lengths (12 ft lengths).
Aluminium sheets 20-gauge 20 cm x 10 cm (8" x 4").
Welded Mesh 75 mm.
Light bulbs 40W.
Dial thermometer 0 - 100 oC.
Electric fan, low profile vertical operation box fan.
Rigid foam insulation, wires, teflon sleeving, connectors, self tapping screws as
240V electricity supply, floor area 60 cm x 122.5 cm.
The incubator frame is rectangular with the glass sheet at the front. The thermostat is attached
to the external frame. Bulbs are placed at the base of the incubator. The incubator has 2
chambers with 6 trays each. Each tray holds 42 pots (500 pots per batch). Technical drawings
are available from Practical Action South Asia.
The main quality factors for soured milk and yoghurt are the colour, taste and texture. The colour
should remain unchanged during processing. The taste and texture both depend on the amount
of lactic acid produced during the fermentation and this in turn depends on the amount of
inoculum added to the milk, and the temperature and time of incubation. In flavoured or fruit
yoghurt, the colour and flavour depend on the type and amount of added essence, colouring or
Packaging and storage control
The products require protection against dust and insects during distribution and retail display.
Traditionally, covered clay pots, gourds and wooden or ceramic bowls have each been used and
these are suitable provided proper hygiene and cleaning are observed, particularly if they are to
be reused. Plastic pots are more hygienic, more attractive to consumers, more convenient to use
and easily sealed with a foil cover or clip-on plastic lid. Other alternatives are returnable glass
jars or waxed paperboard cups. Products should be stored in a cool place away from sunlight
and preferably in a refrigerator at 4-8 oC.
Soured milk and yoghurt are low- to medium-risk
products that can easily be made at a small scale.
They often have a high demand and different flavours
can be produced to give a range of products.
Fig. 1. Yoghurt pot sealer.