1. Evolution of dairy development in warm countries.
2. Transition from traditional fermented milk to cultured milk with requisite quality standards.
W. Schulthess
Dairy Consultant
Karen, Nairobi, Kenya
Fresh milk turns sour if it is left to stand. This basic fact has given rise to the predilection of consumers for fermented milk such as Lassi in India, Leben in Arab countries and maziwa lala or Mala in East Africa. In keeping with the mean ambient temperatures of 15-30°C these products are predominantly the result of fermentative action by Lactobacillaceae, such as Streptococcus lactis and Streptococcus cremoris. as well as Streptococcus diacetylactis and Leuconostoc cremoris.
With the introduction of the cultivation of tea and coffee, in India in the middle of the last century and in East Africa at the beginning of this century, the consumption of tea and coffee took roots. It became a habit to consume tea with boiled fresh milk if available at reasonable cost. This called for the production of pasteurized and of sterilized milk, particularly in the fast growing urban agglomerations where consumers did not have diary cattle of their own.
Development cooperation in the second half of this century concentrated its efforts on milk collection for pasteurization and packaging in urban dairies. This invariably met with the bottleneck of big seasonal fluctuations in supply. During the rainy season production exceeds the demand of fluid milk and during dry season it falls short of fluid milk and during dry season it falls short of requirements. In the highlands of Kenya and in Zimbabwe the volume of production and the infrastructure available warrant the transformation of such surpluses into milk powder which can be used for milk toning during dry season. Where such facilities do not exist, the offer has to be brought in line the demand primarily through seasonal pricing.
The development of freeze-dried starter cultures in the period 1950 - 1970 opened the way for small, medium and large-scale manufacture of cultured milk with necessary quality assurance in warm countries. A first systematic approach was made by R.L. Kurwijila in his M.Sc thesis "Low Cost Optimisation of the flavour, consistency and keeping quality of fermented milk with particular reference to consumer acceptability in Kenya" (University of Nairobi, 1980). His investigations clearly established the predilection of the Kenyan consumer for a product containing 0.8 - 0.9% lactic acid with mild aroma (1-2 ppm) diacetyl) and adequate viscosity. The desirable vis-costly and resistance to wheying-off were obtained through denaturation of whey proteins by means of a heat treatment of the substrate at 85°C for 30 minutes or at 90 - 92°C for 10-15 minutes. R.L. Kurwijila demonstrated further that recommendations for manufacture could be applied to toned milk containing 25-50% fresh milk and 50 - 75 reconstituted milk.
Main advantages of this cultured product called Mala are:
1. Simplicity of manufacture: The mother culture can be prepared from freeze-dried commercial cultured in any clean kitchen. The mesophilic cultures applied have their temperature optimum in the ambient range of 15-30°C which makes incubators superfluous.2. Ease of preservation: Application of thermophilic cultures with a temperature optimum of 40-45°C, as required in the manufacturer of yoghurt, call not only for incubators but also for refrigeration of the product right after incubation, failing which it becomes too sour. Mesophilic cultures, such as applied in the manufacture of Mala, on the other hand, do not produce more than 1.1% lactic acid. Thus, a minimum keeping quality of 2-4 days is assured in the absence of refrigeration. However, in order to keep Mala for 2 - 3 weeks it has to be preserved at a temperature lower than 10°C. Otherwise, the development of yeast and moulds will cause off-flavours and appearance of mould mycelium at the surface.
3. Wholesomeness. The phenomenon of lactose malabsorption is fairly widespread in Africa. It causes indigestion only when fresh milk is consumed but not in the event of fermented milk products. Furthermore, Mala is a relatively cheap alternative to meat as an addition to millet or maize gruel
In 1984/85 Kenya Cooperative Creameries Ltd. (K.C.C.) introduced Mala on the Nairobi market and within 2-3 years its turn over rose from virtually zero to 60,000 - 70,000 l per day. Encouraged by this experience, a growing number of milk producers and traders are taking up small-scale manufacture of Mala in rural areas and in small townships. In doing so they are assisted by Technoserve Inc., a non-governmental organisation founded in the U.S.A.
Small, medium and large scale manufacture of Mala
For a turnover of less than 500 l milk per day the cooker depicted in Fig. 1 has proved to be particularly useful. A can holding 40-50 l milk is heated in a water bath on a wood fire under constant a stirring. After 10-15 min, at 90-92°C the can is withdrawn and placed in a water bath for cooling to 20-30°C. After inoculation and 15-20 hours incubation the coagulum is stirred to a smooth, homogenous consistency and packed.
Where the daily turnover is of the order of 500 - 3000 l/day, a vat, as depicted in Fig. 2 will be appropriate. Here the milk is heated by means of low pressure steam under constant stirring. Spray holes in the circular stem pipe ensure tangential stem jets onto the outer surface of the inner vat, allowing for uniform and effective heat transmission. Cooling can take place in either of the following ways:
1. Water enters the double jacket through the bottom inlet and through the outlet at the top it is recirculated over a re-cooling tower.2. Water from the re-cooling tower is pumped into a circular pipe at the top of the double jacket and sprayed onto the outer surface of the inner vat, where it flows down as a cooling film. After the outlet at the bottom a second pump ensures a low water level in the double jacket and recirculation over the cooling tower.
The first system can do with one pump only. The second system provides for somewhat faster cooling but it requires two pumps. A stainless steel cover on the vat minimizes yeast, and mould infection during cooling, inoculation, incubations and packaging.
Fig. 3 shows the heating, holding and cooling system in large scale operations with dairy turnovers bigger than 3,000 l/day. A plate heat exchanger with heating and regeneration sections ensures continuous operation with best possible heat economy. In a plate heat exchanger for 10,000 l/h a tubular holding section would require 385 m three-inch pipe in a insulated compartment to ensure 10 min. holding time at 90-92°C. A much cheaper alternative with lower recurring expenses for cleaning and disinfection is a holding cylinder as indicated in Fig. 3, with a booster pump at its bottom outlet for recirculation through the regeneration section and, if required, through the cooling section. Inoculation and incubation take place in suitable holding tanks made of stainless steel.
Further developments.
In 1986/87 J. Wangoh investigated the possibilities and limitations of "Flavouring the cultured milk product Mala with fruits available in Kenya" (M.Sc,.Thesis, University of Nairobi). He tested mango, pineapple, passion fruit, banana and strawberry preparations. Mango Mala proved to be the most liked. Optimum fruit additions varied between 10 and 15%+ 8-9% sugar. Heating of the fruit-sugar mix to 75°C and hot packing ensured adequate preservation.
A further M.Sc. thesis (University of Nairobi, 1988) by A.N. Gatutha dealt with the "Development of flavoured ice milk, using the cultured milk product Mala and locally available fruit juices/pulps as raw materials". Best product stability and quality with regard to overrun were obtained with 0.3% pectin or 0.3% gelatine. 25% substitution of sucrose with reducing sugars from corn syrup of 30.6 dextrose equivalent (DE) optimised sensory and physical properties. In the order of preference 20% mango pulp addition was liked best, followed by 6% pineapple juice concentrate (60°Br.) 6& passion fruit juice concentrate (45°Br. etc. Further investigations call for consideration of flavouring with lemon juice and with banana pulp.
It appears essential that more adequate attention be given to the utilization of local fruit for flavouring and to natural colouring ingredients (mulberry juice, red beet juice, Annatto seed extract etc.) Artificial flavouring and colouring ingredients should be used as supplements only.
Cultured milk can be a precursor for related products such as white cheese, cottage cheese etc. Whereas we prevent wheying off in Mala manufacture by means of appropriate heat treatment (85-92°C, 10 - 30 min.) whey separation is required in white cheese making. To this effect raw milk is subjected to pasteurisation conditions (63°C, 30 min. or 72°C, 15 - 20 sec.).
Furthermore, mesophilic cultures as used in Mala making are of paramount importance in the manufacture of Cheddar cheese. This is a product of good keeping quality and good processing characteristics suitable as an outlet for surplus milk during flush season in warm countries.
Conclusions.
Fermented milk has long been misunderstood as an outlet for milk of inferior keeping quality and the development of cultured milk was neglected. The promotion of cultured milk products holds particularly promising prospects for dairy development in warm countries with shortcomings in infrastructure such as power supply, cold chains from producer to consumer etc. However, it is by no means an alternative for processors lacking know-how and experience.
Fig 1 Cooker for small scale production of cultured milk
Basic metal structure comprising:
- ring of 4mm mild steel sheeting a.d. 69 cm, i.d. 42 cm- hot water vessel, 4mm m.s. sheeting, i.d. 40 cm, depth 60 cm, with handles for easy removal and suitable metal cover
- exit to chimney, galv. sheeting, i.d. 10 cm
- outer cover made of galv. steel sheeting, reinforced by six pcs. flat - iron 25 x 6 mm supporting metal ring by the same
- Fire door 26 x 31 cm with adjustable ventilators
- fire grate, cast iron, 20 x 27 cm
Kenyan Contractor: C. Gitundu, Rural Technology Enterprise, P.O. Box 28201, Nairob Providing all iron parts, specialized in installation of cooker, complete with brick work.
Proposal for improvement: Ash pit 20 x 20 x 60 cm with ventilation system in pit cover place and with water drainage at bottom. This would reduce over-all height of cooker by 10 cm and provide for more ash space.
Fig. 3 Heating, holding and cooling in large scale production of cultured milk
