Farming has been a very popular agricultural activity in South Africa, providing income for small scale farmers and jobs to thousands of people. Over the past few years, there has been an increase in the demand for animal products such as meat and milk, and the dairy industry has been meeting this demand. The intake of unprocessed milk in South Africa increased by 4.8% in 2018 compared with 2017, and this increase was attributed to various factors such as a reduction in prices of unprocessed milk, higher feed costs and varying weather conditions in certain areas in South Africa.

The South African secondary dairy industry consists of a few large processors operating nationally, a growing number of processors who operate in more than one region, a large number of smaller processors who operate in specific areas, and several milk producers who sell their own produce to retailers and consumers – known as producer-distributors (PDs). The number of PDs decreased by 60% from January 2009 to March 2019, and milk processors decreased by 32% over the same period. In South Africa, 98% of the milk produced is sold formally to commercial processors, which are different from the situation in most other African countries where milk is mostly sold to smaller processors.  In 2018, the South African dairy market was divided into 62% liquid and 38% concentrate products.

Pasteurised liquid milk and ultra-high temperature (UHT) milk are the major liquid products, while hard cheese is the major concentrated product.

The increase in milk production over the past few years can be attributed to an increase in the demand for fresh milk and ±20% for milk products such as soft cheeses and flavoured milk. And with the development and introduction of various other milk products, this demand will continue. Milk is highly nutritious and an important part of the human diet, especially essential for growing children and as a result there is always a demand and pressure to maintain a continuous supply.

There is a demand by consumers for processed milk to have a taste profile like that of unprocessed milk, while keeping its extended shelf life properties.  Consequently, there has been an increased variety of milk products using various processing techniques to achieve safe products with stable shelf life attributes. Some of these techniques include Ultra High Temperature (UHT) milk and Extended shelf life (ESL) milk.

Raw milk is considered very desirable in parts of the country. However, raw milk poses many possible safety hazards, such as a susceptibility to bacterial contamination. To provide consumers with product diversity and convenience, technological improvements in milk production have been made mostly in unit operations such as separation, standardisation, pasteurisation, homogenisation and packaging. These improvements have been possible through research and knowledge of the functional properties of the different ingredients and components of milk and the effect they will have on the structure and texture of the final product. Apart from extending the shelf life of milk, other improvements have been made in the continuously evolving dairy industry; standardisation of milk has become faster and automated to receive results of milk analysis faster and methods of adjusting the milk to the required fat content.

Why do some dairy products have longer shelf-life than others?

The dairy industry employs technologies aimed at extending product shelf life. Some commonly used methods include heat treatment of fluid milk products for a pre-determined time and temperature; acidification by the addition of starter culture in the case of cultured dairy products such as yoghurt, or buttermilk; the drying of milk concentrate to produce milk or skim milk powder; the addition of preserving agents such emulsifying salts in shelf-stable processed cheeses. Shelf-life of fluid milk products, for instance, is dependent on various factors, namely heat treatment, quality of the incoming raw milk, additional processes such as micro-filtration, filling conditions, temperature control and packaging technologies. However, heat treatment remains the primary factor that determines the shelf-life.

Heat treatment is the most widely used processing technology in the dairy industry. Its main purpose is to destroy microorganisms, both pathogenic and spoilage, to ensure the milk is safe and has a reasonable shelf-life.

High-temperature short time (HTST) pasteurisation increases the shelf life of milk to 10-14 days when refrigerated, HTST milk is processed at 72 ⁰C for 15s. Another process used to increase the shelf life of milk further is Ultra-high temperature (UHT) processing, UHT milk was introduced to form a product with a longer shelf life than HTST milk, it has a shelf life of 9 months at ambient temperature and is processed at 135-140 ⁰C for 1-2s by using either direct heating, steam injection or infusion. UHT milk can accommodate households with limited or inadequate refrigeration.

The consequences of using high heat during processing do become problematic, with the main problem with HTST being that consumers still wanted a product with a longer shelf life than what is provided, and with UHT milk it was the undesirable thermally derived changes to the product such as cooked or caramelised flavours caused by Maillard browning reactions between sugars and proteins in the milk, which may also cause a slight browning of the milk owing to the increased temperature during processing, and combined with undesirable off-flavours and other flavour limitations. To meet consumer demands and keep consumer satisfaction for milk that has a longer shelf life than raw milk but still has a taste as close as possible to fresh milk, Extended Shelf-life Milk (ESL) milk was introduced, which has a shelf life of 21-28 days at 7 ⁰C. Several factors affect the shelf life of milk; the quality of raw milk used, its transportation, processing and storage conditions being a few.

What about food safety management, what is the dairy industry doing?

Historically, the dairy industry has been involved in the supply of safe products to consumers. New technologies have always been followed worldwide to achieve this objective. Continuing to monitor the evolution of food law, regulations, analytical methods and quantitative risk and exposure assessment techniques, the industry will continue to implement this risk-based food safety management approach. It allows all aspects of a food safety system, from the farm-to-fork (raw material, food processing consumer behaviour), to be taken into account, rather than separating responsibility for any particular component of the chain.

References
Risk-Based Food Safety Management IDF Factsheet – December 2014
Shelf life of Dairy Products IDF Factsheet – February 2012
Lactodata vol 23 no 1 May 2020

This opinion piece by:

Elna M. Buys
Professor and Head of Department of Consumer and Food Sciences
Faculty of Natural and Agricultural Sciences, University of Pretoria