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In for the long run

Tetra Pak recently published a white paper on how new assessment methodologies can allow extended running times for milk pasteurizers. Andrzej Holanowski, senior dairy technologist at Tetra Pak, discussed how this works with Dairy Industries International.

What is the most obvious benefit of extending the running times of milk pasteurizers?

From a dairy plant management perspective, it is desirable that running times of processing equipment are maximised to optimize plant efficiency, which in turn keeps operating costs down. Our customers can extend the amount of time during which a plant can output consumable products, while maintaining crucial food quality and safety.

For dairies producing large volumes of pasteurized milk, running one Cleaning in Place (CIP) instead of two means saving about 50 per cent of the cost of CIP per milk pasteurizer per day. Furthermore, the longer running times and reduced number of CIPs may have additional beneficial effects on equipment investment, maintenance costs, production shift management and other key parameters.

The specific benefits of eliminating one CIP cycle per day and line include:

  • Reduced CIP cost by approximately 50 per cent (electricity, media, detergents for the specific pasteurizer)
  • Increased processing availability by 2-4 hours per day
  • Possibility to finish daily production circle within 24 hours, e.g. 20 hours processing + 3 hours CIP + 1 hour preparation time

What was behind the research?

For years, the dairy industry has been looking into possibilities for extending production periods of milk pasteurisers. These typically work at 72-75°C with product holding time of 15-30 seconds and would achieve six to 10 hours of processing time before cleaning was required. The demand for going beyond that limit has been the main motivation for undertaking industrial-scale research on optimising pasteurization running time.

When Tetra Pak decided to investigate possibility for new solutions in 2011, it took over a year to complete the research and several more months to transform it into a white paper for the industry.

What was seen as a barrier to extending the running time? Why has this changed?

Historically, the main limitation for the running time of milk pasteurizers was set by the cheese and powder industries. It has been known for a long time that milk pasteurizers, which effectively kill lots of microorganisms in specific circumstances can also contribute to the growth of some types of thermoduric thermophilic bacteria, which can then be released into a heat-treated product. It takes about six to ten hours before such bacteria in pasteurized milk start to exceed quality specific requirements. It is important to note that these additional bacteria are not harmful to consumers, but may influence the quality of cheese and milk powders.

When we looked closer at requirements of the consumption milk producers, we realised that this segment of the dairy industry does not need to be limited by the same requirements as cheese and powder. We gained this insight by taking a different approach to assessing which kinds of bacteria are important for consumption pasteurized milk. Firstly, this group of products is distributed in very low temperatures of 4º to 8ºC. In such conditions, thermoduric thermophilic bacteria coming from pasteurizers have neither the ability to grow further or influence product quality. Typically, these bacteria are not enumerated when assessing pasteurized milk by total bacteria count incubated at 30ºC. This means that it is possible to allow milk pasteurizers to run for longer without requiring cleaning, which disrupts production and reduces run time.

The effect of extending the production run time of a typical milk pasteurizer was assessed on an industrial scale in a pasteurized consumption milk dairy plant. In those tests, we measured the following:

  • Total plate count (TPC) of the raw milk
  • Thermoduric count of the raw milk
  • Plate count of pasteurized milk on TPC agar from the same sample incubated at 30, 37 and 55°C for 72 hours

Our experimental results showed that consumption milk can be run for 18 to 22 hours, with no risk to food safety and quality. The mesophilic plate count in pasteurized milk stayed unchanged during all tests extending to 18 hours.

Taking into consideration our results, we propose that it is possible to differentiate pasteurization line running times, based on different product requirements, with regard to critical microorganisms. Limiting thermoduric thermophilic bacteria are critical for cheese and powder quality but not significant for consumption milk. As such, approximately eight hours’ running time is still appropriate for cheese and milk powder products to limit such growth to an acceptable level.

How big is the consumption milk market, and where do you see this information being used most, geographically?

Global consumption of white milk amounted to 222.9 billion litres in 2016. There was a compound annual growth rate (CAGR) of +1.3 per cent between 2013 – 2016 while between 2016 – 2019 it is forecast to reach 1.7 per cent. This growth is mostly attributable to the developing markets, as opposed to developed markets where white milk has been prevalent for decades. Elsewhere, drinking yogurt has already experienced exciting growth and is forecast to continue with CAGR of 5.4 per cent through 2019. (Source: Tetra Pak Compass)

Pasteurized milk is preferred by consumers in many regions like in Scandinavia, the UK, US, Canada, Australia and New Zealand. In Central and Eastern Europe, it still makes up an important part of dairy supplies to consumers, and even in warmer regions around the world where cold distribution of pasteurised milk is possible. There are many producers catering domestic markets and many more producers using pasteurizers for pre-treatment of milk for UHT processing. All of them can benefit from extending running time.

What about other types of products, such as yogurt?

Yogurt milk is prepared in two steps. First, it is pasteurized and fat standardised. In the second step, it is fortified with different dry ingredients and pasteurized again, this time at 95°C. The first step of the process may benefit from the new approach, whereas the second step will still be limited by fouling of the heat exchangers, which is typical for this elevated temperature. In general, all pre-treatment applications (excluding cheese and powder) which utilise pasteurization at approximately 75°C and therefore need to process during a long time, may benefit from this new approach.

Tetra Pak will soon publish a new white paper with the title “Consumption milk pasteurizers can be run much longer than 8 hours”, in which we describe in much more detail how the new assessment methodology allows extended running time for milk pasteurizers. I would like to encourage all those interested to look for it, and welcome you to share comments on Tetra Pak social media channels.

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