Shelf-stable milk: conscientious convenience
15 Feb 2021
In the 1960s, a milk processing technique using ultra-high temperature (UHT) combined with packaging and filling innovations resulted in a product that solved the age-old challenge of significantly extending the shelf life of liquid milk. Over the decades, UHT milk processing technologies have improved – as have the products – giving consumers around the world a convenient, tasty and nutritious liquid dairy milk option.
According to Euromonitor International, around 34 percent of liquid milk consumption today is shelf-stable or UHT milk. The top three regions for consumption are Western Europe, followed by Latin America and Asia Pacific. In terms of growth markets, the story is slightly different: Retail volumes are dipping in North America and Western Europe, whereas in Asia Pacific, Australia, Eastern Europe, Latin America, the Middle East and Africa, consumption of UHT milk is on the rise. For countries that import a lot of milk, UHT delivers a clear benefit by maintaining a long shelf life under ambient conditions – anywhere from six to nine months.
We spoke with Ludger Tacke, Head of Product Engineering Management - Hygienic Processing at GEA, to find out more about the UHT milk process and what trends, conceptions – and even misconceptions – are shaping this important milk category.
How does UHT milk differ from other kinds of milk consumers can buy?
LT: Many people only differentiate milk by its fat content however, it can also be processed in different ways, resulting in four basic types of milk:
- raw fresh milk
- pasteurized milk
- extended shelf-life milk (ESL)
- ultra-pasteurized or ultra-high temperature milk (UHT)
Raw fresh milk undergoes very little processing between the dairy farmer and the consumer. Some people prefer the taste and full nutritional value that raw fresh milk provides, buying direct from farmers. In many countries it not allowed to sell raw milk in stores as consumer safety cannot be guaranteed. Because it is not heat treated, raw milk retains its pathogens and therefore has a relatively short shelf life – normally seven to 10 days.
Pasteurized milk is heated from 72 to 75 degrees Celsius for a duration of 15 to 30 seconds. This process is sometimes referred to as high temperature/short time (HTST) pasteurization and as a result, about 99.9 percent of the pathogens are inactivated. The milk is then cooled and from thereon must be refrigerated given that any remaining bacteria can grow and multiply otherwise. Pasteurized milk has a shelf life of roughly 12 to 20 days from the time of packaging.
Another option is ESL or extended shelf-life milk, which must be refrigerated after packaging and has a shelf life between 21 and 45 days. This is achieved by removing or inactivating the bacteria in the milk before bottling. Removal can either be done mechanically with bacteria-removing clarifiers or microfiltration, or by using ultra-pasteurization at a temperature of around 127 C for four seconds to inactivate the bacteria. Alternatively, these methods can also be combined.
Ultra-pasteurized or UHT milk is heated to at least 138 C for two to four seconds, inactivating all bacteria; it is then sterile. To guarantee product stability, high-pressure homogenization is often used, followed by heat treatment to ensure product stability. The milk is then filled aseptically – in air-proof, light-proof and sterile containers. UHT milk does not require refrigeration until it is opened – up to which time it enjoys a shelf life of six to nine months when kept at ambient temperatures of between 20 to 30 C.
Over-supply is a real challenge and can lead to operators having to dump large quantities of milk. When this happens, it’s not just the milk that is wasted – you also lose all the inputs that went into its production which includes feed, water, medicine, farm labor and machine costs.”- Ludger Tacke, Head of Product Engineering Management - Hygienic Processing, GEA
- Ludger Tacke, Head of Product Engineering Management - Hygienic Processing, GEA
What role can UHT milk play in reducing food waste and the environmental footprint of dairy?
LT: Farmers and dairy processors frequently struggle with fluctuations in supply and demand. Over-supply is a real challenge and often means operators must dump milk. When this happens, it’s not just the milk that is wasted – you also lose all the inputs that went into making that milk which includes feed, water, medicine, farm labor, machine costs, etc. Many people around the world face food shortages or malnutrition, which makes throwing away milk an even greater travesty.
This situation could be eased if more raw milk was processed using UHT, given that once processed and packaged, it can be stored under ambient temperatures for several months. In this time, milk demand could pick up, or another market found. In a nutshell, UHT milk can provide greater stability in an industry that is often fraught with instability. As is well-known, the same strategy can be used with nutritional formula, such as powdered milk for infants, which also has a much longer shelf life than other types of pasteurized liquid dairy products. Milk powder can also be used to produce UHT milk, again lengthening the shelf-life of milk.
Because shelf-stable milk does not require refrigeration until opened, this translates into reduced cooling costs and emissions all along the supply chain. And not having to repeatedly throw away unsold milk that has passed its sell-by date is an important benefit to retailers, who generally have tight margins. And of course, this also reduces waste. Oddly enough, nearly all organic milk in the U.S. is UHT, yet still kept in coolers because consumers have concerns about buying warm milk. This even extends to some soy-milk products from manufacturers who pay U.S. supermarkets extra to have their shelf-stable products sold in the refrigerated section. Of course, this is unnecessary and will hopefully change with greater awareness and focus on the environment.
Milk is a staple in many households. The option to have more on hand without worrying it will go off before it is consumed is a major plus for busy families – and this also reduces food waste. If you buy multiple cartons, they don’t have to take up precious space in the refrigerator. In countries lacking end-to-end cold chain networks, UHT milk is a nutritional lifeline. As the world becomes more urbanized, fewer people have access to fresh milk making UHT a logical and practical choice – and one that comes with a reduced environmental impact given less refrigeration (i.e., energy) is required.
As we have seen all too recently, having access to non-perishable foods isn’t merely a luxury, it’s an absolute necessity.”- Ludger Tacke, Head of Product Engineering Management - Hygienic Processing, GEA
- Ludger Tacke, Head of Product Engineering Management - Hygienic Processing, GEA
UHT milk seems to have a: “you either love it or you hate it” reputation. Why is that and what factors contribute to this?
LT: Well, food and taste are extremely personal and tend to be heavily influenced by our culture and experiences; perception also plays a major role.
It is true that UHT milk tastes different or at least slightly different than pasteurized milk. Some describe UHT milk as having a slight caramelized or sweet taste. The extent depends on the processing method used, but this is due to the heating process, which inactivates microbes and the enzymes that spoil milk. But if overdone, this can result in a burned flavor. The use of heat does change the properties of milk. However, this is minimized with modern UHT technology which uses a short and precise heating process.
In terms of nutrition, UHT milk has the same caloric and calcium amounts as raw milk. However, there will be slightly less folic acid, vitamin B12, vitamin C, thiamin and iodine, which is also true of pasteurized milk. These losses are typically kept to below 20 percent and can be offset by the re-addition of vitamins.
For people who dislike drinking warm milk, you just need to put it in the refrigerator an hour or two ahead of using it. As mentioned, in the U.S., where UHT has met resistance, many people are now consuming it without even knowing it because nearly all organic milk there is UHT treated to accommodate longer transport times. And of course, there are numerous examples of people who have moved to other countries where UHT is the most common milk available, adapted to it, and were quickly won over by it.
What technologies and solutions does GEA offer for UHT milk processing?
LT: GEA has more than 125 years of liquid dairy processing experience and nearly a century of farming credentials. We understand milk. Our UHT milk processing know-how and product portfolio span every stage, from milk and ingredients reception, milk separation, treatment and homogenization, through to filling. Most of these steps are managed via GEA automation and process control solutions. We’re able to take care of every detail, including the configuration of robust, long-lifespan valves and space-saving, hygienic pipework, and can accommodate batch or continuous processing.
Our inline UHT process solutions integrate separation, standardization and the aseptic process treatment, which reduces fixed and variable costs, especially for energy consumption. Fewer components mean less water and detergent are required; improved product quality is also ensured, including better flavor, less dissolved oxygen, and optimum shelf life. Our customers can choose from three different UHT plant types, which include options for either direct or indirect heating – which we tailor to match their product and process requirements, plant layout and throughput. We also offer customers the opportunity to test processes with our UHT pilot plants, either in a GEA test facility or at the customer’s production site.
Adding homogenization to the process improves the stability of the milk by reducing the size of fat globules. Homogenization helps prevent the cream from rising to the surface or from adhering to the sides of the container, improving mouthfeel, shelf life and overall milk quality. While homogenization can take place before or after heating, depending on the heat process used, its use after heating confers the best results. Doing so prevents protein aggregation and discourages the formation of sediment from heat-precipitated proteins. Our extensive range of GEA industrial homogenizers enjoys a market-leading position among dairies given their reputation for superior quality and efficiency.
Following processing, UHT milk requires aseptic filling. GEA Aseptic Blow Fill System ABF ensures sterile conditions with high reliability and performance. In this process, the preforms are sterilized and then blown with sterile air in a sterile environment, with sterility maintained throughout the filling and capping process. This method minimizes the use of chemicals, eliminates the need for bottle rinsing, allows for a simpler and smaller layout while reducing energy consumption. Our Whitebloc Filling System Aseptic is specifically designed for the dairy industry and for use with PET and HDPE bottles. We also offer wet sterilization options with our ECOspin2 Zero and Modulbloc systems.
What are the advantages of PET bottling?
LT: PET provides the optimal packaging material for liquid dairy and is significantly growing in this market thanks to the fact that it is 100 percent recyclable. It provides excellent barrier properties necessary for meeting the food safety requirements for sensitive beverages.
For consumers, PET containers are easy to use, particularly when it comes to opening and pouring. And they are easy for consumers to rinse and recycle, which cannot be said of all UHT milk packaging types.
What other trends support increased demand in UHT milk?
LT: Well, certainly e-commerce and increased urbanization, which means that food and beverages might be in transit longer and without refrigeration. In dense urban areas, consumers picking up their own foodstuffs are more likely to be on foot, in public transportation, on a bike or scooter to transport their groceries, which could be problematic for sensitive foods, like dairy products.
Also, as more people migrate to cities and move away from an agrarian lifestyle, packaged and long shelf-life products become more essential. The general demand for convenience seen in the beverage industry will likely drive up the number of UHT milk drinkers; also, it tends to be less expensive than fresh or pasteurized milk. Once people switch to UHT milk, it seems they rarely switch back. And although I certainly hope this does not happen, increasing climatic temperatures could make fresh and pasteurized milk a less practical option for consumers in some parts of the world. And as we have seen all too recently with the COVID-19 restrictions, having access to non-perishable foods isn’t merely a luxury, it’s an absolute necessity.
