As more dairies consider adding extended shelf-life (ESL) milk to their portfolios, many are also discovering that getting started with ESL production can be anything but straightforward. Based on insights from experienced Tetra Pak milk processing experts1, we’ve put together a guide for what you should think about, if you’re thinking about making the switch.
Growing interest in ESL milk is creating new business opportunities for dairies around the globe. But new opportunities often mean new challenges, and ESL is no exception. For most dairies, setting up their first ESL production line will entail a whole host of considerations they have not encountered before, and that can be true whether you’re coming from traditional pasteurized milk processing or if you work with ambient UHT products.
How can you avoid potential pitfalls and maximise your chances for a successful ESL product launch? There are four key questions to ask as you get started:
In ESL processing, there’s no such thing as a one-size-fits-all solution. Profitable production depends on having a line that is designed as specifically as possible to fit your requirements. As a result, your starting point must focus on the types of products you plan to produce.
Much of this step comes down to defining what product quality means for consumers in your market. What’s important from a sensory perspective? What is the taste and mouthfeel that your consumers are looking for? The answers to these questions are critical for identifying your technical requirements later on.
For example, in markets where traditional pasteurized dairy is dominant, consumers may be used to a “fresher” milk flavour profile – and will come to expect this from chilled ESL products as well. Contrast this to places where ambient distribution is the standard, and people associate milk with the “cooked” taste and rich, creamy texture of UHT dairy. Such subtle, but important differences are the reason you cannot simply copy an ESL line design from a different market and hope for success.
Just as there is no universal ESL solution, there is no universal definition of “extended shelf life.” In other words, developing an ESL product is not about hitting a specific target of days, but rather discovering how far you can extend the shelf life of chilled products, with traditional pasteurization as the baseline. You therefore need to consider not only the technologies you will require, but also the factors that will limit your efforts.
Part of the challenge here is understanding just what you mean by “shelf life” – a notoriously tricky metric to define2. Generally speaking, this is a measurement of the milk’s microbiological load over time. There are, however, a number of variables that can influence how long it will take for microbial growth to either cause spoilage or surpass the defined acceptable limit of total plate count in the milk.
The first of these is the quality of the raw milk you use, and how that milk is handled between the farm and your processing plant. Some dairies have the benefit of close farmer relationships, and can control this part of the value chain to ensure that only premium grade milk is used for their products. Others, however, may only have access to whatever is available on the open market at any given time. Ultimately, this plays a big role in determining what you can achieve: the higher the quality you have as a starting point, the more you will get out of treatment, and the longer you will be able to extend shelf life.
The distribution conditions in your market also have a big impact. Again, this is a question of control, as keeping milk at lower temperatures after processing slows microbial growth. Dairies that can ensure 8°C or below at every step between the plant and the consumer will have a better chance at providing a longer shelf life. A less established and less stable cold chain, conversely, will limit shelf life. Where low-temperature distribution is particularly unreliable, it may be impossible to even offer a chilled ESL product.
Once you have identified your quality goals and potential limitations, it is easier to choose the right processing approach for your needs. There are two ways to minimise the microbiological load: either you can remove microbes from the milk, or you can kill them.
Microfiltration
When it comes to removal of microorganisms, microfiltration technology represents the most efficient solution. The bacteria and spores in question, while microscopic, are ever-so-slightly larger than the desired components of the skim milk. The right filter design can therefore capture microbes and rinse them away, while allowing the “clean” skim milk to pass freely into downstream processing.
There are a number of reasons to consider microfiltration, but the main one is the sensory profile. Unlike high-heat treatment used to kill the spores, filtering them out provides a product that resembles pasteurized white milk in both taste and mouthfeel. This can be ideal in markets where milk drinkers are used to a traditional chilled product.
Certain regulatory requirements can also necessitate the use of microfiltration. For example, existing law in some countries requires products sold as chilled “fresh” milk to test positive for peroxidase. As these enzymes cannot survive the high-heat treatment process, bacterial removal is the only alternative for ESL production when such rules are in place.
High-heat treatment
As noted, the method for killing spoilage-causing bacteria is high-heat treatment (HHT). HHT offers more efficient reduction of the microbiological load than microfiltration technologies. In other words, it can enable significantly longer shelf, or it can be used to account for limitations in raw milk quality or cold chain stability. This approach may therefore be suitable to markets where maximising chilled shelf life takes priority over providing a traditional “fresh” milk taste.
Both direct and indirect HHT can be used successfully for ESL milk production. Direct heat treatment allows for a minimised heat load, which makes this the typical choice when sensory characteristics of the end product are a top priority. Indirect heating systems can also be optimised for ESL production, and will provide lower utility use for reduced operating costs and a lower environmental impact than direct solutions, albeit with a different flavour profile.
Flexibility is one reason that some dairies choose HHT. Microfiltration can only be used for ESL white milk, but HHT offers opportunities for a wider range of products, such as ESL flavoured and formulated milks and ESL cream. With HHT, it’s also possible to produce chilled ESL and ambient UHT products on the same line.
While local regulation can prohibit HHT, the reverse is also true. Certain jurisdictions have rules in place limiting what can and cannot be manually removed from milk during processing (e.g., retentate). In these places, HHT may be the only option for ESL production.
Identifying the right treatment solution for your products is an important step, but you would be mistaken in thinking that successful ESL processing begins and ends at the choice of microfiltration or HHT. This is just one of many decisions you will need to consider.
Your choice of treatment solution will help you to address this first challenge, but that still leaves two big areas to focus on in the rest of your plant. Preventing recontamination will require hygienic line designs for both processing and downstream, as well as in the handling of packaging materials and your filling line. To meet the shelf life stamped on the package, you will also need to ensure the milk is kept at or below 8°C at all of these steps, as well as throughout logistics and distribution – as much as you can control.
In other words, extending chilled shelf life is an incredibly complex undertaking, with numerous, overlapping variables to consider. It puts high demands on you as a dairy processer, but also on your choice of process solution supplier. Close collaboration with a partner that can offer a 360-degree perspective of the dairy value chain – and support every step of your production – is the surest way to produce the types of products you want, with the best possible shelf life.
Get the most from your ESL processing
Looking for the right technology to grow your portfolio and support long-term product innovation? Learn how we at Tetra Pak can work with you to design a flexible line, optimised according to your needs, that supports product quality and shelf-life goals for all your ESL products – and beyond.
1 Unless otherwise noted, all content in this article is based on an in-depth interview with Carin Cronström, a Line Solution Manager at Tetra Pak with extensive experience supporting customers in developing solutions for ESL processing. To learn more about any of the information featured here, please contact us.
2 For a deep dive into the various methods for defining and measuring dairy shelf life, please download our ESL white paper.