UHT milk in PET - Milk with a 90 day refrigerated shelf life

Throughout its history, Centrale del Latte di Brescia (Italy) has not interrupted its production for a single day, not even in the turmoil of wartime. Back then, with its own sales fleet the dairy distributed pasteurised milk twice a day in half-litre and litre glass bottles with an aluminium seal closure as an original-packing guarantee.

In 1960, the dairy doubled its production capacities to 100,000 hL and improved its pasteurisation capabilities. Shortly afterwards, it introduced its first triangular cartons as milk packaging and in 1963 was the first Italian firm to install a line for UHT milk.

Figure 1: The PET-Asept line features a BLOC comprising an isolator, a rinser and a filler.

In the '70s, milk packaging was then changed over to rectangular brick cartons, which in the '80s were supplemented by cartons with a square base. The square brick carton was to remain the symbol for pasteurised fresh milk from Centrale del Latte di Brescia until 2001.

Following conversion into a stock corporation in 1996, Centrale del Latte di Brescia began in 1998 to produce and sell ultra-high-temperature organic milk. To ensure the shelf life of its organic milk (and the conventionally produced variety) Centrale del Latte di Brescia sterilises its products by directly injecting steam at 148°C. Steam injection provides quality advantages, explains Technical Director Paolo Bonometti. In contrast to conventional processes featuring heat exchangers, the milk does not come into contact with hot metal, thus avoiding baked-on deposits, caramel taste and colour changes. The temperature can be altered as well. As pre-treatment prior to steam injection, the milk is separated in a centrifuge. This product-friendly UHT sterilisation process is a precursor for further process and packaging innovations.

All a question of the shelf life

It was in 1999 that fresh milk in PET made its debut on the Italian market.

A change in the law helped fresh milk in PET to achieve a further breakthrough. Since 1989, the applicable regulation in Italy had been "Fresh milk has a shelf life of four plus one days". In 2002, an Italian dairy conglomerate attempted to trick its way round this by bottling fresh milk with a shelf life of 15 to 20 days in Germany and then delivering it to Italy. The sector was not enthusiastic, but the government bowed to the pressure and from mid-2003 allowed milk pasteurised at 75°C to be classified as fresh milk with a shelf life of 6 plus 1 days.

The shelf life stated for ESL milk in the refrigeration chain lies in the producer's responsibility, while UHT milk is limited to a shelf life of 90 days by statute law.

Figure 2: Attractive world premiere: UHT milk in PET as full-fat milk (red) and reduced-fat milk (blue).

For fresh milk, PET has already replaced the carton

But even without this assistance, in the fresh milk sector PET succeeded in replacing 90% of carton packaging within three short months from the launch. Centrale del Latte di Brescia simply marketed both packaging variants for a time at the same price and let the consumers decide. Today, fresh milk from Brescia is found only in the PET bottles, thanks to its enormous success among consumers.

The 'UHT in PET' project

The next project, UHT in PET, was already waiting in the wings. This was far more challenging because so far no one had ventured to try it and there was no empirical feedback to rely on. Centrale del Latte di Brescia's technical director Paolo Bonometti and Claudio Zanardini, responsible for technical service, were the pioneers for the groundbreaking project.

"In our opinion, a bottle, whether it's glass, PET or HDPE, is the right packaging for a fresh product," says Paolo Bonometti. "Of course," he concedes, "filling in cartons is relatively inexpensive, not least due to the lesser amount of machinery required." But as packaging for a fresh product he sees a lot of advantages for PET, which compensate for this.

Figure 3: The entire PET-Asept line is accommodated in a minimal space of approximately 100 m².

In comparison to glass, PET is light and robust, amenable to interestingly creative design and recyclable. The costs of glass and PET remain comparable.

When it came to the alternative HDPE, in-house production of the bottles would not have proved as problem free. "Brescia has so far only handled cartons, so the quantum leap to HDPE bottle production, and to a technology that's already regarded as obsolete, would have been too great. Moreover, the machines required for this purpose run at relatively low outputs. We wouldn't have been so flexible. PET is simple. The blow-moulding process is standard, so we can get high levels of productivity." In Bonometti's eyes, PET's gas barrier properties are another bonus. The material is recyclable and if it is incinerated no environmentally harmful emissions are produced.

Figure 4: Able to perform the filling operation without touching the bottle, the Volumetic VODM-PET is ideally suited to aseptic filling processes.

Full-sleeve labelling with metal-coated PET film

The precise definition of the bottle thread has proved highly beneficial as well, providing a hermetic seal. A cone in the closure presses accurately on the thread for a tight seal. Centrale del Latte di Brescia can accordingly dispense with aluminium foil over the opening. To make doubly sure, there's a safety ring at the closure and a specially developed fullsleeve label covering the closure, which Centrale del Latte di Brescia has had patented.

This complete label has another vital function: it improves the barrier properties against UV light and of course also enables the product to be displayed to optimum visual advantage. To protect the opaque surface of the bottle against light Centrale del Latte di Brescia employed a PET film metal-coated with an ultra-thin layer of aluminium, in a thickness of only 100-200. A normal aluminium foil, by contrast, is thicker by three powers of ten. "This means the PET film can also be completely recycled and the energy consumed during metal-coating is of course enormously reduced", is how Bonometti sums up the environmental benefits.

Away from the carton: everything favoured PET

"The starting point was the thought that pretty well everybody in the milk market was offering classical containers in the shape of polylaminated cartons. We wanted something different, something new and practical," explains Bonometti. Because UHT milk in PET constitutes a minor revolution in itself, Centrale del Latte di Brescia, in conjunction with two outside specialist laboratories from the food sector, ran exhaustive checks on the barrier and other properties of PET and possible interactions between milk and PET.

The essential pre-conditions were that the milk in PET was filled aseptically and that the closures were sterilised as well. Centrale del Latte di Brescia compared the same milk, filled once in cartons and once in PET, over a period of four months' storage time at ambient temperature. Analyses were performed every 15 days and in parallel a warm test at 40°C up to 45 days. In order to ensure that there was no difference between the UHT milk in the carton package and that in the PET bottle the acetaldehyde content was measured at regular intervals, the aromatic substances were analysed with a gas chromatograph and HPLC and sensory taste tests conducted.

Figure 5: In the integrated double-channel rinser, the disinfected PET containers are rinsed with peracetic acid and flushed with steam.

The results were persuasive. No differences were discovered in terms of protein and vitamin composition, there was no interaction between PET and milk, the tests at ambient temperature and the warm test produced the same results.

The blind tastings, too, were favourable. The labelled PET bottles scored well in terms of oxygen barrier and pressure stability. The light-permeability for wavelengths of 380-750 mm, at <0.1 %, was significantly below the internationally specified value of <2 %.

To sum up - all the trials, and the market tests as well, indicated that PET was the right option.

Figure 6: With the Krones logo and the slogan "Krones technology and reliability" on the UHT milk bottle, Centrale del Latte di Brescia demonstrates its confidence in Krones' technology.

Filling technology

All that was missing was the appropriate filling technology. The Krones PET-Asept system with isolator technology was recommended not only by the good empirical feedback in terms of microbiology, handling, productivity and reliability. The compact-size construction was an important argument as Brescia had allocated only one hundred square metres for the aseptic line rated at 12,000 containers an hour.

The compact-size PET-Asept line features a BLOC comprising isolator, rinser and filler. In the isolator, the containers are disinfected inside and outside over a defined period with peracetic acid and steam, before being rinsed in the downstream doublechannel rinser.

Volumetric, non-contact filling

At the Volumetic VODM-PET 50-valve filler, the volume of the product being filled can be precisely specified using an inductive flowmeter. Able to perform the filling operation without touching the bottle, the Volumetic VODM-PET is particularly suited to aseptic filling processes. The electronic control system provides for pre-programmed filling steps reproducible at will.

The bottle is led to the filling valve in neck-handling mode. With this filling system, no lift cylinders are required, since filling runs in non-contact mode. The advantage lies in optimised hygiene, combined with a maximised filling angle. As soon as the bottle has been transferred to the filler, the electro-pneumatic control system opens the filling valve, thus triggering the filling operation.

Figure 7: PET containers for UHT milk.

In line with the dairy industry's stringent hygiene regulations, the VODM-PET design features a greatly reduced number of functional parts and is concomitantly easy to clean. Automatic CIP cups support the cleaning function.

The isolator technology is conditional on sterilisation of all the components located inside it and of the inflowing media and the packaging components being fed in. The closures are therefore disinfected separately in a bath of peracetic acid.

Swiftly installed and validated

Installation of the line began in January 2004. This also included the entire peripherals, with the chemical store, the dosing systems, the steam and sterile air supply. By May 2004, an external test laboratory had already validated the aseptic process. At the end of June 2004, the test market was inaugurated, starting outside the core market of Brescia itself.

At the same time, a project was launched to place the existing Contiform Compact 6 in one room with the new Contiform S8, thus easing the constraints imposed by the confined space available. "Krones handled the whole project with intense commitment and excellent support, both in the installation phase and during the validation process," concur Paolo Bonometti and Claudio Zanardini.

Centrale del Latte di Brescia decided to blow-mould the bottles as white-opaque containers, so that the base, not covered by the label, is opaque as well. The dairy offers UHT milk in PET bottles in the three variants: full-fat milk (red sleeve label), reduced-fat milk (blue) and skimmed milk (green), packed in 6-, 8- and 12-bottle packs.

Operational success

For Centrale del Latte di Brescia, the success of UHT milk in PET is very important. Not only are the expectations throughout the entire dairy industry very high (much to Bonometti's disquiet), consumers in the Brescia region (in contrast to the rest of Italy, where about three-quarters of milk consumption is still accounted for by fresh milk), got used to UHT milk very early. The proportion of UHT milk is concomitantly higher, at about 50% of output.

As with the fresh milk, PET bottles containing UHT milk will at first be on the shelves together with milk cartons and will be offered at the same price. But in view of the extreme visual appeal of the UHT PET bottle alone, consumers in and around Brescia are expected to soon be saying farewell to UHT milk in cartons since they cannot be reclosed properly and cannot be recycled either.

Krones equipment is distributed in Australia by JL Lennard Pty Ltd and in New Zealand by KSL Packaging Ltd.