Flash pasteurisation

Some manufacturers produce RTD products at drinking strength but this is wasteful of plant and requires large-volume production tanks. The usual approach is to manufacture a syrup or concentrated form of the beverage that is then diluted with carbonated water. The syrup, which can be flash-pasteurised, can be dosed into bottles that are then topped up with carbonated water. This is known as the post-mix method. Where the alternative, pre-mix , method is employed, syrup and water are mixed in the correct proportions in special equipment prior to bottle filling. 

Most concentrated beverages contain fruit juice or whole fruit , a term that refers to a comminuted form of citius that includes components of juice, essential oil, peel (flavedo) and pith (albedo). Concentrated soft drinks are usually flash-pasteurised and chemically preserved. Their dilutable form means that they are often held in partially filled bottles for significant lengths of time (often many weeks or even months) and are extremely vulnerable to spoilage by micro-organisms. 

Concentrates are normally produced at their packed strength, flash-pasteurised and transferred immediately to their final packaging. 

The main drawback in the use of fumaric acid is its slow solubility rate in compar ison with citric acid, and special methods need to be employed in its dissolution. It has been claimed that fumaric acid and its salts have a tendency to stabilise the suspended matter in both flash-pasteurised and frozen fruit concentrates (McColloch Gentile, 1958). 

The manufacture of dilutables is essentially a very simple process, with the required ingredients being mixed in order in a large vessel. After checking the final volume for process variables the mixture is then flash pasteurised and filled into the required containers. 

To avoid such microbial problems manufacturers must either employ aseptic packing lines, which are very capital-intensive, or use flash pasteurisation and scrupulous downstream hygiene and close control over formulations. 

Typical flash pasteurisation operations for fruit juices and nectars will employ a plate pasteuriser with heat recovery and final product cooling. Typical flash pasteurisation conditions will use temperatures between 85 and 95°C with holding times varying between 15 and 60 s. Selection of the appropriate conditions will depend on the product, including the level of microbial load pre-pasteurising. If enzyme deactivation is required as well as microbial removal then a temperature between 90 and 95°C will normally be used. At these temperatures, holding times are normally reduced to around 15 s. 

For aseptic packaging operations, flash pasteurisers are often linked integrally with the aseptic packaging unit, either directly or via an aseptic buffer tank. When flash pasteurisation is used, care should be taken to minimise product recirculation when the pasteuriser is in divert mode. Excessive recirculation can lead to thermal damage to the product, resulting in unpleasant cooked flavours and product browning. 

If products are filled cold into clean bottles on clean (but not aseptic) fillers, stored in refrigerated warehouses and sold to the customer from chill cabinets then quite long shelf lives can be obtained. The product is generally flash pasteurised to ensure its cleanliness prior to filling. 

Even at this low alcohol level microbiological spoilage is a hazard. Suggested manufacturing processes are benzoic acid preservation with either sterile filtration or flash-pasteurisation of the syrup, or in-pack pasteurisation. 

Section V Stabilising Agents Recommended none are recommended Tolerated citric, tartaric, malic, ascorbic, fiimaric acids from nonsynthetic sources according to BATF standards. Low temperatures for tartrate stabilisation (cold stabilisation). Flash pasteurisation with technical justification Prohibited potassium ferrocyanide, synthetic citric acid, metatartaric acid, sorbic acid and sorbates... 

Two main methods are used to pasteurise beer tunnel pasteurisation, where bottles or cans are passed through a series of water jets applying heat, and flash pasteurisation, where the beer is heated rapidly in a plate heat exchanger and holding mbe before packaging. 

In flash pasteurisation the beer is rapidly heated in a plate heat exchanger and held in holding tubes where the required number of PUs is applied in a matter of seconds. Typically the beer will be heated to around 72.5 °C and held for 20 s, which will give 20 PUs (Figure 12.2). 

As flash pasteurised beer is not pasteurised inside a sealed container a higher degree of hygiene and sterility is required than for tunnel pasteurisation. It is particularly critical once the beer has left the pasteuriser, and the buffer tank, filling equipment and all... 

Figure 12.2 Flash pasteuriser heating section, cooling section, regenerative section.

The short time that flash pasteurisation takes means that maintaining the correct temperature and holding time is critical. 

Flash pasteurisers work best at a constant flow rate but packaging operations mean that this is not always possible and pasteurisers will need to be able to work at variable speeds. It is usual to have an outlet buffer tank to smooth out the flow rate prior to tilling (Dunn, 2006). 

Another potential problem with flash pasteurisers is that of plate failure, when corrosion causes a hole to develop. This can allow unpasteurised beer or coolant to leak into the pasteurised beer. A good maintenance programme will minimise occurrence. Also a booster pump is typically used to ensure pasteurised beer is maintained at the highest pressure in the system (at least 0.5 bar higher than the product) so that in the event of any leakage it will be of pasteurised beer into unpasteurised beer or coolant, ensuring that product is not contaminated (Hyde, 2001). 

Verification of the process will need to be based on likely errors that may occur and the organisms that are most likely to cause problems. The different processes employed in tunnel pasteurisation and flash pasteurisation mean they have different potential problems and monitoring must take this into account. For example, blocked jets or gas breakout are specific to particular methods though poor maintenance or calibration can apply to both. 

As breweries strive to reduce their water and energy usage the trend has been to move away from mnnel pasteurisation to flash pasteurisation. It has been estimated that the costs of flash pasteurisation are only 15% of that of tunnel pasteurisation... 

S Reduced pasteurisation. At present, pasteurisation is the preferred means for destroying spoilage bacteria, in particular, lactobacilli. Tunnel pasteurisation is employed for cans and glass and flash pasteurisation for beers destined for kegs or polyethylene terephthalate (PET) bottles. It is essential that both excessive and insufficient filtration is... 

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