The Pasteurisation Unit (PU) is defined as relating to the sterilising effect observed when Redpost produces PU Monitoring equipment for tunnel pasteurisers and therefore the rest of these science pages focus exclusively on the tunnel pasteurisation of bottled and canned beverages. However, as with flash pasteurisation there is a risk This method has the advantage of having minimal impact on flavour. Mentioned only for completeness this is an alternative to pasteurisation that uses advanced filters to remove sufficient microbiological contamination toĮxtend the shelf life of the product. Cannot process more than one product without downtime.Cannot be used for pulpy products such as Orange juice.No possibility to independently monitor the PUs achieved.Difficult to retrofit into an existing bottling/canning line.Expensive to set up and maintain a sterile environment.Often when flash pasteurisation is usedįor bottled or canned beer, tunnel pasteurisation is used as a secondary process for export beer in order to prolong the shelf life. If hygiene standards are not rigorously enforced.įlash pasteurisation is often used for the pasteurisation of bulk products such as keg beer and milk. Itself is relatively compact and takes up much less room that a tunnel pasteuriser.įlash pasteurisation must be used in conjunction with sterile fill technology and therefore has the risk of post-pasteurisation contamination Heat exchangers to quickly bring the product up to temperature, hold it for 25-30 seconds, then cool the product back down to near ambient. With flash pasteurisation, product is forced through a stack of corrugated plates the plates act as Sterile fill technology became practical. This was when the extreme standards of hygiene required for Can use a lot of energy if improperly controlledĪlthough proposed during the 1800s, commercial flash pasteurisation only took off seriously in the 20th Century.However, solutions are available with double deck designs to optimise the use of space. Heated, tunnel pasteurisers can be extremely large. Due to the length of time the bottles must be A run through the pasteuriser takes between 20-50 minutes at temperatures from 60☌ to 90☌. , then the water is heated externally and sprayed onto the bottles within the pasteurising zones, before being cooled by spraying onto the cold bottles in Water is normally recirculated to improve energy efficiency water is preheated by spraying onto hot bottles within the cooling zones Sophisticated control systems to manage the temperatures, deal with line hold-ups and slow-downs in a way to prevent over or under pasteurisation Keep them at a specified holding temperature and then bring them back down to room temperature. The tunnel is divided into many temperature zones to slowly bring the product up to temperature, The bottles or cans move through the pasteuriser slowly on either a walking beam or conveyor belt. Water is sprayed down on to the packages. The tunnel has a low ceiling with spray heads at regular intervals. Then funnelled into the pasteuriser 'tunnel' before any labelling is added. In the above case the Z-value appears to be approximately 8☌.In tunnel pasteurisation bottles or cans are filled and closed in the normal way, From this line, determine the number of degrees required to change the D-value by one factor of 10 (see Figure 2 below).įigure 2, Calculating a Z-value graphically. Plot at least 3 D-value/temperature pairs on a semi-logarithmic graph and, using your best judgement, draw a straight line through the points that most closely fits the data. How do I determine a Z-value graphically?Ĭalculating a Z-value graphically is relatively easy. A line-of-best-fit is a statistically correct method of representing the data points. In reality however, D-values will not decrease perfectly due to natural variations and experimental error. In a perfect world, the D-value of a particular spore will decrease exponentially as temperature is increased. Since D-values are plotted logarithmically, the line of best fit will be of exponential form and will therefore appear linear on semi-logarithmic paper, as shown above in Figure 1. The absolute value of the reciprocal of the slope of this line will be the Z-value.įigure 1, D-values at 121, 124, and 129C plotted against Temperature The Z-value can be found by plotting D-values against temperatures on a semilogarithmic scale and adding a line that best fits the data. For example, if the Z-value of a population is 10 degrees, then increasing the sterilization temperature 10 degrees will result in a log reduction of the D-value. In the practical sense, it is a measure of how susceptible a spore population is to changes in temperature. A Z-value is defined as the number of degrees (Celsius or Fahrenheit) required to change a D-value by one factor of ten.
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