![]() In the above case the Z-value appears to be approximately 8☌. 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. The number of PU's required for a particular beverage depends on several factors. It was defined in 1951 by Del Vecchio et al,1 and is employed in rating the effectiveness of pasteurization processes for beer and other products. In reality however, D-values will not decrease perfectly due to natural variations and experimental error. One pasteurization unit (PU) is the microorganism death that occurs in a product held at 60C (140F) for 1 minute. 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 reference temperature, Z-Value and the process duration parameters (if one wants to use the PU. (At 121.11☌), and 20 pasteurisation units are equivalent to exposing the product for 20 minutes at the reference temperature (normally 60☌). Software programs that automatically analyse. 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. First, we need to understand what a PU is and have a system for measuring them. the calculation of equivalent thermal processes. ![]() 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. No information on contributors is available for this page.A Z-value is defined as the number of degrees (Celsius or Fahrenheit) required to change a D-value by one factor of ten. The object of this work was to elucidate whether the biological impact of different flash pasteurization procedures can be compared by PU calculations over the temperature interval from 50 to 90☌.” “It is now clear that the pasteurization unit is certainly not a good descriptor of product damage by thermal stress. Journal of the Institute of Brewing, vol. The biological impact of flash pasteurization over a wide temperature interval. Method 13.37, Measurement of Pasteurization Units (PU's). Piggott, editors.įermented Beverage Production. k) Compute the holding time for milk from the following formula. Proceedings of the American Society of Brewing Chemists, 1951, page 45.Ģ. unit pasteurizes two or more dairy products requiring different pasteurization temperatures. Thermal death time studies on beer spoilage organisms. In reality, of course, the beverage does not instantaneously go to the desired temperature, nor does it cool down instantaneously.ġ. T is the time in minutes at which the beer is held at that temperature. Where T is the temperature in degrees Celsius, and The total number of PU's for a particular pasteurization processs for beer can be estimated from²: In Section 4, two worked examples are presented on how to use an F value when calculating the actual sterilization time Pt: - C.R. Unfortunately, higher temperatures tend to affect the taste of the beverage. Calculate heat required to elevate temperature from. It is a tradeoff: high temperatures for short times or lower temperatures for longer times. The example is based on 1 ton of sludge cake at 18 percent dry solids. The success of pasteurization (that is, what percentage of the microrganisms are killed) is affected by both temperature and by the length of time for which the product is held at that temperature. A survey of large American breweries in 1955 found their processes averaged 14.8 PU's, wih a range of 2.4 to 45.6 PU's. “Wild” yeasts, for example, such as occur in some types of Belgian ales, are more resistant to heat than domestic yeasts. Holding cell (heat retention unit) calculation 4. ![]() The number of PU's required for a particular beverage depends on several factors, such as the microrganisms it contains and even on the type of packaging. Calculation of equilibrium pressure (dissolving power) of CO2 in water. It was defined in 1951 by Del Vecchio et al,¹ and is employed in rating the effectiveness of pasteurization processes for beer and other products. One pasteurization unit is the microorganism death that occurs in a product held at 60☌ for 1 minute. ☙ Share this page on Facebook pasteurization unit ![]()
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |