Hi,
PU unit is defined as one-minute exposure to temperature of 60°C. The formula is 1,3932(T-60), , where T is pasteurising temperure. There is approximately ten-fold increase in sterilising effect for every 7°C increase in temperture.
Different products are pasteurised at different temperature, lager beer is normally pasteurized at 60-62°C, but with low-alcohol beers and malt beverages higher tempertures are used.Typically 64-70°C
Minimum PU to achive microbiologically stable beer has been determined to be around 5-6 PU but typically brewers aim for 15-20 PU, with 10 as the minimum.
Care must be taken to measure the temperature in the "cold spot" of the container which is normally situated about 2 cm above the bottom. (see pic)
The product affects the required PU. pH, CO2 and alc. level all affect the lethal rate of micro-organism. High sugar containing products also need higher PU.
Some brewers only calculate the PU for 60°C and above but I think more commonly above 50°C is used.
Its not possible to give a figure for when beer is scalded. Pasteurization flavor has been described as oxidised, bread crust like, cardboard/papery or cooked. But the level of these flavors is highly depended on the oxygen content of the beer. In extreme cases prolonged pasteurising in the presense of oxygen can lead to darkening of beer color. The exit temperture of the containers has also been shown to be very inportant for quality of the product, if it is too high the flavor can be effected. Common specification is to aim for <30°C in the package at exit.
Beer can be tested for if it is pasteurised, see enclosed method but the method does not tell us by how much.
Hope this helps,
regards, Baldur
http://www.redpostlt...ort/science#TDU
The following is a description and procedure for thedetermination of whether beer is pasteurized. Taken from the A.S.B.C. Proc.(1960) page 63.
PRINCIPLE: Beer, which has not been pasteurized, will containactive invertase. When sucrose is added to a beer containing invertase, thesucrose will be hydrolyzed to fructose and glucose. The presence of glucose canbe detected using glucose oxidase sensitized paper strips. The presence ofglucose in beer after sucrose addition indicates the beer has not beensufficiently pasteurized.
REAGENTS: A; Test tape for glucose - Eli Lilly & Co. B;Powdered sucrose.
PROCEDURE: A; Add 1g. Of powdered sucrose to 5ml. of beerand allow to stand for 30 minutes at room temperature. B; partially immerse ashort strip of the test tape into the beer, withdraw from the beer and observethe color after 2 minutes. C; If the test tape turns green, the beer has notbeen sufficiently pasteurized. D; For color comparison, the test should be runsimultaneously on an un-pasteurized beer sample.
