Pasteurize temps too high?

[Cbee]

I’m pasteurizing DIY after canning. Basic water submersion. I do a semi sweet cider and obviously do not want re-fermentation obviously. Is 145* for 10 min enough to kill that yeast? Any suggestions would be appreciated. Love to do lower temps if it would get that yeast!

[dick murton]

Effective pasteurisation is not that simple. For a start, the amount of heat you require at pasteurisation temperature (time & temperature) is dependent on the number of microorganisms, in this case, predominantly, but not limited to yeast. Like it or not, there will also be bacteria in there. The more organisms present, the greater the amount of heat treatment required - a near logarithmic factor. Then what kills one organism, say a culture yeast cell, may not kill some wild yeasts or bacteria reliably. Fortunately in brewing, most organisms viable in fermenting wort / beer require virtually the same number of Pasteurisation Units (PUs) to kill an individual cell. 1 PU = 1 minute at 60 deg C. Most brewing yeasts will be killed by application of 1 PU. Because of the numbers game, the big brewers beers will be near sterile before being pasteurised so are only treated with around 15 PUs.

Now the next problem. In bottle or can, pasteurisation is only effective when all the beer in the package receives the minimum specified number of PUs, but with the rest of the beer receiving virtually no more than this value to prevent pasteurisation induced flavour changes - particularly related to Total Package Oxygen (TPO). Typically the coldest spot is about half an inch above the base of the bottle or can in a drench shower style pasteuriser, probably somewhere more like the middle of teh bottle / can if fully submersed. So it takes a while to progressively heat up the entire contents evenly, perhaps 15 to 20 minutes, hold at the required temperature for a specified time to give the required heat treatment (number of PUs) and then cool progressively but more rapidly rapidly to minimise over-pasteurisation and flavour changes. Just putting the bottles / cans in hot water for 10 minutes will barely start to warm the beer, let alone pasteurise it. Tunnel pasteurisation typically takes about 45 minutes in total, including 15 to 20 minutes at circa 62 to 67 deg C for the pasteurisation zone (according to the number of PUs required) though may be longer depending on the efficiency of design of the system

[ASC]

Thank you for that information. I thought PU had to be higher. 25-50 so good info for me


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[dick murton]

Have a look at this to give an idea of how to estimate the number of PUs required, from which you use a temperature / time / PU chart to give you a starting figure. By monitoring flavour, non biological haze etc. and the biological quality, all during the desired shelf life of the beer, you can jusde if you need to improve the quality of pre-pasteurisation treatment or perhaps increase the number of PUs.

The PU specification is set to deal with the worst case found.
In the following example, lactic acid bacteria, with a D₆₀ value of 4 minutes, are occasionally found at levels of up to 100 cells /100 ml. A target reduction in micro-organisms to less than 1 cell / 50 litres is required. The PU calculation is as follows:
initial loading (lactic acid bacteria) = 100 cells /100 ml = 50,000 cells / 50 litres

if 4 PUs reduces the population by 90 % (decimal reduction, where D60 = 4), then 5 x 4 PUs are required to reduce the population to 0.5 cells / 50 litre. Therefore the target PU level required, in this example = 20.

If however, the organism had a D₆₀ value of 2, then only 2 PUs would be required to cause a decimal reduction, and 5 x 2, or 10 PUs would be enough to reduce the above population to 0.5 cells / 50 litre. Therefore the minimum PU level required, in this example = 10