cooling curve
Pete Snyder
Mike, Barbara, John, and foodsafe
The cooling curve for food is actually not linear; it is log-linear. The mathematics are explained by Pflug and Blaisdell in their paper [Pflug, I.J. and Blaisdell, J.L. 1963. Methods of analysis of precooling data. ASHRAE J. 5(11):33-40, 49] and also Dickerson and Read [Dickerson, R.W. and Read, R.B. 1973. Cooling rates of foods. J. Milk Food Technol. 36(3):167-171].
When one plots 6-hour FDA Food Code cooling from 135 to 41F, it turns into a straight line on log paper, as pointed out in the Pflug and Blaisdell, and Dickerson and Read, papers.
I have incorporated a graph and table at the end of this email, showing the plotted cooling time-temperatures for 135 to 41F and also for the USDA cooling, 120 to 55F in 6 hours. You can see that cooling higher temperatures is very fast, 135 to 94 in the first hour, 6-hour cooling, vs. 120 to 101 in the first hour, 120-to-55 cooling in 6 hours, with continuation until the center temperature is 40F. This is about 14.16 hours from 120 to 55F, with continuation until 40F center temperature is reached, which USDA allows and is safe for large roasts. Note that the driving force of the cooling water or blast air stream is a critical item to include in the calculation when one considers cooling.
When you use this log cooling data for Mike Peck's Clostridium perfringens predictor program in ComBase, there is less than 1 log increase in the 120-to-55F USDA 6-hour cooling process with continued cooling to 40F. It is essentially zero increase in the 6-hour 135-to-41F cooling.
Note that in the cooling curves, I have assumed a driving force of 38F, because this is the average temperature for walk-in and reach-in refrigerators. The compressor turns on at 40F and off at 36F, with an average temperature of 38F. If one is using an ice bath, the driving force temperature is 32F. The data plot even nicer in and ice bath with a steady 32F.
Pete
COOLING TIMES AND TEMPERATURES
|
FDA
6-Hour Cooling
57.2 to 5.0 °C (135 to 41ºF) [3.3°C (38ºF) Environment] |
USDA
Cooling
48.9 to 12.8°C (120 to 55ºF) in 6 hours, followed by cooling to 4.4°C (40ºF) [3.3°C (38ºF) Environment] |
||
| Hr. | °C (°F) | Hr. | °C (°F) |
| 0 | 57.2 (135) | 0 | 48.9 (120) |
| 1 | 34.4 (94) | 1 | 38.3 (101) |
| 2 | 21.1 (70) | 2 | 30.0 (86) |
| 3 | 13.2 (55.8) | 3 | 23.9 (75) |
| 4 | 48.9 (8.0) | 4 | 18.9 (66) |
| 5 | 6.39 (43.5) | 5 | 15.6 (60) |
| 6 | 5.0 (41) | 6 | 12.8 (55) |
| 7 | 10.6 (51) | ||
| 8 | 8.9 (48) | ||
| 9 | 7.5 (45.5) | ||
| 10 | 6.61 (43.9) | ||
| 11 | 5.83 (42.5) | ||
| 12.6 | 5.0 (41) | ||
| 14.16 | 4.4 (40) | ||
[Foodsafe] Foodsafe- cooling meatloaf.eml
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Subject: [Foodsafe] Foodsafe- cooling meatloaf |
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From: "barbara lund (IFR)" <barbar...@ifr.ac.uk> |
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Date: Thu, 5 Apr 2012 09:03:34 +0000 |
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To: "Foodsa...@googlegroups.com" <Foodsa...@googlegroups.com> |
Foodsafe group.
The concern about this process is that spores of Clostridium perfringens will survive the cooking process and can germinate and give growth of vegetative bacteria during a slow cooling process.
Work by Professor Mike Peck’s group at the Institute of Food Research UK has provided a model that enables the effect of any cooling process on the increase in numbers of C.perfringens to be calculated.
Below is information from Mike Peck on this.
“Please see Perfringens Predictor at www.combase.cc. This can be access freely. This programme has been specifically developed to predict the growth of C.perfringens during the cooling of bulked meats. This model has been peer reviewed and published in the scientific literature.
If one inputs a linear drop from 80°C to 60°C in 2 hours into Perfringens Predictor, followed by a linear drop to 5°C in 7 further hours. Then there is a 2-3 log increase in counts of C.perfringens. Based on risk assessments carried out internationally, the maximum increase that is acceptable is one log, so this would not comply with generally accepted safe practice. However, this prediction is based on a linear drop in temperature and pH6.5 and 1% NaCl. A more reliable prediction must be obtained by inputting your actual temperature cooling curve, and preferably also the pH and NaCl concentration. A lower pH and/or high salt concentration may result in less growth. If a lower pH and/or high salt concentration are used as CCPs, they will need to be monitored.
If instead one inputs a linear drop from 80°C to 60°C in 2 hours, followed by a linear drop to 5°C in 4 further hours. Then there is a 0.8 log increase in counts of C.perfringens. If one inputs a linear drop from 80°C to 60°C in 2 hours, followed by a linear drop to 5°C in 2 further hours. Then there is <0.1 log increase in counts of C.perfringens. Both of these comply with what is generally accepted as safe practice (and are based on a linear drop in temperature and pH6.5 and 1% NaCl).”
Best wishes
Mike
-----------------------------------
Professor Mike Peck
Deputy Leader, Gut Health & Food Safety
Institute of Food Research
Norwich Research Park
Colney
Norwich, NR4 7UA
United Kingdom
tel: 44-(0)-1603-255251
fax: 44-(0)-1603-255288
email: Mike...@ifr.ac.uk
Our website is: www.ifr.ac.uk
e-disclaimer at http://www.ifr.ac.uk/edisclaimer/
Microbes Norwich www.micron.ac.uk
FHN Network www.foodandhealthnetwork.com
Dr Barbara M. Lund,
Visiting Scientist,
Institute of Food Research,
Norwich Research Park,
Colney,
Norwich NR4 7UA.
e-mail: barbar...@ifr.ac.uk
-- O. Peter Snyder, Jr., Ph.D. Hospitality Institute of Technology and Management 670 Transfer Road, Suite 21A; St Paul, Minnesota 55114; USA http://www.hi-tm.com Tel 651-646-7077 FAX 651-646-5984 One worldwide uniform set of retail food safety guidelines
Carl Custer
For the sociologists and cowboys out their, as the temperature drops
the delta T becomes smaller thus the heat transfer rat becomes
smaller. Think Zeno's paradox.
Once upon a time before Vijay & Pete's program, I cobbled "Cool Calc"
using Lotus 123 for evaluating cooling deviations.
Known temperatures were put in one column, the next column calculated
the Log values, the third column filled in between the log values. and
the fourth column calculated the incremental Cl. perf increase, using
a column of Busta's data, and summed the increments. Kinda crude, we
called it "Cowboy calculus" but it was what we had.
Pete Snyder
the cooling curve. But when you plot the log curve it should come out
nice and straight in a log plot, and if it doesn't you know the
experiment was not done correctly or won't match actual operating data.
Pete Snyder
----------------------------
mike peck (IFR) wrote:.
> Thanks everyone. Sorry for any confusion. Colleagues are, of course, correct to point out that cooling is not linear. However I was reluctant to provide more detailed advice without details of the actual cooling curve. I did (and still) suggest that the actual cooling curve is input to Perfringens Predictor.
>
> Thanks Mike
> ________________________________________
> From: Carl Custer [carl....@gmail.com]
> Sent: 05 April 2012 19:40
> To: Pete Snyder
> Cc: foodsafe; barbara lund (IFR); mike peck (IFR); John Merritt; Harris, Craig
> Subject: Re: [Foodsafe] cooling curve
>
> Thanks Pete,
> For the sociologists and cowboys out their, as the temperature drops
> the delta T becomes smaller thus the heat transfer rat becomes
> smaller. Think Zeno's paradox.
>
> Once upon a time before Vijay& Pete's program, I cobbled "Cool Calc"
> using Lotus 123 for evaluating cooling deviations.
> Known temperatures were put in one column, the next column calculated
> the Log values, the third column filled in between the log values. and
> the fourth column calculated the incremental Cl. perf increase, using
> a column of Busta's data, and summed the increments. Kinda crude, we
> called it "Cowboy calculus" but it was what we had.
>
>
> On Thu, Apr 5, 2012 at 2:15 PM, Pete Snyder<osn...@hi-tm.com> wrote:
>> Mike, Barbara, John, and foodsafe
>>
>> The cooling curve for food is actually not linear; it is log-linear. The
>> mathematics are explained by Pflug and Blaisdell in their paper [Pflug, I.J.
>> and Blaisdell, J.L. 1963. Methods of analysis of precooling data. ASHRAE
>> J. 5(11):33-40, 49] and also Dickerson and Read [Dickerson, R.W. and Read,
>> R.B. 1973. Cooling rates of foods. J. Milk Food Technol. 36(3):167-171].
>
--
O Peter Snyder, PhD
Hospitality Institute of Technology and Management
670 Transfer Rd, St Paul Mn 55114
Tel 651-646-7077
email: osn...@hi-tm.com
Carl Custer
temperatures fell along a log straight line. A few times they didn't
(Cthulhu only knows how the cowboys stuck the temperature probes in
:^)
Ahmad Tahajod
Dear Food Safe,
Just as reminder USDA preferred recommended guideline for cooling of meat and poultry ( FSIS Directive Appendix B) is 130F to 80F in 1 ½ hour and 80 to 40 F is 5 hours, therefore total time is 6.5 hours for cooling from 130 F to 40 F.
Ahmad Tahajod, Ph.D
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Peter Snyder
It is true that the the USDA says that their recommended cooling is 130F to 80F in 1.5 hours and 80 to 40F in 5 more hours because it is safer. But the facts are that when you want to cool bigger diameter meats, you can't do it using the 6.5 hours. When you evaluate the ComBase predictor (Mike Peck) for predicting safety the 120F to 55 in 6 hours is less than one log increase of perfringens and is safe.
Pete Snyder
-- O. Peter Snyder, Ph.D. email: osn...@hi-tm.com Hospitality Institute of Technology and Management URL: http://www.hi-tm.com 670 Transfer Rd, St Paul MN, 55114 Tel: 651-646-7077 FAX: 651-646-5984 One worldwide set of validated food safety procedures