20240724-FactSheetCoolingTCSFoodCode-0733
Food Safety – Cooling Safely, A Follow-up Article
Cooling hot foods has been a major concern for food safety for decades of foodborne illness investigations. This blog has just reported a study from the Centers for Disease Control, citing a biological agent (Salmonella, E. Coli, Listeria) in 55.6% of 800 cases of foodborne illness. Of those 800 cases (2017-2019), 10.6% were related to improper cooling of hot foods. Frank Bryan found that improper cooling of food was the leading factor contributing to outbreaks, accounting for 44% of 1,918 outbreaks in the U.S. from 1961 to 1982. Data collected by the CDC between 1998 and 2008 show that improper cooling practices contributed to more than 500 foodborne illness outbreaks associated with restaurants or delis in the United States.
In sum, improper cooling is a major food safety concern. Improper cooling, cooking, holding of food and reheating all play a critical role in causing illness. The problem relates to the survival of spore-forming bacteria such as Clostridium perfringens during cooking. When food is cooked (165°F and higher), the bacteria develop a protective barrier, a spore, which can survive boiling for an hour or longer.
Spores provide C. perfringens with resistance against such common food environment stresses as low or high temperatures, osmotic pressure (dehydration processes), chemical preservatives and pH (acidic or mild environments).
While vegetative (unprotected) cells cannot survive even brief exposure to 131°F (55 °C), spores of some C. perfringens strains can survive boiling for an hour or longer. So if a food is unsafely cooled, and spores remain viable in the food, reheating the food will not make it safe to eat. In one experiment, spores were only made inactive by heating the food to 176°F for 40 minutes, a process likely to make the food inedible and a process impractical in a restaurant.
If the heated food is improperly cooled, the spores dissolve, and bacteria grow rapidly in 10-20 minutes on average in the range of 120°F. (Spores survive both refrigeration and freezing temperatures). Once the food is consumed, the bacterial cell dissolves due to the stomach’s low pH: an enterotoxin is produced, causing illness.
One study (see Olds citation) shows effective cooling procedures, using turkeys and chili. The same process was repeated three times, so there are a mean (average) and a standard deviation statistic. The author notes the qualifiers to this study. The study was conducted in a laboratory, and actual food service conditions, such as refrigerator temperature fluctuations, doors opening and closing, and cross-contamination potential, could not be considered. Also, the final cooking temperature would actually be 165°F, not 135°F.
In one study, turkey roasts were cooled using the following methods: one roast quartered, cooled in the walk-in cooler; one roast loosely wrapped, cooled in a blast chiller; one roast loosely wrapped, cooled in a walk-in cooler; and three roasts bagged, cooled in a walk-in cooler. All roasts were cooked to 57 °C (134.6°F) and cooled to 5 °C (41°F).
The mean (average) cooling times from 134.6°F to 69.8°F were as follows: 2.16, 3.06, 6.13, and 28.10 hours (less than 2 hours would be required). The mean (average) cooling times from 69.8°F to 41°F were as follows: 6.2, 9.2, 13.47, and 28.10 hours (less than 4 hours would be required). In both cases, the Food and Drug Administration cooling requirements (135°F to 70°F in 2 hours and 70°F to 41°F in 4 more hours) were not satisfied.
Microbiological analysis for Clostridium perfringens showed that the blast chiller and quartered treatments had a reduction in bacterial counts by 0.86 log to 2.7 log. The other methods showed increases. This analysis seems positive, but only for the two methods; the other treatments showed increases in bacterial growth. And, note that most wholesale and manufacturers are required to demonstrate 5 log reductions in growth.
Conclusions? The study is imperfect since it is impossible to anticipate restaurant conditions. All types of variables could affect the cooling times. The results seem to indicate, however, that safe cooling requires a combination of methods, not just reliance on refrigeration. It is not enough to put the food into refrigeration and trust the process will be safe. Two treatments might be immersing the bagged turkey into ice or further slicing up the turkey and refrigerating in a shallow pan. In all cases, managers must monitor the cooling process and make corrections, as needed, throughout. In the words of one infomercial, it is not enough to ‘set it and forget it’. That adage will not work here!
Cooling Chili:
A second study shows effective cooling procedures using chili. Chili was cooled using six treatments: (a) chili cooled in 12 x 10 x 2 ½” pan, in a walk-in refrigerator; (b) chili cooled in 12 x 10 x 4” pan, in a walk-in refrigerator; (c) chili cooled in 3 gallon stainless steel stockpot, in a walk-in refrigerator; (d) chili cooled in 12 x 10 x 2 ½” pan, in a blast chiller; (e) chili cooled in 12 x 10 x 4” pan, in a blast chiller; and (f) chili cooled in 3 gallon stainless steel stockpot, using a chill stick, in a walk-in refrigerator. Each treatment was repeated three times.
The chili was cooked to 190°F, and each treatment began immediately. The mean cooling time for each treatment (135°F to 70°F) was as follows: 2.23; 3.53; 8.00; 0.40; 1.43; and 2.10 hours.
Treatments D and E satisfied legal cooling requirements. The mean cooling time for each treatment (70°F to 41°F) was as follows: 4.57, 7.40; 16.17, 1.17; 2.30; and 4.0 hours. Treatments D and E satisfied the requirements; treatment F did not because the total cooling time was over 6 hours.
Conclusions? Again, it is impossible to replicate actual food service conditions. Placing hot food into refrigeration, even in reduced volumes, can lead to more problems: this is evident in treatments A, B and C. A blast chiller is beyond the budget of most food service operations. The study clearly shows the problems relying on refrigeration or any equipment to take the place of employee training and monitoring temperatures.
Two processes were not included in this study: using an ice water bath; and regularly stirring the foods. Stirring reduces cooling times by up to one third.
As always, I welcome your comments and questions. Please direct them to info@foodsafetymentor.com Thank you! Dave
Citations
David Olds and Jeannie Sneed ‘Cooling Rates of Chili Using Refrigerator, Blast Chiller, and Chill Stick Cooling Methods’ A paper to be submitted for publication in The Journal of Child Nutrition & Management David Olds1 and Jeannie Sneed2
‘Cooling meat products in foodservice: Time, temperature, and growth of Clostridium perfringens ATCC 10388’ by David A. Olds Master’s Thesis Iowa State University 2004
‘Quantitative Data Analysis To Determine Best Food Cooling Practices in U.S. Restaurants’ Journal of Food Protection April 2015 78(4) Donald W. Schaffner , Laura Green Brown, Danny Ripley, Dave Reimann, Nicole Koktavy, Henry Blade, and David Nicholas
FDA, Bad Bug Book, 2nd Edition. https://www.fda.gov/food/foodborne-pathogens/bad-bug-book-second-edition?trk=public_post_comment-text
Frank L. Bryan, Thomas W. McKinley ‘Prevention of Foodborne Illness by Time-Temperature Control of Thawing, Cooking, Chilling and Reheating Turkeys in School Lunch Kitchens’ Journal of Food Protection V. 37(8) August 1974