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Food Focus August 2008

Turkey goes belly up

Improper cooling is one of the leading contributors of foodborne illness in retail food establishments. Some bacteria produce spores that are very resilient and proper processes must be followed in the kitchen if diners are not to fall ill

A good example of what can happen if safe food practices aren’t followed occurred in a case that went before the court recently.

In 2006 a restaurant provided a Christmas Day luncheon for about 110 diners, serving a buffet with a selection of ham, beef and turkey. The next day the restaurant owner received telephone calls from diners who complained of illness after the luncheon. In all, around half the diners (57) had varying degrees of stomach pain, abdominal cramps and diarrhoea.

A Health Protection Officer (HPO), called by both the restaurant and diners, determined that the symptoms of illness described by the complainant diners were consistent with food poisoning. Indeed, the symptoms were clearly consistent with those caused by Clostridium perfringens.

Determining the type of bacteria involved can help investigators verify the cause of the outbreak and they can then put in place steps to prevent it happening again. The HPO therefore took samples from the food remaining from the Christmas Day luncheon and subsequent analysis found C. perfringens in the turkey. The level was such that it was highly likely that eating the food would result in foodborne illness.

Symptoms of C. perfringens food poisoning include diarrhoea and severe abdominal pain, only rarely is there vomiting and nausea. (For more about C. perfringens see the article ‘Bulk cooked food can breed bulk bacteria’.) Faecal samples were obtained from two of the ill diners and C. perfringens enterotoxin was found in both. While C. perfringens can be found in the stools of normal people, the enterotoxin is only found in people with C. perfringens food poisoning.

Dr Roger Cook, NZFSA Assistant Director (Science) and Principal Adviser (Microbiology), giving evidence at the trial agreed that the primary symptoms of stomach cramps and diarrhoea, experienced within 18 hours and lasting for less than 24 hours, were all consistent with clostridial toxicity.

Food safety message: C. perfringens spores are very resilient and can survive cooking temperatures – some spores can even survive boiling for an hour. They only need seven minutes to double in numbers under optimum conditions, such as holding food to between 30°C and 50°C rather than quickly cooling the food to 5–12°C. In New Zealand nearly all outbreaks of C. perfringens foodborne illness have been caused by inadequate cooling followed by inadequate reheating.

With C. perfringens identified as the culprit, the next step was to find out how it was allowed to grow.

The investigator asked about the cooking processes for the luncheon and found that three turkeys had been adequately thawed in the fridge for three or four days prior. The turkeys were then stuffed and cooked at 160–170°C for about 1 hour 30 minutes.

Food safety message: Cooking guidelines for frozen turkeys give a minimum cooking time of 2 hours 40 minutes (and for the size of bird used in this case 3 hours). The bird is cooked when a skewer is inserted and the juices run clear. Better still, use a food thermometer, the temperature should be at 82°C or above. (Recommended cooking times are increased for stuffed birds by 5 min/kg.)

The turkeys were removed from the oven and left on a high shelf in the kitchen, supposedly to cool, for about 8 hours. (Bacterial growth models suggest that this actually encouraged the bacteria to grow to unacceptable numbers over that period.) The turkeys were then reheated on Christmas Day for about 30–45 minutes at 160–180°C.

Dr Cook stated at the trial that the “preparation, cooking, cooling and holding procedures described were consistent with conditions likely to result in bacterial foodborne illness; indeed toxicosis”.

The first turkey served to diners was still “a bit pink” inside so the other two turkeys were put back into the oven for a further 20–30 minutes before also being served at the buffet. Unfortunately this was still insufficient to kill off bacteria in the centre of the turkey and stuffing.

Food safety message: Hot cooked foods will always be in the temperature danger zone (4–60°C) during cooling – there is no way of avoiding this. Therefore, foods need to be cooled as quickly as possible to escape this zone. Bacteria only need about 4 hours to grow to high enough numbers to cause illness.

Not all the diners who fell ill ate the turkey, and not all who ate the turkey fell ill. But a number of those who did eat the turkey said it appeared uncooked or pink. Those who didn’t fall ill may have eaten the outside well-cooked part of the turkey. Diners also said the person serving the meats at the buffet used the same knife to carve all the meat, including the ham and beef; potentially cross-contaminating them from the contaminated turkey.

Food safety message: To prevent cross-contamination different utensils should be used with different foods. If bacteria have grown on one food they can be transferred to other foods via utensils and equipment, increasing the risk to diners of being exposed to a foodborne disease. It is particularly important to contain any meat juices, for instance, and not spread them. Knives for slicing meat and tongs for serving should only be used on the same food and not shared.

This luncheon had all the hallmarks of an outbreak in waiting.

The timing of this luncheon may have been an added factor in this case. Christmas is a busy and stressful time in the hospitality industry when staff and kitchen space are both stretched. It is at times like these when good procedures need to be in place and staff adequately trained to follow them.

The lessons to be learned from this case are that food needs to be cooked properly and that hot cooked foods need to be cooled as quickly as possible to prevent bacteria growing. Careful monitoring of both time and temperature will help control the growth of illness-inducing organisms.

Note: There was sufficient evidence to bring a case to court and the restaurant owner was charged with selling contaminated food under the Food Act 1981, Sections 9(4)(a) & 9(5)(a). He was subsequently convicted.

Cooling down hot food and reheating

International best practice for hot foods not used for immediate service is to make sure food is cooled from 60°C to 21°C within 2 hours and from 21°C to 4°C within 4 hours.

If hot prepared food has not been cooled within these times it should be thrown away.

Methods for reducing cooling times include:

• blast chillers

• walk-in coolers

• using containers that transfer heat, eg stainless steel

• putting food in shallow pans to spread it out

• transferring food into smaller containers

• placing the hot food container in an ice bath

• stirring while cooling.

Food must pass through the temperature danger zone as quickly as possible.

When reheating cooled food it must be reheated quickly or maintained at 60°C or hotter.

Use a thermometer to make sure food has reached the correct temperature. Reheated poultry must reach an internal temperature of 82°C or above.