FOOD SAFETY IN CHILLERS…..

There is a widespread (but misplaced) belief in the food manufacturing, retail and hospitality sectors that walk-in cold rooms are the definitive panacea for storing all kinds of perishable foodstuffs. Much like salt (which was used to preserve meat on long sea voyages but had limitations), all types of refrigerated goods suffer a similar fate. Why?

Refrigeration science has not advanced to the point where desirable humidity levels can be stabilised and maintained 24/7 and where airborne bacteria, food spoilage acid and gas can be removed (the presence of the latter gives rise to the typical odours/smells that are present in cold rooms despite the most stringent cleaning regimes).

Fruit, vegetables, berries, cakes, pastry, fish, chicken, dairy products and prepared food stored at an ambient temperature range of 2°C to 5°C (with a core temperature variance of 2°C) and 78% to 88% relative humidity maintains maximum quality. Hanging meat requires 2°C and 80–85% relative humidity to maintain maximum weight and quality. Under these conditions ageing slows down and bacteria growth is greatly reduced.

Whilst modern walk-in cold room technology has advanced to the point where ideal temperature and humidity levels can be preset, these cannot be maintained 24/7 due to frequent door opening (even those left open for extended periods during peak production); ageing and overworked refrigeration plants; irregular or non-existent plant maintenance and constant, high traffic volumes in and out of the cold room.

As a result, moisture builds up during busy work shifts developing pockets of latent heat (“hot” spots ), which result in ambient temperatures exceeding 5°C (and 2°C).

Hot air rises but, in a cold room, the warm air entering the area (even where drop temperatures are utilised in production areas, air will be warmer than that of a cold room), remains nearer the floor, bouncing off the prevailing stream of cold air blowing off the evaporator or chiller fans. The warm air eventually moves around the cold air stream and that is when condensation (which is not always visible) settles on the walls and ceiling, dripping onto the floor and onto all exposed foodstuffs, which becomes the ideal breeding ground for bacteria and mould formation.

This is exacerbated in chillers when surplus condensation spews off sizzling, moisture-laden ingredients during the rapid cooling down process.

Conversely, when cold room doors remain closed for hours on end the evaporator fans dry out the inner air and, when conditions become too dry, all exposed perishables give up moisture – that is why baby marrows become limp and lettuce and spinach shrivel while hanging meat shrinks, dries out, discolours, drips blood and loses weight.

So, during the “day” the air in the cold room is usually too moist and at “night” (after hours) the air is usually too dry. Relative humidity levels vacillate in tandem alongside equally fluctuating vapour pressure levels which creates a “push” effect when conditions become too moist and, conversely, when conditions become too dry a “pull” effect. This eventuates in blood purge in  vacuum/Cryovacpackaged meat and natural juice purge in vegetable pillows.

Vegetables, fruit, herbs, berries and flowers produce ethylene gas that acts as an ageing hormone, fostering growth. Each plant species has differing production rates and varying absorption capabilities. Post-harvest edible plants continue producing ethylene gas as a ripening agent. Excessive production levels of ethylene gas has the destructive capability of shortening the shelf-life of most plant species stored in cold rooms, leading to food spoilage and loss of revenue.

Suppliers also unintentionally introduce spores, moulds and yeasts into cold rooms via cartons, crates, pallets and packaging material. Airborne bacteria rapidly disperse in a cold room by attaching themselves to the water molecules in the air – this gives rise to cross contamination, cold room odours and (in the case of Staphylococcus aureus) food poisoning.

Hanging meat has a high incidence of bacteria on the surface, which (in the presence of moisture) causes sliminess on exposed lamb and pork and ultimately carcass spoilage. Fluctuating moisture levels are the direct cause of meat shrinkage, discolouration, dripping blood and weight loss.

Fresh fish has loads of natural bacteria present on its surface and, in the presence of excess moisture and unstable ambient temperatures, these rapidly multiply and lead to texture spoilage.

These examples apply to all types of refrigeration, whether brand new or old, and that is why, in particular, walk-in cold rooms are both perfect and imperfect facilities for food storage. Cold rooms can keep fresh and prepared food relatively cold but cannot prevent cross contamination and food spoilage from taking place.

References

Sylvia Blankenship. Ethylene–the ripening hormone. Paper presented at the 16th Annual Postharvest Conference 2000, Yakima, WA (http://postharvest.tfrec.wsu.edu/pages/PC2000F)

Meat Inspectors Manual: Red Meat, Directorate: Veterinary Services, Veterinary Public Health, National Department of Agriculture, Republic of South Africa, January 2007, Temperature control and storage of meat, p. 137.

USA Food and Drug Administration: Programme Information Manual Retail Food Protection: Recommendations for the temperature control of cut leafy greens during storage and display in retail food establishments, July 7, 2010, pp. 1–3.