Immersion in water that is less than 10 degrees warmer than the tomato will allow an osmosis effect to allow water to enter the tomato thru the stem. If there were biological hazards on the outside of the tomatoes being washed there is a chance of that hazard being carried into the tomato itself. Note that this is for immersion (submersion) into water, a spray rinse is not considered immersion and does not have this requirement. If you are a farm or packing from the farm you pretty much need a flume to get the produce clean as spraying is not anywhere near effective enough to treat and clean. Hence the temperature and sanitizer hourly monitoring. In a repacking facility, product is typically spray rinsed again with a sanitizer that must be monitored due to customer requirements and best practices.
Tomato Metrics: http://www.fda.gov/d...n/UCM171708.pdf Section 7 Packinghouse, Item 7 Postharvest Washing of Fresh Tomatoes, C, iii:
c. Temperature and Disinfection of Water Supplies Used in Postharvest Applications. Internalization of bacteria into the stem scar has been demonstrated with tomatoes submerged in water that is cooler in temperature than the pulp of the tomato. When the tomato cools, a vacuum is created causing water, and potentially pathogens, to be drawn into pores on the tomatoes. Therefore, water temperature relative to pulp temperature, and water quality, are critical considerations for maintaining the safety of the product.
i. The water used for washing tomatoes "SHALL" be of microbial quality equivalent to potable water and have sufficient sanitizer to prevent cross contamination. The water antimicrobial "SHALL" be monitored at a frequency sufficient to maintain sanitary conditions.
ii. Cold water immersion as a cooling technique "SHALL" not be done.
iii. Water temperature "SHALL" be maintained at least 10ºF warmer than the pulp temperature of the tomato. Water temperature "SHALL" be monitored at least hourly.
From the Packinghouse Procedure:
7.10 REQUIREMENT In systems where tomatoes are submerged or dwell in water, water temperature is monitored and controlled. Water temperature should be at least 10ºF above highest measured pulp temperature of tomatoes when entering the water. If operation can demonstrate retention times are never more than two minutes and water submersion does not exceed 1 ft, water temperature "SHALL" be controlled to be not less than highest measured pulp temperature.
PROCEDURE Operation shall have methods for determining pulp temperature, a procedure for control of water temperature, shall monitor temperature at a prescribed frequency sufficient to assure continuous compliance and shall maintain records of water temperature. If water is maintained at less than 10ºF above pulp temperatures, the operation "SHALL" maintain records substantiating that dwell time and depth standards have been met, and tomatoes have not been washed in water at temperatures less than the highest measured pulp temperature. Operation "SHALL" have a procedure as to what corrective actions are taken if criteria are not met. Water spray or shower systems,
wherein tomatoes are not submerged or dwell do not require temperature control.
VERIFICATION Auditor shall review the procedure and shall review records of temperature monitoring. Auditor observes process including the operation’s sampling of pulp
and water temperatures. Auditor reviews records for deviations and their disposition.
CORRECTIVE ACTION/DISPOSITION Procedure is developed or revised. Retraining is performed. Tomatoes washed in water at temperatures less than the highest measured pulp temperature "SHALL" be discarded back to the last evidence of compliance.
I see the word "should" in the previous posts concerning water temperature for tomato immersion. A good HACCP or HARPC plan must identify this hazard and take steps to control it with the word "shall"