Question
We are in the process of setting up a food coop and have been gathering information about produce handling procedures. It seems to be common practice among a couple coops we have visited to immerse newly delivered leafy greens in lukewarm water. This is done, I presume, to firm up the texture of potentially wilted produce and to lengthen shelf life. I have a couple questions about this:
1) If the product is going straight to the display cooler and not into a walk-in cooler, is this still advisable, given that the immersion warms up the product?
2) Is immersion still a good idea if the product has been kept well chilled and shows no wilting? Mostly my concern here is about the potential risk of contamination from additional handling.
Any advice you could give me would be greatly appreciated. Your website has been immensely useful over the last year, but I could not find information on this specific question. (M.D.)
Answer
Probably there is no single answer, since there are always details in a particular handling system that could make a difference. It is true that leafy products absorb warm water more rapidly than cold water, but the difference due to temperature is not large. Most leafy products will absorb cold water easily and therein lies the concern with hydrocooling and sanitation. I would harvest and handle the product so that the water immersion step is not needed. Pay attention to protecting it from water loss in the field (where water loss rate is high). Harvest in the morning when cooler and protect product from direct sun and air movement. Use a paper or plastic cover to the crate or carton or use a thin plastic liner in the carton box. Also reduce the time from harvest to moving to product into a cold room—reduce all delays to cool.
With those general comments, here are my answers to your questions:
1) If the product is going straight to the display cooler and not into a walk-in cooler, is this still advisable, given that the immersion warms up the product?
I am assuming the lettuce is displayed as single heads and that its temperature is 50-70F (10-68C) range after water immersion (I would use cold rather than warm water). Then it likely will cool to the temperature of the display cooler fairly quickly; the cooler should be managed so there is rapid turnover and in your case I would guess you do not need long shelf-life. So even if the lettuce did not cool down to ideal temperature (below 41F), shelf-life and quality would still be adequate.
2) Is immersion still a good idea if the product has been kept well chilled and shows no wilting? Mostly my concern here is about the potential risk of contamination from additional handling.
In this case there is no need or advantage to freshen the product with a water immersion and I agree about increasing the contamination risk. We manage using the principle of “cold and dry” to minimize bacterial growth on leafy greens and others.
Frankly many consumers do not like water on their leafy greens although misting systems are used in some supermarkets. The water often leads to more rapid browning and decay (depend on temperature and lettuce quality).
In summary I would suggest focusing on minimizing water loss during postharvest handling and not immersing the heads. If you find that is not possible without significant quality loss and dehydration, then yes pay attention to the water sanitation. Frequent changes of water will help but if doing a batch system you would want to include a disinfectant.
Check out some of the sanitation related publications by Trevor Suslow at http://ucfoodsafety.ucdavis.edu/.
-Marita Cantwell