Salty shrimp and food safety.

From J., 6 August 2011, dried shrimp – will they kill our guests?

Q: Having a dinner party and serving Thai food. I’m making green papaya salad and bought a little bag of dried shrimp, as the recipe requires. The packet says to “always cook or fry” before serving.

The recipe calls for the dried shrimp to be pounded and combined with the other ingredients, without cooking. Am I going to poison our guests?

A: Hi and thanks for your question. Dried shrimp are one of those ingredients, common to several Asian and African cuisines, that doesn’t get a lot of play elsewhere (although you will see it in some Louisiana recipes, possibly as a reflection of African influence). Dried shrimp should not be confused with the brine shrimp found in the refrigerator section of Korean groceries, used to jump start the kimchi fermentation process (as well as adding savor).

Anyway, to your question. Dried shrimp are like any other dried product – lacking water, they are not hospitable to pathogens. The amount of water that must be present in a substance to support microbial growth varies by microbe, and usually is expressed in terms of the substance’s “water activity” (aw). Water activity does not correlate perfectly with moisture content. Bacteria and molds can grow in substances with aw of .8 or higher. At an aw of .5 or lower, most microbes cannot proliferate.

So, on to the dried shrimp. I don’t know the aw of dried shrimp, but dried fruit and other dried foods generally have aw around .5 to .6. Honey, by comparison, has aw of about .6, and salt-saturated water an aw of .75, demonstrating that moisture levels do not correlate perfectly with water activity. In any case, you can feel quite sure that your dried shrimp is not going to make anyone sick, as long as you don’t expose it to any new pathogens, such as through using a dirty cutting board or touching with unwashed hands (cross-contamination).