University of California

Ask the Produce Docs (General)

Could onions grow black mold from being stored at too cold of temperatures for several 6 hr. periods while in transit?

Category
  • Transportation
Question

I am wondering if someone from your group of specialists could give an opinion as to whether subjecting dry onions to two 6 hour periods of 36 degree temperatures on day one and day two of a 5-day trip (by motor carriage) would cause onions, which were stored at the instructed 60 degree temperature for the remainder of the trip, to show 24% black mold (17% serious) and 11% decay, for a checksum of 35%, including 28% serious. (D.N.)

Answer

Five days would not seem adequate to explain the extent of Black Mold development and advanced decay of dry onions even after allowing for the introduction of fluctuating cool and warm conditioned air without predisposing conditions prior to loading. Even under high humidity conditions at temperatures above 70F or following wounding and exposure to temperatures above 50F, it typically takes Aspergillus niger (Black Mold) a few days to develop significant superficial growth or decay.  If the trailer “box temperature” was recorded as 36F on consecutive days with warmer temperatures between this cycle one may consider the potential for localized freezing to occur if supply air stream is below 32F and rapid soft rot to develop in a few days on warming.
                                                                                                                –Trevor Suslow

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