A quick change in temperature

I have always assumed that every part of a grocery store, including the store room in the back, was climate controlled with regular air conditioning.  Granted I know that some smaller businesses may have their own protocols that may differ in this regard, but at least with large chain grocery stores, I just always assumed that air conditioning in store rooms was a standard.  I found out otherwise last month when I brought home a few boxes of cereal that smelled a little “off” right when I opened the tops up one by one consecutively after noticing it on the first. I knew I could recognize it, the blend of that with the smell of the cereal was throwing me off.  Then I remembered what it was: mildew. I looked closer inside the boxes and could see white and green mold spots on various parts of the insides of the boxes. I was absolutely shocked at what I found and Immediately took it back to the store. They were apologetic but something seemed strange about the employee’s reaction to the boxes of cereal, as if this wasn’t the first time he had seen this sort of thing.  I probed him a little bit and asked how it can happened in a dry and cool store room with no sources of moisture inside the boxes besides ambient air. It turns out that their store room is not dry and cool and instead is the opposite, hot and muggy. Apparently they had a recent leak from their overhead HVAC system and some products were affected, they were just still trying to determine what got shelved before the problem was detected.  They gave me my refund and apologized but it left me with more questions, in particular–how common is this? Is it safe to leave dry food and groceries stored in 80% humidity like that?

HVAC maintenance