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At the grocery store here in Germany I saw that lettuce isn't refrigerated. So I brought a head home and it's been in my pantry for 3 days and it seems fine... The English speaking internet says that's not ok, I don't know what the German one says.

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In my experience, different varieties of lettuce have wildly different behaviour in this respect: Boston lettuce is quite sensitive, whereas iceberg lettuce can withstand minor thermonuclear blasts. –  Erik P. May 4 '13 at 1:24

2 Answers 2

It is all due to storage lifetime. Lettuce is particularly perishable, compared to many other vegetables.

You will get a considerably longer storage lifetime if it is refrigerated, rather than kept at room temperature.

According to the USDA:

Storage Conditions: Lettuce should be quickly cooled and maintained as close to 0 °C (32 °F) as possible with 98 to 100% RH. Head types are better adapted to prolong storage than are the other types, but none keep longer than 4 weeks, and about half that time at 5 °C (41 °F). Film liners or individual polyethylene head wraps are desirable for attaining high RH; however they should be perforated or be permeable to maintain a non-injurious atmosphere and to avoid 100% RH on removal from storage. Lettuce is easily damaged by freezing, so all parts of the storage room must be kept above the highest freezing point of lettuce of -0.2 °C (31.6 °F).

They follow up later in the document with this chart showing how lettuce's respiration rate increases with temperature—and of course, once harvested, the lettuce only has so many nutrients available to metabolize:

enter image description here

You can see at warmer temperatures, the lettuce will expire much more quickly.

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Usually sellers hold the lettuce at room temperature during the hours of sale (to show to buyers) and place them in the refrigerator in the night.

But attention. The supermarkets assemble the heads under plastic films (as said), which retain moisture, and daily keep them anyway in departments "fresh." The small vendors display the salads without protection, but often spray water, to maintain the freshness of the leaves, which otherwise would wilt.

The result is the same of cut flowers placed in a jar with water.

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+1, important to note that the lettuce in stores isn't actually left at room temperature for days. –  Jefromi Apr 17 '13 at 5:45
    
Having worked in a produce store I can tell you the practice of putting produce into a refrigerator at night is far from universal... Most stores have no storage other than what you see as a shopper. However it is treated during the day is how it is treated at night, possibly with a plastic sheet to cover. They count on the stock selling fast enough for it not to matter. –  SAJ14SAJ Apr 17 '13 at 19:30
    
@SAJ14SAJ, yes you have reason. But saying what should be done, we don't consider who does different, or maybe steals on the weight, or maybe intentionally fails to give change. We have to consider who acts correctly and honestly. I have found that a bakery close to home selling sweets in the package, where the expiry date had passed. I simply changed baker. –  violadaprile Apr 18 '13 at 15:17
    
@violadaprile I don't think their practices are intended to deceive or harm (I want to say the aren't disingenuous, but worried about the language barrier). Most retailers, especially small ones, simply have no storage outside of the retail floor, especially not refrigerated storage in quantities large enough to move the produce stock into it at night. Think of what that would do to their rent, utility bills, and therefore the cost of produce. –  SAJ14SAJ Apr 18 '13 at 15:34
    
Yes. In fact (here) most of selles have storages "under" retail floor with refrigeration (and yes, language barrier is an obstacle) :-). I see it almost always. And have a friend (when young we did any job) who worked 5-9 am to get legumes from storage, do package again and put them into shop. before it was opened to the public. So I so tend to think that the majority of retailers operate in this way. What is the correct one. Of course, I have not done a specific study and statistical, but personally I've never seen operate differently. –  violadaprile Apr 18 '13 at 16:22

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