How to tell if pickles/cucumbers have gone bad

There is a lot of variability in how fast milk will go bad.

• How long the milk has been opened
• Pasteurized vs ultra-pasteurized
• Temperature the milk is kept at
• Thermal cycling: how long and how often is it kept above 40º
• Where in the fridge it is kept. The door will have more thermal cycling than a shelf, higher shelves tend to be warmer than lower ones.

All of these influence how long milk stays good. The big date on the top is used by grocers to determine when it can't be sold. If you look closer there will be text to the effect of, "Use within 7 days after opening". This isn't a guarantee. Leaving the carton out while you cook will allow it to go bad faster, as will keeping it in the door. Also if your fridge is too warm for some reason, things will spoil faster.

Traditional fermented pickles were kept in barrels, but they're not the kind that you buy in a big jar at Costco. Those pickles have been briefly cooked in a brine, and should be refrigerated after you open the jar. The salt and vinegar should keep them safe for a while, but they will likely go bad at room temperature before you finish eating the whole jar.

As an anecdotal note, an office I used to work in kept one of these large jars of pickles around. After being open for a few years, they were clearly spoiled, and nobody would touch them.