To follow up on the storage of ketchup in particular, many items in cupboards and refrigerators have vinegar listed as a key ingredient. The first things that come to mind are hot sauce, mustard, ketchup. With respect to vinegar as a preservative, is there a rule of thumb in understanding the following:
- how does vinegar work as a preservative; is it solely by virtue of its acidic content?
- aside from the presence of sugars or artificial preservatives, is there a kind of ratio (or other metric) of foods containing, or whose base is, vinegar to know whether something needs to be refrigerated to keep from spoiling?
- what components can act to counteract vinegar's ability to preserve food?
- upon combination, can vinegar stabilize anything that otherwise would spoil? (If yes, you can answer generally, don't worry about a laundry list)
Note: This is asking not about specific jarring/pickling or other long term preservation methods, but rather to the on-use storage of food items in the kitchen and their ability to keep outside of refrigeration without spoiling.