Q: Why does my ketchup bottle say to refrigerate after opening? When I was a child, we used to keep the ketchup in the cupboard.
Good question! And it's not only ketchup. The same thing applies to soya sauce and a bunch of other items.
There are four possible reasons for the change. The first, and most cynical, is perhaps because manufacturers don't like to be sued. Warning you to keep the ketchup in the fridge is one way to prevent such problems. If you were to get sick with something that can be traced back to the ketchup and you didn't refrigerate it, the problem is yours, not theirs.
A second reason is that the preparation of many foods has changed. Because of the availability of refrigeration, it is possible to keep foods longer with lower levels of the preservatives. Pickles can be made with less salt and vinegar, which makes them taste less harsh and gives a nicer texture, but the trade-off is that they don't keep as well. That's why some brands of pickles tell you to always keep them refrigerated, even before the first time they are opened.
Which leads us to the third reason - consumer awareness and health. Reducing levels of some of the chemicals typically used to keep foods, such as salt, improves their healthfulness. With increased consumer attention to salt, sulphates, nitrates and other preservatives, which can now be found listed on food labels, consumers are demanding more healthy products. Products change to meet these demands.
And finally, regulation. Through various regulations and agencies, the government is responsible for maintaining a safe food supply. This has brought about dramatic changes in the way foods are prepared and handled. The instructor of the meat-cutting class which I took opined on the first day that we are handling food with such care, and reducing so many risks, that we may be killing off our tolerance to the occasional stray bug. Certainly, the way foods are stored and displayed in many countries varies hugely from what we are used to in North America. At the same time, allowable levels of those same chemicals, mentioned above, used to preserve foods have been reduced, as we learn more about their impact on the body.
All of these changes suggest that keeping your ketchup in the fridge is the best option for food safety.
So, because of the changes, for your own health, and since KitchenSavvy also doesn't like to be sued any more than anyone else does, always follow label directions.