Flavor – What’s the point of using sugar in savory dishes

The sugar is mostly just for flavor. I use sugar when making pickled beets and eggs, but don't use it in my dill pickles or pickled peppers and onions. It just depends on if you are trying for a sour, sweet and sour, or sweet pickle (note that there is no vinegar in many fruit pickles).

Before you decide to run off and leave out the vinegar, however, I would note that for pickling safety purposes there has to be enough acid to keep botulism causing bacteria from forming and peppers are a low acid vegetable. If you wanted to eliminate the vinegar, you'd have to move to pressure canning.

Sugar does not cause sour food to be any less acidic. The difference is purely one of perception; we are wired by evolution to prefer sweet tastes and tend to perceive less of other tastes when a high sugar concentration is present.

Sugar does not ionize - it is not basic or acidic. Acidity itself is a chemical property, and only a base (such as baking soda or trisodium citrate) can actually neutralize it. Two other compounds - miraculin and curculin - actually alter our mouth chemistry and really do cause sour foods to taste sweet, without actually sweetening the food itself. But plain sugar does nothing at all - there is no chemical reaction happening. It's just masking other tastes, not neutralizing them.

The reason sugar doesn't mask bitterness as effectively as sourness is that sweet and sour have roughly similar taste thresholds, while most humans are extremely sensitive to bitter tastes. We can detect quinine (the reference solute for bitterness) in solution at 0.5 ppm, whereas sucrose isn't normally detectable at levels below 5000 ppm. The amount of sugar needed to mask a significant bitter taste is simply not practical.

If you want to neutralize a bitter taste, use salt instead.