Balancing flavors, for me is not layering flavors, nor is it umami, or acidity. Balancing flavors is the act of combining complimentary ingredients that that the whole is greater than the individual parts. A perfect example of this is when I make my pineapple sweet and sour sauce. It contains a mixture of pineapple, brown sugar, vinegar, onion, chicken, salt, soy sauce, ginger, and 5-powder. Each of those ingredients can overpower the sauce. Too little of any of them will leave the sauce flat. But added in the right amounts, they come together to make a very tasty sweet and sour sauce.
Another example is making hot fudge sauce. For me, ideally, hot fudge is darker in flavor than is milk chocolate, less dark than semi-sweet chocolate. It is enriched by the sweetness of milk, without being runny, and has just a hint of salt added to intensify the chocolate flavor.
Salt is probably the most important seasoning you can use. Again, it can quickly overpower a dish. Try eating your favorite savory foods with no salt. They become rather bland.
Acids balance with sweet things. Think of a good rhubarb jelly. It is a combination of the very sour rhubarb, and sugar, combined sometimes with the spicy flavor of cinnamon. The sugar makes the acidic rhubarb more palatable, and the rhubarb cuts the sour flavor of the sugar. If one or the other is too strong, the flavor is unbalanced, and not as flavorful as it could be.
Unfortunately, balance can't be taught. It has to be experienced. Some herbs and spices work together, and some don't. The same is true with salt and sweet. I have a friend who loves to put salt on his ice cream. For the way his taste buds and brain work together, the flavor combination is wonderful. For me, I don't like salt on my ice cream.
Fortunately, most of our tastes are similar. I'm pretty confident that I can season my pasta sauce so that most people will really like it, though my DW's hyper-sensitive tongue doesn't do well with the amount of basil I like to use. Basil has some of the same chemical flavor compounds as does black pepper. She is hyper sensitive to those compounds, and so doesn't enjoy basil, my favorite herb.
To sumarise, balance, as pertains to food, is that act of adding complimentary flavors where none dominate, but all add to the quality of the dish.
That's my opinion, humble opinion.
Seeeeeya; Chief Longwind of the North
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