Seems odd that it should be thought of as disgusting, unless perhaps it's being associated with being excessively drunk.
It's just a natural release of gas pressure which can occur for many reasons, mostly as a direct result of your body digesting food.
Some food combinations and the overall state of health of a person can affect whether it happens or not.
I have heard that in some cultures, burping after being served a meal is actually taken as a compliment indicating that the food was enjoyable.
It is possible to consciously hold the gas in, so burping is not 'required', although doing so might be uncomfortable.