You can make sour gummy bears by adding 1/4 of a teaspoon of citric acid into the mixture once the mixture is smooth and fluid and after I have microwaved the gelatin. Add this citric acid by pouring it into the mixture and whisking the mixture until the citric acid is blended in properly. Taste it to see if it is sour enough for you and if it is not, I advise that you add a maximum of another one-fourth of a teaspoon of citric acid.