Having trouble with the sweet & sour sauce recipe
5% is the acid content of most common vinegars, and if a recipe doesn't explicitly state to use a stronger one, assume a 5% type is intended. There seem to be versions of white distilled vinegar in both 5% and 10%, an even stronger version called Essigessenz at 25% (!!!) is common in Germany. You likely bought the 9% version by accident, you should dilute it 1:1 with water or only use half the amount.