Alcohol is forbidden because it intoxicates. The exact percentage of alcohol in a food or beverage has no effect on the ruling. The ruling applies to the food or beverage itself taken as a whole and not to its composition. Anyway, such small percentages of alcohol generally do not have any affect on a person who consumes the product.The only other possible objection that might be raised against such a product is that alcohol is considered an impure substance according to many scholars. However, it is an established principle in Islamic Law that minute quantities of an impurity that are completely submerged in pure substances do not make those pure substances impure. The quantity of alcohol in such a product is generally so minute as to be effectively non-existent as far as matters of purification are concerned.
The Prophet (peace be upon him) said: “Whatever intoxicates in large quantities, then a small quantity of it is forbidden.” [Sunan al-Tirmidhî (1865), Sunan Abî Dâwûd (3681), Sunan al-Nasâ’î (5607), Sunan Ibn Mâjah (3392), and Musnad Ahmad (5648)]
As long as the food or beverage in question does not intoxicate even when large quantities are consumed, then it is not prohibited.