The answer given to the foregoing question by Ayatollah Mahdi Hadavi Tehrani (may Allah grant him long life) is as under:
If gelatin is derived from vegetable for an animal which has been slaughtered according to Islamic law, it is halal and ritually pure. If it is likely to have been derived from halal source, it will be pure and if it is probable that it has been derived from vegetable it would be also halal to eat.
If a chemical change occurs in the original ingredients during the process of manufacturing the gelatin, it is clean and there is no problem at all in eating it even if the original ingredient may have been pork or meat of an animal which has not been slaughtered according to Islamic laws.
Alcohol is pure but it is not permissible to consume it. In case the amount of alcohol existing in food is so minute that the food is considered by the wise as having no alcohol, it is halal to eat. In case one doubts about it, it is treated as permissible to eat.