Q. Why can’t I simply read the ingredients of a product to determine if it’s kosher?
In addition there are detailed kashrut rules that non-experts do not always know, such as how the product was manufactured and whether a small percentage of a normally prohibited ingredient can be regarded as nullified.
Manufacturers and distributors themselves may be unaware of the precise ingredients. Recipes and methods of manufacture can be changed without notice and sometimes when a particular substance is unavailable an unacceptable substitute is utilised without changing the labels or informing the public.
In communities which have a professional kashrut checking system it is best to rely on them, and if their published lists do not contain the product you are interested in you can and should ask them for advice.