Is It Kosher?
By Rabbi Eliezer Eidlitz — a comprehensive guide to the kosher status of hundreds of common foods, ingredients, and food categories.
Oils
In the last few decades, there has been a sharp worldwide decline in the use of animal oils. However, in the U.S. there has been an increase in lard and tallow (beef fat) use because it is cheaper and has superior shortening qualities.
The biggest problem for the kosher consumer occurs because oil processors produce both animal and vegetable oils on the same equipment. This is particularly problematic for hydrogenated (hardened) oils. Many vegetable oils are hydrogenated — the oil is first heated to 250°F in a vacuum (usually in the same equipment used for animal oils). A solid catalyst, which may be non-kosher based, is then added, and hydrogen gas is applied under pressure.
The exception is virgin or extra virgin olive oil, which is processed using a cold press method — never heated and not in contact with any non-kosher oils.
Most vegetable oils and products produced from them, such as margarine and shortening, cannot be relied on as kosher without strict rabbinic supervision.