In shopping, you should be aware that you may find meat, fish, and egg products mixed in with other foods, so be sure to study labels carefully. For instance, some brands of yogurt and sour cream contain gelatin, which is prepared from the horns, hooves, and bones of slaughtered animals. Make sure any cheese you purchase is rennetless, because rennet is an enzyme extracted from the stomach tissues of calves. You should also avoid foods precooked by people who are not devotees of Krishna. According to the subtle laws of nature, the cook acts upon the food not only physically, but mentally as well.
Food thus becomes and agency for subtle influences on our consciousness.
To give another example of this principle, a painting is not simply a collection of strokes on a canvas. It is also an expression of the artist's state of mind, and this mental content is absorbed by the person who looks at the painting. As far as possible, use only fresh, natural ingredients. In preparing food, cleanliness is the most important principle. Nothing impure should be offered to God, So keep your kitchen work-area very clean.