Fresh fruits, vegetables and grains are, in their natural unprocessed state, kosher and pareve. They do not need kashrut certification and can be used with either dairy or meat. However, once a vegetable is combined with a dairy or meat product, it becomes dairy or meat respectively.

Processed vegetables such as those canned or frozen may pose a problem. They are sometimes creamed and may contain non­kosher, dairy or meat ingredients; or they may have been processed in vessels used for meat, dairy, or even non-kosher products.

A more common problem with vegetables involves possible insect infestation. The prohibition against consuming insects, even very tiny ones — as long as they are visible to the naked eye — is mentioned five times in the Torah and is very strict. In recent years, due to federal regulations restricting insecticide spraying and genetic changes causing some insects to become more resistant to the insecticides, there are increasing amounts of insects such as thrips and aphids infesting some vegetables, especially green and leafy varieties. Although quite small, they are visible to the naked eye and must be removed. Aphids range in size from 2 -5 millimeters (1/16 - 1/8 of an inch).

Many vegetables, fruits, nuts, and grains must be checked before cooking or eating for the presence of small insects. Packages of pasta are also occasionally infested. Some particularly severe problem vegetables are artichokes, asparagus, brussel sprouts, cauliflower, and leafy vegetables.

The method of checking depends on the vegetables. Leafy vegetables such as cabbage and lettuce should be checked leaf by leaf. Washing under running water or soaking in salt water is helpful, but the vegetables must also be inspected under a bright light, either daylight or artificial light. Certain vegetables, such as celery and zucchini may be used after they are washed under running water and scrubbed with a vegetable brush.

The degree to which insects are present varies according to the region, season, and origin of the produce. If it is known that a certain variety is infested, either avoid it for that season or examine it very carefully to remove all insects.