By smelling we contaminate the food or any substance that we offer to The Lord. It's for this same reason we are not supposed to smell the flowers or the incense before offering.

After offering of course it is transcendental and we can pass on the flowers to be smelled by devotees.

Sankhya:

Metallic objects are cleaned by earth(sand/clay)

Wollen cloth is cleaned by simply drying up in the air

Body is purified by taking bath.Mind/Soul is purified by Mantra/chanting the Holy names of The Lord.

Rain water is purified by stagnation for 10 days.

Large water bodies such as rivers or running Water are not contaminated.

Small water bodies or ponds are contaminated by regular usage.

Earthen pots and few other objects covered by dirt are purified over a period of time when exposed to sunlight.

Usually objects that are made of earth are cleaned by water or air.

All purification happens over a period of time and so time is also a major factor in the purification process.

By thinking of The Lord constantly, the mind and soul can be kept pure always.

Don't ever smell the food you cook for offering