Waste Management Engineering, Oklahoma Cooperative Extension Service


Making Sense of Smells

A Guide for Understanding Farmstead Odors

Part 1  The Physiology of Smell  Smell is a chemical sense.  Sensors wired to the olfactory and trigeminal nerves send signals to the brain where they are processed by the limbic system.

Part 2 Odor Structure  Humans have been buying and selling scents for centuries.  Perfume fragrances and farmstead odors are mixtures of notes.  Notes are made of odorants.  Odorants are odor causing chemicals.

Part 3 Odor Measurement  We can describe any smell by answering four questions: How does it smell? How long does it last? How much odor is present? How strong is it?

Part 4  Odor Concentration by Olfactometry  An olfactometer is an intstrument that delivers precise dilutions of odors to a panel.  The panel decides when it can no longer smell the odor (dilution to threshold), the inverse of this is the odor concentration of the sample in OUs. 

Part 5  Odor Intensity and Offensiveness by Olfactometry  Olfactometry panels determine how strong and how bad they perceive an odor to be.

Part 6 Simulated Olfactometry Exercise  Students gain understanding of  the complicated science of olfactometry through a simple sniff test.

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