The Science Behind Gluten and Odor Detection 

The most commonly asked question I get is: how many ppm (parts per million) of an odor can dogs smell? Well, the answer to that is not an easy one, and the truth is, it depends. My son is a Chemist, he has helped me do some very rough science with contaminating 50 lbs of mashed potatoes in my kitchen. All that really tell me is at what level Willow was able to detect in that substance, on that day, in that environment. If you change one element in that equation, the answer changes.  This page is dedicated to why that question cannot be answered at this time. ODOR Service Dogs Inc. is currently working on founding professional partnerships for the purpose of conducting studies in the area of gluten detection

Before even thinking about starting to teach a dog a target odor for any detection work, we first need an understanding of how the dogs' olfactory system works, how odor moves and changes, and all the other things that effect the dogs' ability to detect odor, such as wind, temperature, moisture content, other odors or in the air, etc. Is the odor high or low in comparison to the dogs nose? What materials may obstruct the dogs ability to smell? What distractions are in the environment?

PBS made a wonderful series explaining what a smell looks like:

Having reviewed what a smell looks like and how it behaves, we know odor is always moving and changing. Before we look at the dogs' olfactory system, we have to ask: how does the ever-changing and moving odor effect their ability to smell the target odor? Research has shown dogs can detect in parts per trillion in some cases, but not all cases. It all has to do with size of the target odor. Is the odor moist or dry? What direction is the wind blowing? Is a heater or air conditioner running in the room? Is a window open? How hot or cold is the environment? What currents are moving in the room or environment? For some answers to that, lets take a look at Search and Rescue to gather some information. My favorite explanation is by Hound and the Found:

Now that we know what a smell looks like, and the things that effect how odor moves in an environment, we need to understand the dogs' olfactory system. The canine nose contains hundreds of millions of sensory neurons, located in the olfactory. The olfactory acuity of the dog, which can detect odorant concentration levels at 1–2 parts per trillion, is roughly 10,000–100,000 times that of the human. This research shows us what a dog can detect in a sterile laboratory, with no outside distractions or odor interference, that are found in a real world situation that we discussed previously. 

Check out this article in journal The Royal Society by Craven et. al. 2009:

A simplified explanation is provided by Kathryn A. Bamford, Ph.D. K9 Officer, Massasauga Search & Rescue Team:

Figures from Craven et. al. 2009, The fluid dynamics of canine olfaction: unique nasal airflow patterns as an explanation of macrosmia

Lastly, we need to look at the size of the target odor we are going to train. From the above research, we know the size of the molecule determines how many parts per million (ppm) to parts per trillion (ppt) a dog is able to detect. For the target odor, we are going to look at gluten.

Gluten is actually made of two other proteins that, when water is added, combine to make the gluten molecule. Gluten is a large protein, and is a stable organic compound. It is heavy and sticky, which keeps it from lifting into the air, like an odor such as human breath which is used to train detector dogs for hypoglycemia. Human breath contains smaller molecules that include volatile organic compounds. From the research we have done so far, we know the heavier odor that does not lift into the air to disperse will drastically effect the outcome of the dogs' ability to detect. We also know, while gluten detection specifically has not officially been studied in a lab, we know that many factors will dictate from dog to dog and environment to environment whether a dog can detect gluten in ppm, ppb or ppt.

Some home studies have been done with gluten detection dogs by having my son, who is a Physical and Analytical Chemist, broke  down gluten by measuring milligrams of gluten to milligrams of neutral odor, for example:

0.10 mg gluten to 9.9 mg neutral odor = 100,000 ppm.

The gluten mixture needs to be broken down further from there, currently there is not yet laboratory machinery to detect below 5 ppm of gluten. The dogs are accurately detecting and indicating, in most environments, and some of the dogs have checked accurately at 1 ppm. 

It is never possible to say at any given time exactly how many parts per million of gluten a dog is detecting  as there are constantly changing factors at play. Until recently, there simply have not been enough trained gluten detection dogs to use to conduct a reliable research study for gluten detection.

Finally, what is gluten? Here is an article by Tuscany Diet:

The video below demonstrates why I never train gluten or any allergen in powdered form. Small lightweight particles can easily become airborne causing contamination to other training supplies

Gluten and Allergen Test  Elements Overview

The Science Behind Gluten and Odor Detection 
By: Dawn Scheu
Willow Service Dogs LLC
June 2017