Phil Price, a nationally known DUI attorney in Montgomery, Alabama, conducted an interesting series of tests a few years ago on one of the most commonly used breath testing machines. Without consuming any alcoholic beverages, he submitted himself to repeated breath testing — after eating various types of food.

His findings were startling.

After consuming almost any type of bread product — white loaf bread, donuts, pretzels, pastries, etc. — Price consistently registered blood-alcohol readings on the machine. These levels were commonly around .03%, but rose as high as .05% (enough, along with a drink or two, to reach illegal levels). Further, the Intoxilyzer’s slope detector (an electrical circuit designed to detect alcohol from the mouth rather than from the lungs) failed to indicate the presence of any “mouth alcohol”. He reported this in an article entitled “Intoxilyzer: A Bread Testing Device?”, 15(4)Drinking/Driving Law Letter 52.

Reacting to the use of this article by defense attorneys in their state, the Washington State Toxicology Laboratory conducted their own studies to refute the findings — this time with the machine used in Washington, a DataMaster. Unfortunately, their research only confimed Price’s experience.

As reported in Logan and Distefano, “Ethanol Content of Various Foods and Soft Drinks and their Potential for Interference with a Breath-Alcohol Test”, 22 Journal of Analytical Toxicology 18 (1998), a variety of breads and soft drinks were tested and found to contain no alcohol. Alcohol-free subjects then ingested these products and provided breath samples into a DataMaster. The law enforcement researchers’ conclusions:

We found that, particularly at low concentrations but as high as 0.046g/210L, mouth alcohol rather than expiratory breath alcohol may be reported as apparent true breath alcohol…

In other words, alcohol-free subjects who consumed bread or soft drinks were causing the machines to read up to .05% blood alcohol concentrations (readings are rounded off to closest 1/100th percentile). Furthermore, the slope detection system failed to screen the effects of mouth alcohol from that of alcohol coming from the lungs:

It is evident from these results that the slope detector feature was unable to distinguish mouth-alcohol concentrations at these very low levels.

What caused bread to register on breath machines as alcohol? The theory of the state lab’s experts:

Most baked products with listed contents indicating they contained yeast did in fact have some alcohol present. Alcohol is produced by the fermentation process in yeasts by their action on simple sugars used in preparing the dough….Although most of the alcohol in the dough is lost during the baking process, some is evidently retained in the matrix of the bread…

Parenthetically, there exists additional scientific literature reporting intoxication in animals eating dough and sourdough. Suter, “Presumed Ethanol Intoxication in Sheep Dogs Fed Uncooked Pizza Dough”, 69(1) Australian Veterinary Journal 20 (1990); Thrall, et al., “Ethanol Toxicosis Secondary to Sourdough Ingestion in a Dog”, 184(12) Journal of American Veterinary Medical Association 1513 (1984).

The effects of bread on breathalyzers is not just an interesting anecdote. The significance of these findings should be apparent. First, bread dough tends to stick between the teeth and remain there for extended periods of time, later to be breathed into a breathalyzer; it also absorbs alcohol while between the teeth. Second, although it is not illegal to drive with a .04% blood alcohol level,adding one or two drinks to the bread reading could raise that above the illegal .08% level.