You will never see a DUI case where the officer does not report an odor of alcohol on the suspect’s breath. Never. The officer expects to smell it and it is a psychological fact that we see, hear and smell what we expect to see, hear and smell.
In fact, most police DUI reports are formatted for the usual symptoms: there will be a box for "odor of alcohol", which the officer checks off. There are often three boxes, labelled "strong", "moderate" and "weak"; there is no box for "none", so that is not an option for the officer. The "strong" box is almost always checked. Presumably, the stronger the odor of alcohol, the more intoxicated the person arrested.
There is only one problem with this: Alcohol has no odor. Assuming the officer actually does smell an odor on the breath, what he is smelling is not ethyl alcohol but the flavoring in the beverage. And the flavoring can be deceptive as to the strength or amount consumed. Beer and wine, for example, are the least intoxicating drinks but will cause the strongest odor. A much stronger drink, such as scotch, will have a weaker odor. And vodka leaves virtually no odor at all.
Consider a simple experiment. Have a friend drink a can of "near beer" — the stuff that looks, smells and tastes like beer but has no alcohol in it. Then smell his breath. You will smell an "odor of alcohol" — and maybe a strong one.And, of course, there can be any number of causes of an "odor of alcohol" on a person’s breath: mouth wash, throat spray, cough syrup. Illness, indigestion or simple bad breath has been the cause of more than one officer’s trigger-quick conclusion that the suspect has an "odor of alcohol on his breath".
The point of all this is that the odor of alcohol has very little relevence in a drunk driving case. It may or may not indicate that the person has consumed alcohol. It absolutely has no evidentiary value on the much more important question of how much the person has consumed — or what he had to drink, or when. Depending upon circumstances, a person with a single drink can have a "strong odor of alcohol on his breath", and an extremely inebriated person can have a "weak" odor. And an experienced and honest DUI officer will readily admit this….if he is ever asked.
Unfortunately, the odor of alcohol on a person’s breath may have a greater impact on a DUI case than any other single factor. This is because most officers who pull a driver over for some driving irregularity at night are looking for further signs of drunk driving. When the officer approaches the driver’s window and smells alcohol, that confirms his suspicions. Since few can pass the "field sobriety tests", particularly under the conditons in which they are given, an arrest is likely.