Mouth alcohol is real, but it is narrower than the internet suggests. Alcohol left in the mouth from a drink, mouthwash, or breath spray can raise a breath reading for a short time. Officers are trained to wait before taking a sample for that reason. Whether that happened in your case is a question of fact, usually answered by video. This page is part of our Montana DUI Guide.
What Mouth Alcohol Is
An evidentiary breath test is meant to analyze deep lung air. Montana's rules define breath as "that portion of the exhaled deep lung air that is collected for alcohol analysis" (ARM 23.4.201(7)). Alcohol in that air reflects alcohol in the body.
Alcohol in the mouth does not. The NHTSA manual used to train officers in DUI detection explains: after a person takes a drink, some alcohol remains in the mouth, and if the person exhales soon afterward the sample "will contain an additional amount of alcohol and the test result will be higher than the true BAC." The manual adds that it "takes approximately 15 minutes for the residual alcohol to be eliminated from the mouth."
Common Sources, and What Each One Means
| Source | What the sources say | Why it matters |
|---|---|---|
| Mouthwash, breath spray, cough syrup | NHTSA's officer manual says most of these contain alcohol and may produce residual mouth alcohol. | Matters only if used shortly before a breath sample. |
| A recent drink | Some alcohol remains in the mouth. NHTSA says it takes approximately 15 minutes to be eliminated. | Most relevant to the roadside test. |
| Kombucha | The federal alcohol bureau (TTB) says fermentation can push some kombucha to 0.5 percent alcohol or more. | A small amount of real alcohol, so it is a drink, not a false reading. |
| Non-alcoholic beer | A malt beverage may be labeled non-alcoholic if it contains less than 0.5 percent alcohol (27 CFR 7.65). | Same point: little alcohol, but some, unless labeled alcohol free. |
| Burping or regurgitation | Raised in Montana cases as a way alcohol from the stomach could reach the mouth. | Courts have looked for evidence that it actually happened. |
The same manual notes that ordinary characteristics of breath, such as bad breath and food odors, do not affect accuracy.
What Montana's Rules Require Today
This is where many articles go wrong. The Administrative Rules of Montana that govern breath testing (ARM 23.4.201 to 23.4.225) do not state a 15 or 20 minute observation or deprivation period in their text. What they require is that:
- the instrument be a model approved by the Forensic Science Division (ARM 23.4.209);
- the operator be certified (MCA § 61-8-1018(1)(b)(i));
- the instrument be field certified at least every 31 days (ARM 23.4.213(1)); and
- "all breath analyses must be performed in accordance with the procedures set forth by the Forensic Science Division" (ARM 23.4.201(25)).
Any waiting period comes from the division's procedures and from the checklist printed on the breath analysis report form, not from the text of the rule. We have not been able to read the division's current procedure document, so we do not quote it here. Your own breath record shows the checklist the operator signed. See breath test procedure and the observation period.
How Montana Courts Have Handled It
Two Montana Supreme Court decisions frame the issue.
State v. Flaherty, 2005 MT 122.The driver argued he was not watched closely for 15 minutes before an Intoxilyzer 5000 test. The Court explained that the checklist then in use required that "no oral ingestion of any material" occur in the 15 minutes before testing and that the person be observed during sample delivery, not that an officer stare at the person the entire time (¶¶ 14 to 15). The result was admitted.
State v. Levanger, 2015 MT 83.A trooper found chewing tobacco in the driver's mouth during transport, had him spit it out, and tested him 20 minutes later on an Intoxilyzer 8000. The Court said the checklist "recommends" no oral intake for 20 minutes, that older versions of the rule required compliance with the checklist, and that the version then in effect did not (¶¶ 4, 11 to 12). It upheld the result because the evidence showed the trooper followed the checklist anyway.
ARM 23.4.212 was amended in 2023 and 2024, and the sentence the Court relied on still reads the same way. The practical lesson is that courts look at what the record shows actually happened in the minutes before the test.
Burping, Belching, and Regurgitation
The theory is that alcohol from the stomach reaches the mouth and contaminates the sample. In both cases above the drivers raised it, and in neither did the Court find evidence that it occurred. Levanger called the argument "a hypothetical without any factual basis" (¶ 14). If it did happen, the station video is the evidence. For conditions that make it more likely, see medical conditions and breath tests.
The Roadside Test and the Station Test
The handheld roadside device is often used within minutes of the stop, which is when mouth alcohol from a last drink or a breath spray is most likely to be present. NHTSA's manual addresses mouth alcohol in its section on those preliminary devices. In Montana that test is a screening step, and its result is recorded only as positive or negative (ARM 23.4.225(5)). See the roadside breath test.
The station test comes later, after an arrest and a drive, which by itself usually lets a waiting period run. That is why a mouth alcohol argument against a station result needs specific facts.
What to Look At in Your Case
- The video. From the stop through the sample. Did you put anything in your mouth, vomit, or visibly burp?
- The breath record. The times printed on it, and the checklist the operator completed.
- The certification records. See the breath test machine.
- Your request. Full information about the test must be made available to you or your attorney on request (MCA § 61-8-1019(3)).
If the record shows a real problem, it becomes part of challenging the breath test. If it does not, an honest lawyer will tell you so and look at the rest of the case.
This page explains Montana law in general as of the 2025 Montana Code Annotated and the Administrative Rules of Montana. Statements about alcohol in the mouth come from NHTSA's DWI Detection and Standardized Field Sobriety Testing participant manual. It is not legal advice about your specific case.