How do the police prove a person consumed alcohol if no breathalyzer or blood tests were given showing alcohol in his system?

Actually, recent case law makes the use of aPreliminary Breath Test device irrelevant in most jurisdictions.

You raise good questions, but each of the issues you raise can be categorized as a defense, rather than an issue of proof. The officer will likely testify to the common signs of intoxication, and if he says these magic words, "I detected the odor of an alcoholic beverage emitting from his breath and person" any defense as to spillage, etc can go out the window.

This phrase is so common it becomes repetetive and expected. The Commonwealth is required to prove guilt beyond a reasonable doubt. That does not require "concrete proof." The officer's well-rehearsed testimony will likely be sufficient to establish guilt . And, as much as we would like to think that a defendant has an absolute right not to testify, in cases like this, it would be highly unusual for an MDJ to find your son not guilty unless he takes the stand to testify, credibly, that he did not consume alcohol.

Obviously, a primary concern in cases like this is the license suspension. Assuming you son has no prior record, the officer may be willing to amend the citation to disorderly conduct or public drunkenness. In either case, your son would not lose his license. Moreover, the conviction can be expunged in 5 years.