Whether accidentally or as a matter of necessity, sometimes alcohol gets left in the car. While this isn’t much of an issue during cold weather months (unless we’re talking sub-zero temps and frozen beers), when it’s warm outside, leaving that 6-pack or bottle of wine to cook in the car is definitely something you want to avoid.
Generally speaking (because I’m no scientist), the less time you leave alcohol in a hot car, the better. This is especially true for beer and sparkling wine, which can explode if left in the heat for too long. Extreme heat, coupled with direct sunlight, can also diminish the quality and/or flavor of the booze in question (like skunked beer). Still wines can also get tainted from being left in a hot environment for too long. And while spirits won’t be as affected as beer or wine if left in a hot car for a short period of time, it’s probably best to avoid forgetting that bottle of bourbon or tequila in the trunk for a few weeks or months to preserve its quality and flavor (plus, don’t you want to drink it?!).
In short, you can keep spirits in a hot car longer than you can wine and beer, but you probably want to steer clear of leaving any alcohol in the heat and/or direct sunlight for more than a few hours.
