As an expert sommelier and brewer, I can tell you that the flammability of alcohol is determined by its alcohol by volume (ABV) or proof. Generally, any alcohol listed above 100 proof or 50 percent ABV is considered flammable. This means that it has a high enough alcohol content to easily catch fire and burn.
The concept of proof actually originated from the British navy in the 18th century. Gunpowder was used to test the alcohol content of spirits. If the gunpowder would still ignite when soaked in the alcohol, it was considered “proof” that the spirit was of sufficient strength. Hence, the term “proof” was born.
However, it is important to note that today, proof is primarily used for labeling alcohol content in liquors for consumer safety and for taxable purposes. It is no longer directly related to the flammability of the alcohol.
In terms of practicality, any alcohol with a high enough ABV can be flammable. For example, I have personally experienced the flammability of high-proof spirits while working in a bar. We would sometimes use high-proof rum to create a spectacular flaming cocktail. The alcohol content of the rum was around 151 proof or 75.5 percent ABV, making it highly flammable. It would easily catch fire when ignited, creating a visually stunning effect for the customers.
It's worth noting that when it comes to flammability, the alcohol content is the key factor. Other factors such as sugar content or additives may influence the behavior of the flame, but they do not determine whether the alcohol will burn or not.
To summarize, any alcohol listed above 100 proof or 50 percent ABV is straight up flammable and would therefore not hinder the ability of gunpowder to fire. However, it's important to remember that proof is primarily used for labeling purposes, and the flammability of alcohol is determined by its alcohol content. So, be cautious when handling high-proof spirits and always prioritize safety.