Shrubs are classically refreshing fruit and vinegar-based syrups that were sweetened and diluted to make a beverage since revolutionary times. Bittermens decided to make a hot pepper shrub, fortified it with alcohol (to better extract the flavors from the spices) and made it much more concentrated, so you only need to use drops instead of ounces to get the desired effect… which, in this case, is a nice amount of heat.
