Gwahaju is a type of Korean rice wine that is fortified (honyangju) with soju. This drink was traditionally enjoyed in the summer, and it originated as a preservation technique. At the time, there was no refrigeration and during warm summer months, rice wine would often go bad.
As soju is a distillate, adding it to the rice wine increases alcohol content, and the wine does not spoil if the temperature rises. This is why gwahaju was mostly associated with summer. It is often dubbed as a Korean summer wine. The drink has many variations, including several popular regional styles that include additional ingredients, such as fruit or botanicals.