It's decided by a key stage during the vinification of red wine: maceration.

其实，葡萄酒的颜色是由酿造过程中的一个关键阶段——浸皮决定的。

youdao

Vinification: Classic vinification. Matured in vat with inert gas. Bottled in our cellars.

酿造：传统的酿造过程。在生产酒庄酿制并且罐装。

youdao

VINIFICATION PROCESS : Traditional without bunch of grapes for 4 weeks under controlled temperatures. Storage in tank and oak barrel before bottling.

发酵过程：传统的发酵方法，去除葡萄梗后在温度控制下发酵4个星期。装瓶之前存放在橡木桶中。

youdao

Vinification, or winemaking, is deeply ingrained in the culture of this ancient Christian country, perched in the mountains of the Caucasus.

CNN: Unearthing Georgia's wine heritage