Plenty of wineries around Stuttgart - quite off the beaten track in terms of what's well known internationally, but they like to say that the reason for them being relatively unknown is that they sell most of their wine to locals. The terroir is quite special, and the wines are as well - Trollinger red (which is "Schiava" in Italy or "Vernatsch" in Tyrol) might be a bit of an acquired taste, more so if you're accustomed to what Germans call "new world" wines (US, Australia, South Africa, NZ, Chile).

Put "Weiprobe weingut Baden-württemberg" into Google and see what comes up along your route. There are some big estates (the Duke of Wurttemberg's winery is one of the big traditional places - www.weingut-wuerttemberg.de), but most are co-operative or family-run traditional affairs. In fact, the City of Stuttgart itself owns and operates a winery (www.weingutstuttgart.de) which owns some of the most famous vineyards along River Neckar (Cannstatter Zuckerle happens to be entirely within Stuttgart city limits).

Many of the small wineries have currently closed their cellar door outlets because of Covid, but near Stuttgart Dolde (Dolde Wein: Dolde Wein) appear to be open again on Saturday mornings. Better check beforehand if they're actually open, an what type of service they're offering at the moment.

ETA re car rental: catch a train to Stuttgart and pick up the car there. If you go on Friday, make sure you book well in advance and with reserved seats, Friday evening is peak hour for long-dinstance trains leaving Munich.