The northerly winemaking regions of Germany straddle the 50th parallel and are amongst the world’s coolest vineyards.
Nonetheless, vine cultivation dates to the ancient world—wild vines had been growing on the upper Rhine previously, but Vitis vinifera arrived in Germany with the Romans. Near the end of the 3rd century, Emperor Probus overturned Domitian’s 92 CE ban on new vineyard plantings, and viticulture followed the Romans into provinces north of the Alps. By the fourth century winemaking was definitively established along the steep slopes of the Mosel River. Charlemagne, the legendary beard-stained lover of wine—whose newly minted Carolingian calendar replaced the Roman October with Windume-Manoth, “the month of the vintage”—introduced vine cultivation east of the Rhine River in the late eighth century. During the Middle Ages, the Church was instrumental in shepherding the development of vineyards, and many of Germany’s modern einzellagen (vineyards) owe their nomenclature to monastic influence. As in France, the Church essentially operated its own feudal economy: it collected a tithe, or tax, from the parishioners who worked the vineyards, and wine made a suitable substitute for cash. The Cistercians of Burgundy founded the famous Kloster Eberbach monastery in the Rheingau in 1136, where they amassed the largest vineyard holdings in Europe by the end of the Middle Ages, with over 700 acres of vines. The walled Steinberg vineyard, an ortsteil within the commune of Hattenheim, was the monks’ centerpiece and remains wholly intact today—an alleinbesitz (monopole) of Kloster Eberbach for over eight centuries
Nick Davis I posed your question to the German Wine Institute, and Michael Schemmel had this to say:
"The term 'Ortsteil' does not have a siginificance in terms of wine growing. It literally means 'borough.' You mentioned Schloss Johannisberg. Usually you would find the term 'Ortsteil' in the offical address of the estate e.g. Geisenheim Ortsteil Johannisberg. Here this means that the estate is located in Johannisberg which is a borough of Geisenheim."
That should clear that up, and some of the earlier confusion about Schloss Johannisberg too.