It is these southern mountains that provide for the variety in microclimates and soil types. To the west the sandy soils of Bilogora, in the middle the lime and chalk of Papuk, and to the east the alluvial soils overlying a volcanic base. Indeed it is on Krndija that you can find the oldest rocks in Croatia, dating back some 300 million years, well before the Pannonian Sea was formed and then dried out. The well drained slopes of the foothills have been used for viticulture since at least the Roman times.
Click on image for large scale map - Image credit: Virovitica-Podravina County Tourist Board
As can be seen from the map, the main winemaking centers are along the edge of the mountains. Orahovica, Slatina, Suhopolje, Virovitica and Vukoslavljevica. The very largest wine producer is PP Orahovica. They grow grapes at ten different locations on the slopes of Papuk and Krndija. Vineda Cellars from Vukosavljevica, and Diba d.o.o. from from Suhopolje are other well known producers. Most towns and larger villages have a vintners association and there are numerous small winemakers. In Orahovica you can even taste quality wines produced by the high school "Stjepan Ivšić".
Slatina has the distinction of being the location where the first sparkling wine was produced in Croatia, by Count Schaumburg-Lippe in 1964. Sadly he stopped making it in 1912. The local history museum is worth a visit.
The two major annual agricultural events are the international agricultural exhibition Viroexpo in late February, which this year had over 750 exhibitors from 27 countries, and the Agroexpo fair in late August or early September (this year on September 4th). The top number of gold medals at Viroexpo 2016 was taken by Vineda Cellars, whose wines you can try in Vukosavljevica.
Orahovica hosts the annual Wine and Kulen Fair in late June every year. Part of the fair is a "Wine Marathon" race, where contestants have to race 8.5km, visiting thirteen wine cellars and tasting three wines in each. Assuming anyone actually finishes, prizes are awarded for various "interesting" categories. Kulen is the famous Slavonian cured meat product, a relative of salami, that is hard to describe but delicious to eat. While in Orahovica, visiting the old PP Orahovica wine cellar is a must, and a hike up to Ružica fort will not only burn up some of the extra calories, but provide for some fabulous views. As legend has it Ružica was the most beautiful of the local fairies who were preventing the castle from being built. The Count managed to trap her, imprison her between the walls and finish his castle. But it was cursed as a result of his treatment of Ružica, and it collapsed the day after it was finished. Even today, a thousand years later, the town has roses growing everywhere in memory of the lovely Ružica.
Most towns and villages will also celebrate St Martin's (Martinje) on November 11th when the new fermenting grape juice is "officially" renamed into wine, and St Vincent's (Vincekovo) on January 22nd when dormant grapevines are decorated with food and watered with wine to ensure a good harvest. Both feasts involve much eating, drinking and celebrating.
The County Tourist Board has a nice online brochure (requires Flash)