On the small municipality of Andlau there are three Grands Crus clustered together: Wiebelsberg, Moenchberg and Kastelberg which is the smallest in surface area, with 5.82 ha.
As often in Alsace, the concentration of multiple factors in a confined area plays a fundamental role. Here the terroir is not only very exposed to the sun but it also sits on a steep slope with the incline reaching up to 45° in some places. Producers have overcome these steep slopes by building many small terraces supported by dry stone walls.
The terroir has nearly-perfect geological unity. It sits on shale having evolved through metamorphism in a very hard rock, providing very pebbly and porous soil. The slivers of shale rock allow for deep root systems which is perfect for normal vitality even in drought years. Dating from the Silurian period, this geological formation is among the oldest around. The rock is made of quartz, mica and chlorite.
In the upper part of Kastelberg there are some outcrops of granite and the soil at the bottom of the hill is a little richer with a gentler slope.
Here the Vosges and Rhineland faults are intermingled and the Kastelberg vineyard is directly located on the base of the Andlau valley outlet on the Alsace plain.
It is protected from fresh ocean winds by the Champ du Feu massif and from the north winds by the Crax mountain. The extremely steep slope faces south/south-east, allowing it to have a maximum of sunshine. Moreover, its dark Steige-shale earth heats up well, especially in the spring.
The varietal which feels the most at home and which expresses itself fully is the Riesling.