Ultimately, temperatures that are at around -7 º C (for at least several hours) will freeze the water crystals in the grapes. This is when the grapes must be harvested and pressed. In the press, the water remains as clumps of ice while only the concentrated must flows out. Eisweins are recognised by their elegant, piquant fruit and racy acidity. Plus the varietal character is still clearly present as well. The youngest of the Prädikatswein group are Strohwein and Schilfwein. However, their method of production actually has been known since Roman times: Ripe, unbotrytised grapes are air-dried on mats of straw or reeds for three months, and then pressed and fermented. Taste-wise, these wines are usually in between that of a botrytised wine and an Eiswein. Also, they show elegant fruit, but generally low acidity.