Suitability of a region for wine-growing which can be measured by objective criteria. Important criteria are climate and weather, which are of eminent importance for the flourishing of the vines during the vegetation cycle. The exposure (direction of sunlight) or orientation of the vine rows plays an extremely important role, whereby a slope with a corresponding inclination further enhances the effect. In dry areas with favourable thermal conditions, south-east to east slopes are ideal, while south-west exposure is optimal in climatic border areas with thermal deficits but sufficient precipitation. According to research in Geisenheim, the optimal temperature for vine growth is between 25 and 28 °C. Towards the end of the ripening period, it should be between 15 and 20 °C in order to achieve optimum physiological ripeness of the grapes. Sunny days alternating with cooler nights are advantageous with regard to the balance of sugar and acidity. Shortly before the grape harvest, heavy rainfall is undesirable due to the risk of dilution.