冬季釀酒葡萄酸度偏高之生理探討

Abstract

台灣冬天旱季生產的葡萄不但糖度高，香氣濃，病害少，具有許多超越夏季葡萄的優點，同時冬季低溫比夏季更適合葡萄酒的釀造。近年來雖有釀酒葡萄產期調整到冬季之議，但由於冬季葡萄酸度過高，且經多年之調查仍不明其原因，因此遲遲不能推展。 本研究針對上述冬季葡萄酸度過高的問題，比較分析冬季與夏季葡萄，單粒果實內酒石酸與蘋果酸變化的差異，探討冬季葡萄酸度偏高的生理原因。 酒石酸與蘋果酸形成與消失的曲線，在冬夏兩季並無顯著不同，差異僅在夏季葡萄蘋果酸含量下降幅度較大，成熟末期幾乎可能完成被分解，冬季果實則分解到某一個程度，含量不再下降。 分析葡萄果實蘋果酸的分解消耗量，與硬核期後累積溫度的關係，不論是金香或黑后品種，皆呈極顯著的負相關。蘋果酸主要經由呼吸作用消耗，由於夏季溫度高，呼吸作用旺盛，果實內殘存的蘋果酸較少，冬季則因溫度低，呼吸作用緩慢，因此果實內蘋果酸殘存量較高，或為台灣冬季葡萄酸度偏高的生理原因。In Taiwan, winter grape has high sugar content, sweet aroma and fewer disease problems. As a whole, it is superior in quality to the summer crops. In additon, the low temperature in winter makes the grape more suitable for wine-making than its summer counterpart. In recent years, suggestions have been made to switch the main production and brewing periods from summer to winter, however, the high acidity of the winter grape, which still eludes our apprehension even after 10 years of extensive investigations, has been a obstacle which repeatedly delayed its mass production. The objective of this study was to investigate the changes in acidity, as well as the basic problems concering acid formation and degradation in both summer and winter grape with a view to pinpoint the cause of high acidity in winter crops. The summer and winter grapes followed a very similar pattern of rise and fall of its trataric acid and malic acid contents. However, the summer grape differed from its winter relative in that its malic acid level underwent a sharp drop during later stages; toward the end of maturation the acid was almost complete disappeared by way of degradation. On the other hand, the malic acid concentration in the winter grape was only partially lowered in the similar process and remained fairly high by comparison. With Golden Muscant and Blck queen, a comparison between the malic acid degradation in grape fruit and the after Veraison temperatures has shown a marked inverse correlation between the malic acid consumption and low temperatures. The acid was consumed by the fruit mainly through respiration rate, therefore the level of malic acid in the fruit would be low. On the contrary, the low temperature in winter led to reduce rate in respiration thus relatively less malic acid consumption, which invariably resulting in the high acidity of winter grape in Taiwan