Another significant point that distinguishes winter tea from spring tea, and this is the most important one, is that Winter teas have a more obvious aroma than spring tea thanks to the extreme climate condition and shorter sunshine exposure.  But this benefit does not come without sacrifice, Polyphenols and amino acids, which are the two key points in creating the sweetness and the body for oolong tea, will decrease dramatically in winter.  As a result, winter tea will tend to have a stronger aroma but a slightly thinner body than spring tea.

via A Guide to Appreciating Winter Harvest Oolong Tea from Taiwan – Taiwan Sourcing.