Golden syrup is an amber-colored syrup made from sugar with a much richer texture and deeper aroma than simple syrup. It also contains acid, which helps make the mooncake pastry tender. Alkaline water -- also known as kansui, or jian sui in Chinese -- is an alkaline solution made from sodium carbonate and potassium carbonate. It is often used in Asian pastries and ramen noodles. It acts a bit like baking soda, keeping dough fluffy and moist without introducing too much gas. It also adds a yellow color to dough (like making egg noodles without egg). In mooncakes, alkaline water neutralizes the acid in the golden syrup, so the dough doesn't taste sour.