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Pickling using salt or sugar has been a commonly used method for preserving food since time immemorial. Sugar plays a dual role here. It lends a sweet taste and also helps release the flavors of the preserved food, be it fruit, vegetable, or any other. It holds good when making umeshu also.
The role of sugar in umeshu
The main principle behind using sugar for making umeshu is the need for a favorable osmotic pressure. Osmotic pressure maintains the concentration between two liquids and prevents the absorption of the sugar in the water. Instead, the presence of the sugar and the resultant osmotic pressure brings about the process of osmosis which causes a release of flavors and absorption into the liquid. As a consequence, water moves from the side of a lower sugar concentration – the ume plums to the side of a higher concentration – the water-alcohol-sugar mixture.
The cells of the plums, like all other fruits and vegetables, have a permeable membrane surrounding them called the cell membrane that regulates the movements of molecules into and out of the cell. To make water move out of the cell membrane, we need to put the plums into a concentrated sugar solution, as we do while making umeshu. As more and more water comes out of the plums, the cell membrane structure breaks down, losing its semi-permeability. Once this happens, the seasoning liquid – a mixture of sugar, water, and alcohol soaks into the plums. It preserves the plums while infusing the juices and flavor of the plums into the umeshu.
Which sugar works best for umeshu?
Rock sugar or rock candy is the most preferred sugar for making umeshu owing to its property of being slow-melting. Rock sugar dissolves gradually over time unlike refined white sugar or brown sugar that dissolves instantly. When the rock sugar slowly dissolves, it also slowly builds the osmotic pressure, causing a slow release of juices and flavors from the plums. When the juices are released and the plums dehydrated, the seasoning liquid becomes a delicious fruity umeshu.
Why is white sugar not preferred to make umeshu?
White sugar or granulated sugar dissolves instantly in the water and alcohol mixture. Due to this, the osmotic pressure and concentration of the liquid reach a high right from the very beginning of the umeshu-making process itself. As a result, the flavor of the ume plums does not release as smoothly as it would with rock candy, and the texture of the plums is also adversely affected. To get delicious fruity umeshu, the concentration of the seasoning liquid must build gradually. White sugar would shock the plum cells and hamper the flavor release.
In this way, sugar is essential for making delicious umeshu.
