Sugar crystals are formed from sugar syrup by evaporating the syrup under vacuum to supersaturation, adding fine seed crystals, which causes the sugar "mother liquor" to yield a solid precipitate of crystalline sugar. This process is often serial.
The Process of Sugar Crystallization
The transformation of sugar syrup into solid sugar crystals is a key step in sugar production. Based on industrial processes, this involves carefully controlled evaporation and seeding.
Step 1: Evaporation and Supersaturation
Initially, syrup from evaporators is directed into specialized vessels known as vacuum pans. Inside these pans, the syrup undergoes further evaporation. This crucial step is performed under vacuum. Evaporating under vacuum allows the water to boil away at lower temperatures, which helps protect the sugar from degrading.
The goal of this evaporation is to concentrate the sugar solution until it reaches a state of supersaturation. This means the syrup contains more dissolved sugar than it normally could under standard conditions. This unstable state is essential for crystallization to occur.
Step 2: Seeding and Crystal Growth
Once the syrup is supersaturated, the crystallization process is initiated by adding fine seed crystals. These tiny crystals act as nucleation sites – surfaces upon which the excess dissolved sugar can begin to solidify and deposit.
As sugar molecules attach to these seed crystals, the crystals start to grow larger. The remaining concentrated syrup, now referred to as the "mother liquor", gradually yields solid crystalline sugar. According to the provided reference, this process can result in a solid precipitate of about 50 percent by weight crystalline sugar.
Step 3: Serial Crystallization
The reference indicates that crystallization is a serial process. This means the process might be repeated in stages to extract as much crystalline sugar as possible from the syrup and mother liquor. After one batch of crystals is formed and separated, the remaining mother liquor, still containing sugar, might be processed further to yield additional crystals.
In summary, the formation of sugar crystals from syrup in this process relies on concentrating the syrup to supersaturation through vacuum evaporation and then introducing seed crystals to facilitate the growth of solid sugar from the mother liquor.
