Unlike sugarcane, which is grown in tropical or sub-tropical climates, sugar beets are grown in temperate regions of North America, Europe and Asia. Beet crops can be stored for several months before being delivered to beet sugar factories. Processing involves several important stages, including:
Cleaning and Juice Extraction – Sugar beets are washed to remove dirt before being fed into a slicing machine. Here the beets are cut into small pieces to maximize the surface area for juice extraction.A multi-cell countercurrent diffuser uses water to extract the sugar from the beets. The diffuser is operated at a temperature above 75 degrees Celsius to minimize microbial growth. This process extracts roughly 98 percent of the sugar in the beets in the form of raw juice.
Purification – During purification, the raw juice goes through a process called carbonatation, a series of steps using milk of lime and carbon dioxide, which react to facilitate the precipitation of impurities. Between stages, the juice is often filtered.After carbonatation, sulfur dioxide is injected to lower the pH and remove color. Regulation of pH above 7 is essential to prevent formation of invert sugar. At high alkalinity, total decomposition of sucrose, glucose and fructose occurs.
Evaporation and Crystallization – After being purified, the juice passes through multi-effect evaporators where it is concentrated to form a thick juice consisting of 60-65 percent dissolved sugar. The thick juice is mixed with lower grades of liquid sugar to constitute mother liquor.The mother liquor is further concentrated by being boiled in vacuum pans and then seeded with fine sugar crystals to induce further crystallization. The product proceeds to a basket centrifuge to remove the crystals.
Drying – The final step in the process involves the drying of the product in either rotary or fluidized-bed driers. Before storing or packing, the white sugar must be cooled to below 45 degrees Celsius to prevent hardening or development of color.