A method for controlling sugar crystallization in a closed-loop manner, comprising: determining a size of sugar crystals in a sugar slurry, wherein the size of the sugar crystals is determined based on an initial size of the sugar crystals, a previous supersaturation degree of the sugar slurry, a change in time, and a crystal size constant; determining a consistency value of the sugar slurry, wherein the consistency value of the sugar slurry is the weight parant of solid sugar in the sugar slurry and is determined based on an initial consistency value of the sugar slurry, a previous size of the sugar crystals, the previous supersaturation degree, a level value of the sugar slurry, and a consistency constant; determining a first brix value of a mother liquor, wherein the first brix is determined based on a second brix value of the sugar slurry and on a previous consistency value; determining a purity value of the mother liquor, wherein the purity value of the mother liquor is the weight percent of sugar in the solids and is determined based on the level value of the sugar slurry, the second brix value measured from the sugar slurry, a purity value of a syrup supplied to the sugar slurry, an amount of the mother liquor, and the first brix value of the mother liquor; determining the supersaturation degree of the sugar slurry, wherein the supersaturation degree of the sugar slurry is determined based on a sugar saturation point of the sugar slurry, the first brix value of the mother liquor, and the purity of the mother liquor; and controlling a syrup feed valve position, a steam valve position, a vacuum pressure, or any combination thereof based on the supersaturation degree. determining a size of sugar crystals in a sugar slurry, wherein the size of the sugar crystals is determined based on an initial size of the sugar crystals, a previous supersaturation degree of the sugar slurry, a change in time, and a crystal size constant; determining a consistency value of the sugar slurry, wherein the consistency value of the sugar slurry is the weight parant of solid sugar in the sugar slurry and is determined based on an initial consistency value of the sugar slurry, a previous size of the sugar crystals, the previous supersaturation degree, a level value of the sugar slurry, and a consistency constant; determining a first brix value of a mother liquor, wherein the first brix is determined based on a second brix value of the sugar slurry and on a previous consistency value; determining a purity value of the mother liquor, wherein the purity value of the mother liquor is the weight percent of sugar in the solids and is determined based on the level value of the sugar slurry, the second brix value measured from the sugar slurry, a purity value of a syrup supplied to the sugar slurry, an amount of the mother liquor, and the first brix value of the mother liquor; determining the supersaturation degree of the sugar slurry, wherein the supersaturation degree of the sugar slurry is determined based on a sugar saturation point of the sugar slurry, the first brix value of the mother liquor, and the purity of the mother liquor; and controlling a syrup feed valve position, a steam valve position, a vacuum pressure, or any combination thereof based on the supersaturation degree.