The freezing point of pure water is 0°C. Any other substances dissolved in the water will lower the freezing point; where inorganic salts are present it may be considerably lower. If a weak solution is frozen, at first pure ice will be separated, thereby increasing the concentration of dissolved substance in the residual solution making its freezing point lower still. The effect of such freezing concentration on the product is different from case to case and has to be taken into account when selecting the most appropriate freezing technique.