2. When we boil sugar and water together, the concentration of sugar water will get higher and higher with the continuous evaporation of water. When the concentration reaches a certain level, the result will be precipitated after cooling, which is actually the method of making rock candy.
3. If we want the syrup to keep a certain concentration without crystallization after cooling, we need to add acidic substances such as citric acid or tartar essence in the process of boiling syrup, or we can use lemon juice to replace these acidic substances.
4. During boiling, acidic substances will decompose sugar into monosaccharides which are not easy to crystallize, thus preventing the syrup from crystallizing after cooling. This process of decomposing sugar into monosaccharides is called conversion, and the converted syrup is called converted syrup.