Carbohydrates are essential in foods as an energy source (starch is the main source of human calories), a flavouring (simple sugars are usually sweet) and as a functional ingredient (sucrose allows ice cream to be soft in the freezer; xanthan gum thickens a low-fat salad dressing). Carbohydrates are a type of macronutrient found in many foods and beverages. Most carbohydrates are naturally occurring in plant-based foods, such as grains. Food manufacturers also add carbohydrates to processed foods in the form of starch or added sugar. As with all our approaches to food ingredients/constituents we will first examine the structure of carbohydrates and then try to elucidate how their structures allow them to function as they do. As their name suggests, carbohydrates basically made up from sugar and water, i.e. Cx(H2O)y, although this ratio is often not strictly true and occasionally other atoms may be present. The carbons are arranges in a chain (most often 5-6 atoms) functionalized with alcohol groups. The terminal carbon either carries either an aldehyde or a ketone functional group.