Maize (Zea mays L. ssp. mays, pronounced /'me?z/; also known in some countries as corn), is a herbaceous plant domesticated in Mesoamerica and subsequently spread throughout the American continents. After European contact with the Americas in the late 15th and early 16th centuries, maize spread to the rest of the world. Maize is the most widely grown crop in the Americas (332 million metric tons annually in the United States alone). Hybrid maize, because of its high grain yield as a result of heterosis ('hybrid vigor'), is preferred by farmers over conventional varieties. While some maize varieties grow up to 7 metres (23 ft) tall, most commercially grown maize has been bred for a standardized height of 2.5 metres (8 ft). Sweet corn is usually shorter than field-corn varieties. Dextrins are a group of low-molecular-weight carbohydrates produced by the hydrolysis of starch. Dextrins are mixtures of linear a-(1,4)-linked D-glucose polymers starting with an a-(1,6) bond. Digestion of starch starts in mouth by the salivary alpha amylase to maltose gives intermediate products as dextrins which, according their colour with iodine, can be called erythrodextrin (dextrin that colours red) and achrodextrin (giving no colour). During malting and mashing process of the grain also dextrins are produced during the fermentation of starch. Dextrins are also formed on the surface of bread during the baking process and contribute to the flavour and colour and crispness. Industrial production is roasting starch powder under more or less acidic conditions causing hydrolysis and rebranching of the starch molecule. These type of dextrins are also called pyrodextrins. White and yellow dextrins are partially or fully water-soluble low viscous powders that are optically active. Under analysis, dextrins can be detected with iodine solution, giving a red coloration. Starch roasted with little or no acid is called british gum.