Glycæmic Index is influenced by:

The degree of processing/cooking/chewing: the more processed/refined a food is, the higher the Glycæmic Index. Foods which are more textured, chewy, crunchy, fibrous tend to take longer to be digested and release their glucose into the blood stream more slowly than soft, refined or pre-cooked foods. Long grain white rice has a lower Glycæmic Index than quick cooking brown rice and multigrain bread has a lower Glycæmic Index than wholemeal bread. Food that has not been properly chewed also has a lower Glycæmic Index - it may also give you indigestion. The method of baking bread appears to influence its Glycæmic Index; traditional slow rising bread dough (e.g. sour dough fermentation) can have a lower Glycæmic Index than breads made with rapid-rise dough.