What Gives Each Beer its Unique Characteristics?

The huge variety of beer styles available is a result of the near-infinite possible combinations of different types of malted barley with alternative grains, hops and other flavoured ingredients. For example, using barley that has been roasted for longer and at a higher temperature will give beer a darker colour and toastier flavours. Different varieties of hops will change the bitter characteristics and aromas of the finished product. And even the type of yeast used can develop flavours in different and exciting ways.