When the mash is completed and you have finished the sparging process, you should have a kettle full of wort. Now you are ready to begin the boil!

Boils are typically 60-90 minutes. There are several benefits to the boil:

• Boiling your wort for at least 30 minutes sterilises the wort of any bacteria or other pathogens that would contaminate the finished beer thus providing a clean platform for your selected yeast strain to work.
• Boiling also volatilises unwanted chemical compounds such as the precursors for dimethyl sulfide (commonly referred to as "DMS'), which occurs naturally in traditional malt varieties, but can lead to an off-flavour in beer that is often described as "cooked corn". 
• Boiling your wort also allows proteins to coagulate and drop out of suspension, creating a clearer beer and reducing the proteins that are responsible for "chill haze".
• The boil is when bittering hops are added to the wort. Alpha acids within the hops isomerize at high temperatures, which leads to bitterness in the final beer. The reason for the process is to balance the sweetness of the malt and alcohol in the finished beer with the bitterness of the isomerized alpha acids. Isomerize alpha acids are also a good preservative which helps to keep the finished beer fresher for longer.
• Boiling also concentrates the wort. during the sparge the wort is diluted with the sparge water to ensure as much of the sugars are extracted from the grains as possible. by boiling the excess water is boiled off increasing the concentration of the sugars.