The Late Extract Addition process is very simple: the bulk of the fermentable sugars (generally malt extract) are added near the end of the boil, rather than at the beginning. Add 15-25% of your malt and/or fermentable sugars at the beginning of the boil. This will create a wort that has malt sugars and enzymes necessary for the boiling process, but creates a thinner wort for the majority of the boiling time. Add the remaining 75-85% of the malt extract during the last 15 minutes of the boil – enough time for the malt to be fully dissolved and sterilized by the boil.
There are several reasons to use the late extract brewing method. Several benefits come from reducing over-caramelization. One of these benefits is that the beer will turn out lighter, which can be difficult to do otherwise with extract beers. It can also reduce scorched malt flavors that can result from brewing high-gravity beers, or boiling the wort in a small brewpot, where the wort is more concentrated and susceptible to scorching. Another result out of the late extract method is increased hop utilization. Using the late extract method, you will get a more bitter beer than you would if you were added 100% of the malt at the beginning of the boil. This can be either good or bad, depending on the recipe. The upside is that you get better efficiency in terms of bitterness extraction from your hops. The possible drawback is that you may create a beer that is more bitter than you'd like. Many brewers choose to use about 20% less bittering hops to compensate for the increased hop utilization associated with late extract addition.
Give it a try on your next light beer and see if you like the results!