Malt extract is created by mashing grains in the same way an all-grain brewer might and sparging to produce wort. However, that wort then needs to be concentrated down to a thick syrup by boiling off most of the water. Most maltsters boil the wort under vacuum pressure to lower the boiling point of the water, but the heat, time, and reduced water activity tend to darken melanoidins in the wort, which are the primary coloring agents. This darkening of the melanoidins takes place through what is called a Maillard reaction and is triggered by heat and low water content.
Further, if a can of malt extract is stored at a higher temperature or left on the shelf for an extended period of time, these same melanoidins darken even more, which is a good reason to use fresh, refrigerated malt extract if at all possible.
The net result is that even malt extract made with very light-colored Pilsner malt will be darker than comparable all-grain wort from the same malt. This makes it difficult to brew very light colored beers such as Kölsch with malt extract.
A secondary issue is the fact that many extract brewers use a concentrated boil—typically, only 3–4 gal (12–16 l) for a 5 gal (19 l) batch. This concentrated boil leads to kettle caramelization thanks to the aforementioned Maillard reaction, as well as the risk that some extract may settle to the bottom and scorch the pot. The net result can be a further darkening of the wort, depending on how concentrated the boil is and how much scorching takes place.
As Dave Carpenter explains in “The Virtues of Being Late,”, because you really only need to boil wort long enough to sanitize the extract and isomerize the alpha acids from your hops, you can reduce the potential for kettle caramelization by reserving some of a recipe’s extract for late in the boil (usually the final 10 to 15 minutes). Doing so can help preserve the best color you can in your extract beer.
PHOTO: MATT GRAVES