Sunday, May 3, 2009

why boil the malt extract?

While figuring out the boil gravity and hop utilization during yesterday's light ale brewing I began wondering why malt extract needs to be part of the boil at all. Certainly it's important to pasteurize it, so it needs to be added to the kettle at some point, but what purpose is served by including it in a full hour-long boil? Increased boil gravity reduces hop utilization, so that alone seems like a good reason to keep the extract out as long as possible.

I did a little searching and found a couple of articles:
Both of these support the idea that the extract can be added very late in the boil. They also perpetuate what I understand to be misinformation about caramelization (as opposed to Maillard reactions; see McGee or Palmer), but the basic point that the sugars will be altered through the application of heat, and that may or may not be what you want, is sound. That occurs when extract or excess sugars settle to the bottom of the kettle.

Cited advantages of adding the extract at the end are better hop utilization, lighter color, and avoidance of off flavors.

According to the first article, sugars and enzymes aid in the extraction of the alpha acids from the hops, so some quantity of extract in the boil would be desirable. The author recommends 15% - 25%; this suggests that the wort alone after steeping specialty grains might also be sufficient. The second article seems to support that idea.

Why is this an extract-specific phenomenon? I suppose it would be that the sugars in an all-grain wort are more completely dissolved and do not accumulate at the bottom of the kettle. That seems intuitively sensible.

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