Pros and Cons of Decoction Mashing

1. Enhances production of flavor and aroma compounds.
2. Reduces mash pH for better conversion and easier runoff.
3. Less trub in main boil and at chilling.
4. Less chance of raw starch carryover to kettle.
5. Extracts, coagulates and precipitates tannins, proteins and silicates.
6. Allows thicker mash for earlier rests.
7. Better gelatinization of starch.
8. Breaks down protein matrix thus releasing more starch and improving extraction.
9. It's the traditional way to make some beers.

Cons:

1. Complicated.
2. Requires more equipment.
3. Takes a lot more time.
4. Darkens beer.
5. Extracts tannins as grains are boiled.
6. Danger of scorching.
7. Uses more energy.
8. Must be careful about starch released in final decoction.
9. "The classical three-mash system is a long-drawn-out affair and the chief criticism which has been leveled against it is that mashing is too intensive (i.e., protein is degraded too far)." Jean deClerk

Note that tannin extraction has been listed as a pro and a con. The good news is that some of it is complexed and dropped in the decoction and that as the tannins have been largely extracted in the decoctions one need not be so careful about sparge temperature and pH. The bad news is that the tannins have been released and long lagering is usually required for them to drop out.

Suggestion for obtaining the thinnest part of the mash for lauter decoction: Use a large kitchen sieve as a stuykmanden, i.e., push it down into the mash and ladle out the liquid.