Like all techniques in brewing I suggest critically evaluating what is
being done to brew beer. In the case of wort boiling the goal for
all-grain brewers is to kill bacteria from malt, denature enzymes,
precipitate proteins, adjust wort gravity, remove unwanted volatiles
(such as DMS) and isomerize hop acids. The latter goal is actually
hindered by high wort gravity.
Brewers who have small brew pots and
are unable to boil the entire wort volume sometimes add dry and/or
liquid malt extracts late in the boil. These partial-mash brewers boil
the wort extracted from malt to do all the things that is required for
wort boiling, then at the end of the boil add the remaining extract in
liquid or dry form per their recipe. A short hold at high temperatures
is sufficient to kill any bacteria these ingredients may carry since
liquid and dry malt extracts have already been heat-treated during
manufacture and do not have high bacterial loads. After the
high-gravity wort has been cooled the gravity is adjusted with water.
The benefit to this method is that wort produced from grain is boiled
at a normal gravity along with hops just like an all-grain, full wort
volume brew and all of the requirements of boiling are met. Dry and
liquid extracts do not need to be boiled because these ingredients were
boiled when concentrated at the extract plant. Furthermore, boiling
extracts has absolutely no affect on efficiency. So the simple answer
is that this is a sound method and has no obscure pit-falls that may
end up causing disappointment.
Your next question is about keeping your beer warm during conditioning.
This is a real world problem for commercial breweries selling
bottle-conditioned beers. As you point out, storing beer in the
basement or an underground cellar reduces the air temperature to the
average earth temperature of the location of the cellar. In most parts
of the world the average earth temperature is about 55 ºF (13 ºC). This
impairs the speed of bottle conditioning, and for many ale strains is
really too cold to get much carbonation at all.
This is why bottle-conditioned beers are typically stored in warm
cellars controlled to a comfortable temperature of about 75 ºF (22 ºC).
This is plenty warm for the yeasties to do their work in a reasonable
time frame and is not so warm that the beer starts to prematurely age
because of high storage temperature. This practice is relatively common
in Europe and the United States among brewers who bottle-condition
their beers. Duvel in Belgium, Sierra Nevada in California and New
Belgium in Colorado are three breweries I know who have warm cellars. I
know that at Sierra Nevada beer is held for about a week before being
released for sale.
So in the commercial world of brewing where time is money, warm
conditioning reduces the number of cases that are sitting around
waiting for carbonation to happen. Bean counters like to minimize this
type of inventory and warm conditioning helps control inventory and the
conditioning process. At home the economic drivers of inventory control
are different, but why wait 2 weeks to sample your next tasty brew when
you can cut down the time to 1 week? There is no reason whatsoever not
to practice this method . . . I declare open season on