[Lazy Ant Brewing]

In the book farmhouse Ales, Phil Markowski cites a 1905 publication by R.E. Evans that some Northern French breweries commonly boiled simple pale ale worts for nine to 12 hours.

Other than reducing volume and boosting gravity, what  does this accomplish?

In recipes from modern breweries, I notice 90 minute boils with some frequency as compared to the more usual 60 minutes.

Comments please, and thanks in advance.

[morticaixavier]

I know some breweries had underpowered boilers that took a really long time to get to a boil and sometimes never really did. instead they would hold the highest temp they could manage for a very long time.

That said, there are historical records from british breweries boiling for 3-5 hours for strong beers. You will certainly develop some color and some flavor as you boil down that hard.

[kramerog]

This is pure speculation but longer boils might be necessary for some modern breweries to drive off DMS due to the closed configuration of their boil kettles.

[Jimmy K]

This is pure speculation but longer boils might be necessary for some modern breweries to drive off DMS due to the closed configuration of their boil kettles.

Modern kettles have a condensate trap that keeps vapors from dripping back into the kettle.

[reverseapachemaster]

Traditional thought in many parts of Europe was that the longer the boil the better the beer and if you had inefficient equipment you might only get a simmer rather than a full boil and the option to boil longer might have been alluring for that reason. The section of Farmhouse Ales you reference explains that these beers were boiled longer to develop sweetness.

Those traditional processes and ideas about brewing remained popular, particularly in rural areas, well past the industrial revolution and probably would have survived in even greater usage had the two world wars not ravaged so much of Europe and made brewing difficult due to confiscation of brewing equipment and the shortage of grain. However, even today there are still rural parts of Europe where traditional brewing techniques persist and modern equipment like thermometers and hydrometers are absent from the brewhouse.