[denny]

Another reason for a longer mash is when you use a low mash temp.  Conversion takes longer at lower temps.

[bonjour]

Kai has an experiment posted on his site:  http://braukaiser.com/wiki/index.php/Mash_Time_Dependency_of_Wort_Fermentability
Although the fermentability improved, he felt that is wasn't all that much. His experiment was done at 158F.

I have tried shorter mashes with pale ale malt and it required at least a 40 min mash for complete conversion. Lighter-colored base malts may convert more quickly.

From his data it looks like there's a max of 4% increase in fermentability when mashed for 2hrs.
That's not a significant increase AFAIAC.

...but if you have the time and need that additional bump, why not go for it. 

I need that bump for my big beers,  I need all the bumps that I can get.  But on "normal" brews I agree, not significant and the difference can be easily adjusted with mash temp changes.

[SiameseMoose]

At one of the NHC's a few years ago (Chicago, 2003), there was a presentation on this topic from one of the brothers at Two Brothers. He did his PhD dissertation on this, and presented data supporting the 15 minute mash. He also stated that they did the majority of their beers this way in their brewery. When I got home I tried a comparison, making two batches of an APA on the same day, as similar as I could, with 15 and 60 minute mash times. The conventional 60 minute mash produced a much better beer. As Dave has already stated, there was a big difference in fermentability. The 60 minute mash finished at 1.012, while the 15 minute mash finished at 1.021. Both had an OG of 1.058. Granted this was a one-off home experiment, and I never tried to do it again, but I found the results compelling. It's nice to read others have had the same experience.

[4swan]

One thing that's often overlooked when commercial brewers talk about shorter mash times is their lautering time.  It can take an hour or more to sparge and lauter a commercial batch and all that time you're still at mash temp.  So, what would seem to be a 20-30 min. mash actually might go for 90 min. or more.

For the last couple of years, I've mashed for about a half hour and fly sparge and lauter for about 45 minutes.  Since I don't mash out, just sparge with 170 water,  I assume the wort is still converting in the brew kettle. So I guess my mahing time would be 75 minutes.  And I've never had problems with a high FG.

[gisbrewmaster]

I was just listening to the September 16, 2010 - Thermal Mass and Slaking Heat from Basic Brewing Radio and Chris Colby from BYO magazine discuss mash and temp in detail.  http://www.basicbrewing.com/index.php?page=radio

[dmtaylor]

SiameseMoose, thanks for sharing your experience.  While I've never actually done a one-after-the-other experiment with the same recipe for two different mash times as you did, I did make 6 small batches of different beers with differing yeasts mashing in a range from 20 to 35 minutes, and in half (3) of those cases, the attenuation suffered significantly.  Surprisingly, the attenuation also did not seem to suffer in the other half (the other 3) of cases.  I chalk this up to variability in runoff and sparge times, not to mention ingredients, which for me were not constants.  But once I started mashing for 40 minutes, all attenuability problems magically disappeared.  I have not had one single problem since.  I imagine this minimum mash time number is different for different systems, so brewers beware -- your mileage may (and probably will) vary at least a little bit.

[Pawtucket Patriot]

Here's something else to think about:

When pro brewers say "we only mash for 15 minutes," they are probably not figuring in their recirculation time, which can be significant (30-40 minutes).  During recirculation, the wort is still at mash temp and conversion is still taking place.  After all is said and done, their conversion rest isn't much less, if at all, than 60 minutes.  This is something I discovered while touring Surly Brewery in Minnesota.

[Mikey]

I think I heard that somewhere.

[hopfenundmalz]

If you have a "hot" base malt with a high degree Lintner rating, you could probably do a quick mash and by the time you got it to mash out temps it would be done.  Don't try this with a base malt with a really low diastatic power (degree Lintner) like Munich, as I had one that was all Munich that was more like 2 hours to fully convert last year.  YMMV.

[Mikey]

This is an interesting topic, but I find plenty of productive things to do during the mash time.

[Tim McManus]

Is this total mash time?  I never look at the total mash time but pay more attention to the temperature ranges I'm at for the styles and final body of the beer I'm brewing.  We don't use a "one size fits all" mash.

We'll spend 10 minutes at 121°F for a decent dough-in with a very low water/grain ratio.  Just enough to get everything wet.  Then we'll infuse up to 131°F for under-modified malts/wheat/rye for 20 minutes.  From there we decoct up to 154°F for 45 minutes.  However, we might change the mash and cut out the 131°F protein rest and go to 148°F and hold there for 30 minutes and raise up to 158°F for 15 minutes.  Again, depends on the style and how we want the body to come out.  Then we decoct to 165°F and mash out with 175°F water very slowly.  Sparging takes at least 30 minutes.

So our total mash time is over an hour, but rather than focus on that we're more focused on the temperature ranges, the amount of time we spend there, and what goodies we're extracting from the grains.

[hopfenundmalz]

This topic somes down to "What malt are you mashing".  I have a copy of the 1999 special edition on Lagers (doing some reseach on lagers), and Greg Noonan had an article titled "Secrets of the Double Decoction".  In that he states that some malts like dark munich should have a decoction, and fully modified British malts should not be subjected to lower rest temperatures, just a single infusion.

One can select the mash profile for the malt.  Use the right tool (profile) for the job. 

[mabrungard]

The duration of mashing is highly dependent on the mashing temperature as pointed out previously in this thread.  Figure 9.7 in Malting and Brewing Science shows that at a 150F mash temperature, the degree of extract peaks out at about 60 minutes of mashing time and flat-lines from that time onward.  That figure also shows that a 15 minute mash at 150F provides 90 percent of the extract potential.  

The figure also compares the extract performance at 120F.  Since this is below the starch gelatinization temperature, its not surprising that the extract potential is lower than for the 150F mash and the time to get that extract is also much longer.  

Figures 9.9 and 9.10 from that text also illustrate the time and temperature dependence of mashing.  My interpretation of the figures does support the contention that at typical 150F + mashing temperatures used with modern well-modified malts, a short mash is OK and extending the mash time doesn't really get us anything more.  I was there for the 2 Brothers mashing presentation at the NHC and heard that contention that short mashs were OK.  I did not know that it was the subject of a PhD dissertation, but I am even more inclined to believe that short mashes can work now.  

Another extrapolation of this time/temperature trend suggests that those of us performing a 160F + mash out are even less likely to need long mash time.  I'm thinking that my future mashes will be much shorter.  

[beersk]

SiameseMoose, thanks for sharing your experience.  While I've never actually done a one-after-the-other experiment with the same recipe for two different mash times as you did, I did make 6 small batches of different beers with differing yeasts mashing in a range from 20 to 35 minutes, and in half (3) of those cases, the attenuation suffered significantly.  Surprisingly, the attenuation also did not seem to suffer in the other half (the other 3) of cases.  I chalk this up to variability in runoff and sparge times, not to mention ingredients, which for me were not constants.  But once I started mashing for 40 minutes, all attenuability problems magically disappeared.  I have not had one single problem since.  I imagine this minimum mash time number is different for different systems, so brewers beware -- your mileage may (and probably will) vary at least a little bit.

Thank you for not typing "YMMV", man that annoys me

I usually mash for 60 minutes and I always seem to get crazy attenuation no matter what my mash temp was.  I've had 80+% attenuation with a mash temp of 156F, of course that could be because I used US-05, but still.  Maybe I'll try mashing for 45 minutes on my next batch for kicks. 

There's some great information in this thread.

[gordonstrong]

I haven't seen it mentioned, but the crush plays a role in mash times.  Coarser needs longer and vice versa.  The malt also needs to be properly hydrated (dry malt won't convert).  The diastatic power of the grain is a factor; if you are doing a Munich-heavy batch, or using a lot of adjuncts so that the effective DP of the mash is low, then it will take longer.  Different enzymes work at different rates, so the mash temperatures used to achieve the target wort composition will also play a role.

If you grind your grain to a flour and use high DP malt, then it will likely convert in a handful of minutes.

Personally, I don't find conversion speed the variable upon which to optimize my brewing process.

If you think you're mashing too long, do a starch test and find out.