The Brewer’s Window: What Temperature Should I Mash at?

“What temperature should I mash at?” is a question that all all-grain brewers will eventually ponder.  Like most brewing questions, there is no one right answer.  If you search the web and brewing texts you will find recipes with widely different mash temps called out.  If you search for “the brewer’s window” or try to find specifics on alpha and beta amylase you will see a diverse opinion on what temperature are ideal for each.

Most brewers are aware that the magic in the mash that converts starches in the malt to sugar is due primarily to two enzymes: Alpha and Beta Amylase.  Beta amylase is an enzyme that brakes straight starches (without branches) into maltose, and is the predominate factor in the fermentability of a wort.  The ideal temperature for beta amylase activity is lower than that of alpha amylase.  So in general, the cooler you mash at the more fermentable your wort will be, and the dryer (less sweet) the resulting beer will be.

Alpha amylase breaks down starches with branches, and allows the beta-amylase to further convert them to maltose.  Alpha amylase is most active at higher temperatures.   It also causes the resulting sugars produced to be less fermentable (more dextrins) and thus adds to the body of wort.

Over the past few decades it has become clear that both of these enzymes can be activated at one mash temperature range.  This is because the vast majority of malt in production today is well modified.  This it is possible to have both enzymes active simultaneously in 95% of mashes.  This method is called single infusion mashing.  This eliminates the need for various temperature steps and rests.  The most frequently sited well balanced mashing temperature is 153 degrees F.  This strikes a good balance between good fermentability and good body.

While this is good information for most beers one might brew, the question becomes when should I deviate from this mash temperature, and how far should I drift from it?  I will attempt to address these questions here.

Flexibility in mash temperature is one of the great benefits from all-grain brewing, because it allows the brewer the ability to change the character of the sugars in the wort.  There are certainly occasions when a beer style (or personal preference of a brewer) may call for highly fermentable wort.  One such example would be when brewing a style like German Altbier.  This is a style which has very high fermentability (80+ % attenuation).  While selecting a high attenuative yeast could help in this, this level of fermentability could not be achieved without lowering the mash temperature.  This would result in a cleaner, lighter tasting beer.  Conversely, there are certainly times when a sweeter, fuller bodied beer is desired.  One example could be Scotch ales, where a more malty and full body profile is desired. This is achieved by mashing at higher temperatures.

Ok, but how far should I deviate from 153F?  This is a good question and one that there isn’t total agreement on.  This question is essentially asking, what is the window that is acceptable to mash in?  This is called “The Brewer’s Window”.  I have spent a good deal of time researching this and trying to get the best, most reliable sources for what this window is and what the ranges are for both enzymes.  The Brewer’s Window is between 147-158F.

I noticed that there really isn’t a good chart that shows all this information visually (at least not that I could find).  So I endeavored to create one.  As far as I know this is the first chart that shows all this information in one place.  It is as accurate as possible.  I made an effort of reconciling contradictory information and taking the most cited and best information whenever possible.  Notice that there is also a plot showing the percent of fermentable sugars vs. dextrins at each temperature.

I hope this will be helpful to brewers.  I know it is certainly useful for me in formulating mashes.  Happy mashing!