Ask Mr. Wizard

The Importance of Mash Thickness


Harry Mittermaier — Baden bei Wien, Austria asks,

Thanks for your recent BYO+ video on mash thickness. According to some German brewing literature the question of mash thickness is treated differently for pale and dark beers, where a thicker mash and more sparge water are recommended for dark beers and vice versa. The underlying idea is that a thorough sparge with more water aids to extract more body and “graininess” from the grist. Is that more of a German myth?


Nice to know that our readers are also watching our video content online. Mash thickness is one of those things that many a brewer takes for granted because it simply lacks many obvious brewing implications. In the world of commercial brewing, it’s important to have a mash thin enough to mix and pump. And it’s also important to maintain some degree of thickness to help preserve enzymatic activity that can falter in thin mashes. So, why not just choose a happy middle ground for all brews and not worry?

I want to begin this discussion by referencing two texts. My favorite German brewing text is Wolfgang Kunze’s Technology Malting and Brewing. The newest book in my library, The Comprehensive Guide to Brewing (Basarava, Savel, Basar, Basarova, and Lejsek), has quickly become a stellar reference. While both references make mention of mash thickness, neither text leaves the reader with much substance to really consider. My takeaway from these texts is that mash thickness is more of an engineering concern than anything. That’s not surprising because brewing texts have a hard time covering a topic, the art of brewing, that is not universally agreed upon.

Let’s think about what happens when a very thin mash with a first gravity of about 12 °Plato (1.048 SG) is produced and its wort is run to the brew kettle with no sparging. Not exactly the paradigm for brewing efficiency, but also not unheard of in the commercial world. Kirin Ichiban, as the name suggests, is made using just the first wort runnings from the grain bed. Besides a cool name, sort of like first press, the wort used to produce beer like Kirin Ichiban is indeed different from sparged worts because the grain is only bathed in first wort liquid. For all of you BIAB (brew-in-a-bag) and no-sparge brewers reading this, feel good about your brewing choices! Only surrounding grist with first wort, that is the wort that first is made when liquor and grist meet, means that only part of the grist solids are extracted into wort.

When a mash bed is partially or totally drained of first wort and sparge water is sprayed upon the grain bed, the environment around the grain solids quickly changes. Liquid density drops, pH begins to increase, enzymes are washed away with first wort, polyphenols/tannins continue to leach into the sparge water like tea-leaf tannins in second and third steeps of tea brewing, and undissolved starches are extracted.

This is a whole lot to unpack. Suffice to say, mash thickness is more than an engineering concern. Let’s go back to the first wort example. Whether brewing something like a Pilsner, helles, golden ale, or a pale North American lager, it makes sense that thin mashes would be appealing. On the other hand, if a brewery is producing dark and bold beers known for a bit of snark, starting with a thicker mash that relies upon sparging to pull attitude from malt makes perfect sense. And what about decoctions? The thick mashes pulled into the decoction kettle are malt heavy and leave behind the relatively enzyme-rich thin mashes to quench their heat upon returning from the cooker. All these topics relate to mash thickness.

The short answer to your question is no; I personally do not believe that the relationship between mash thickness and beer flavor is a German brewing myth.

I attended a great presentation about decoction delivered by Klaus Zastrow. At the time, Klaus was the Brewmaster of the Anheuser-Busch Brewery in St. Louis, Missouri, and a brewer with lots of street credentials. I was just a 26-year-old brewer with lots of questions. During Klaus’ Q&A session, I mustered up the nerve to stand up and ask what decoction mashing contributed to beer flavor. I have always thought that a slow response is a sign of a good question and was excited when Klaus briefly fumbled and quietly mumbled something unintelligible in German. “I am not sure how to say this in English, but decoction mashing imparts a certain astringency and depth. Yes, it gives beer [gusto].”

Mash thickness, sparging, decoction mashing, and gusto are all intermingled. And there is little argument in my mind that mash thickness does indeed play an important role in shaping the flavor of beer.