Originally Published by Jim Busch in Brewing Techniques (Volume 4, Number 5)
Munich malts are unique in their production in the malthouse, their chemical profile, and their application in the brewery. This article summarizes Munich malt’s production methods, chemical constituents, and color and flavor attributes and explains how brewers can exploit them to create classic beers of distinction.
The Road to Munich Begins in the Malthouse
To understand Munich malt and how it differs from ordinary pils or domestic six-row malts, we must first understand how it is made. Like all European malts, Munich malts are made by steeping two-row barley in warm water and nurturing it through a warm germination phase; the steeping is what begins the germination of the seed.
Some large modern malthouses germinate grain in large drums or in a tower system in which grain is steeped at the top before being dropped into germinating chambers below. Other malthouses use the Saladin box, a long rectangular device with a track for the malt turning machine, which “walks” up an internal lane, turning and aerating the grain. In classic floor makings, the wet seed is spread out to form a bed about 3–6 in. deep to allow the seed to sprout. Over a period of three to six days, the seed develops a rootlet and a sprout. Many brewers prefer malt made from floor malting and Saladin boxes because it tends to produce plumper and more uniformly sized kernels.
The chemical changes that take place during this phase are complex and involved, generally fixing the malt’s protein modification and enzyme spectrum. Beta glucans present in the cell walls are almost completely degraded, and roughly half of the total barley protein is hydrolyzed. This protein modification liberates free amino nitrogen (FAN) and amino acids, which are beneficial to many brewing reactions.
At the conclusion of the germination phase, the rootlets and sprouts are removed and sold as a secondary product for feed. The product that remains for brewing is referred to as green malt. All malt begins as green malt.
Green malt is kilned under carefully controlled temperature and time requirements to yield a particular malt that has specific color and chemical composition. Different styles such as pils, caramel, black patent, or Munich malt are made by varying the temperature and duration of the kilning or by allowing the malt to be steeped warm before final drying to bring out the sugars. Roasted malts, such as chocolate and black patent, undergo the same germination and kilning processes as do base malts, but are then placed in a special roasting drum. Pils malt is characteristically light-colored and high in enzymes. To make pils malt, green malt is kilned at 185 °F (85 °C) to yield a malt of between 1 and 3 °SRM (Lovibond).
Munich malts, on the other hand, are meant to be much darker, typically around 7 °SRM; they are also available in even darker versions of between 10 and 20 °SRM. To achieve these colors, the green malt is “stewed” under progressively higher air temperatures, which promotes a degree of saccharification of the malt before it is finally kilned at 212 °F (100 °C). The longer the malt is held at 212 °F, the darker the Munich malt will be.
In the beginning of the kilning process, green malt has considerable moisture content, typically in the 45–50% range. Early in the kilning, this water content is reduced to 5–10% moisture over a period of roughly 24–48 hours. In Munich malting, the moist air is recirculated in the kiln, helping to accelerate the production of amino acids and reducing sugars that will subsequently form coloring compounds through Maillard reactions. As the moisture content is reduced, the maltster increases the temperature until it reaches 212 °F, and it is held at this temperature for as long as 5 hours.
The combination of a long drying phase at a low temperature and a high kiln-off temperature is essential to creating Munich malts. At lower temperatures, the malt dries and forms abundant amino acids and reducing sugars. At higher temperatures, the Maillard reactions are favored. The chemical changes that occur during this stewing/kilning process — including the production of melanoidins — are essential to the nutty/malty/bready/toffee characteristics that Munich malt imparts to beer.
Brewers talk a lot about melanoidins in beer, their creation through malting and kettle reactions, their negative effects when oxidized through poor wort handling techniques (hot-side aeration), and their positive effects when left in the reduced state (1). In Munich malt, melanoidins are the result of specific manipulations of malting conditions, as described in the previous section. To understand the exact source of the malt’s unique flavor characteristics, we need to look further and examine the chemistry at work within the malting process.
Melanoidins are one product of a general reaction (Maillard reactions) between a reducing sugar and amino acids. Sometimes these reactions are also called nonenzymatic browning reactions.
In Maillard reactions, reducing sugars and amino acids react when heated during the kilning step, producing an Amadori compound of the form 1-amino-1-deoxy-2-ketose (diketosamine). From the Amadori compound (which may occur in many forms), melanoidins can be produced through any of several pathways. One path involves dehydration reactions (1-2 enolization), producing furfurals, while another (2–3 enolization) produces reductones. Reductones can then react with oxygen, sulfur, or nitrogen to produce certain classes of compounds (oxygen heterocyclics, sulfur heterocyclics, and nitrogen heterocyclics, respectively). Furans, an oxygen heterocyclic, impart toffee/caramel flavors. Pyrroles and pyrazines, which are nitrogen heterocyclics, are responsible for nutty flavors (2,3). Pyrazines can also impart harsh, burnt, and sometimes acrid characteristics, but they are much more prevalent in darker roasted malts, chocolate malt, black malt, and roasted barley than in Munich malts (3). Sulfur heterocyclics impart bready, cracker, or biscuit flavors. Some have unpleasant characteristics such as stale bread or old beer flavors.
A related chemical reaction to melanoidin formation is called Strecker degradation. Like the classic Maillard reactions, Strecker degradation involves an amino acid such as leucine or valine reacting with a reducing sugar to form an aldehyde and a Strecker aldehyde, mainly during the malting process. Strecker aldehydes such as isovaleraldehyde tend to impart flavors described as biscuity or malty (3). These aldehydes can remain unchanged and be carried over into the finished beer or react with additional reducing sugars to produce melanoidins.
The predominant flavor compounds present in Munich malts are furans, pyrroles, and Strecker aldehydes. Although the chemistry and names may seem complicated, the compounds created are essential to imparting what many brewers describe as classic malty and bready aromas and flavors to beer.
The key point here is that some experimentation is a good idea in selecting Munich malts. While a certain degree of confidence can be placed on buying good European floor-malted malts, there can be no substitute for the practical results in a given brewhouse and recipes. I have had great success with DeWolf-Cosyns, Durst, and Weyermann Munich malts and general displeasure with some of the domestic Munich malts that I have tried.
It should be noted that the Maillard reaction and its principal products — melanoidins and flavoring compounds — have been studied extensively. Most of the interest in this chemistry relates directly to the food products industry. The same reactions that impart such a distinctive character to our favorite beers are also responsible for many of the flavors found in foods such as coffee, chocolate, popcorn, and cooked meat.
Munich Malt in the Brewhouse
The reactions that produce the flavors and aromas desired in intensely malty beers are mostly the work of the maltster. The fact that the vast majority of the melanoidins in a malty beer can be extracted through mashing with Munich malt is a blessing for brewers. All the brewer needs to do is determine the correct proportion of the malt to use in a given recipe to yield the desired effects.
Recipe formulation: Although each brewer will make judgments based on his or her own tastes, I find that 5–10% Munich malt contributes plenty of character to most ales. Lagers, on the other hand, may require much larger percentages, especially if the intent is to brew characterful Bavarian Dunkels or Bocks. Several authors have proposed using Munich malt as the majority of the grist for Bocks and particularly Doppelbocks (4). This approach, combined with decoction mashing, results in very distinctive and full-flavored lagers.
Mashing procedures: The one area that you should be concerned with is careful mashing procedures that minimize oxygen pickup. Although this warning is generally true for all mashing, it is particularly important when working with Munich malts. Melanoidins in their reduced (unoxidized) state provide excellent flavor stability by serving as antioxidants. Oxidized melanoidins, however, are blamed for some particularly unpleasant flavors and rapid deterioration in packaged beer. This is especially significant to craft brewers who bottle their beer and ship it over great distances.
Enzyme activity: Despite the fact that Munich malt is kilned off at around 212 °F, the long, gradual process that leads up to this temperature is the key to Munich malt’s enzymatic profile. A typical pils malt may have a diastatic power (rating of enzyme activity — the higher the number the more the enzymes) of 105 degrees Lintner (dL); Munich malt is usually around 50 dL. This diastatic power rating may seem small relative to pils malt, but it is plenty to convert the starch present in the malt. It may be insufficient to convert a significant amount of starch from adjuncts, but a typical beer made with Munich malts would not normally use a high quantity of adjuncts but would instead use standard malts of high enzymatic power.
Aromatic malt: Aromatic malt is a specialty malt from Belgium that is in many ways similar to Munich malts, but in other ways it is closer to caramel malt. Like Munich malt, aromatic malt undergoes the same low-temperature kilning procedure of drying and liberating amino acids and reducing sugars. The difference arises in the kiln-off temperature; in aromatic malt production, the final kiln-off is at 239 °F (115 °C), resulting in a darker malt of 20–25 °SRM; the diastatic power, however, drops to 30 dL. Aromatic malts are useful in some recipes, but with its lower enzyme content and much higher coloring potential it is best kept to proportions below 20% of the grist.
A Unique Malt for Distinctive Beers
Munich malt is a powerful tool that brewers can use to produce classic malty continental lagers and robust ales. High-quality Munich malts, in particular those produced in classic European floor makings, are sure to add a distinctive malty/nutty/biscuity contribution to the finished beer.
Maltsters achieve high melanoidin levels in Munich malt through careful control of kilning times and temperatures. Brewers use this malt as a source of these highly beneficial flavoring compounds not only for their contribution to flavor and aroma but also for longer term stability of the packaged product. The fact that Munich malts retain a moderate degree of diastatic enzyme activity allows brewers to use this malt at any percentage they desire.
If you haven’t brewed with Munich malts lately, I suggest you start now!
I’d like to thank Steve Alexander, Pierre Jelenc, and Dan McConnell for their assistance with the chemistry involved in Maillard reactions.
(1) George Fix, “The Detriments of Hot Side Aeration,” zymurgy 15 (4), pp. 34–40 (Winter 1992).
(2) Manfred Moll, Ed., Beers and Coolers (English edition by Intercept, Ltd., Andover, Hampshire, England, 1994), p. 140.
(3) Timothy O’Rourke, “Making the Most of Your Malt,” The New Brewer 11 (2), pp. 20–21 (March/April 1994).
(4) Darryl Richman, Bock (Brewers Publications, Boulder, Colorado, 1994).
(5) Henry B. Heath, The Source Book of Flavors (AVI Publishing Co., Westport, Connecticut, 1981), p. 114.
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