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Two approaches to mash management
Modernists argue that nowadays maltsters already do much of the work in preparing the grain that brewers in earlier times could only do in the mash tun. They also point out that even with multi-step infusion, brewers can initiate all the important enzymatic conversions without mash boiling.
In contrast, there is a group of brewers who take a middle road, saying that some beer styles - usually from the German brewing culture - can benefit from decoction under certain circumstances, whereas other styles - usually from the British and Belgian brewing cultures - are already designed for infusion only.
The decoction Maibock was perceived as more intense on the nose, with less sweetness but more alcohol (Photo: Weyermann®)The German brewhouse tradition
Simplified, the traditional German brewhouse method is based on a multi-stage extraction process in which the wort is extracted from thin mashes that are moved back and forth between different vessels - in the past by ladeling, today by slurry pumping. This process achieves the best results with a liquor-to-grist ratio (by weight) of about 3:1 to even 5:1. The mash-in liquor for such a low-viscosity mash can be up to 80 per cent of the brew kettle volume.
A portion of the mash (about one-third) is then repeatedly transferred to a special cooker where it is slowly heated to the boiling point. The boiling time of each partial mash amounts to 15 and up to 60 minutes (for darker beers), after which the boiled part is returned to the main mash to cause a gradual temperature rise there.
Empirical values and measured values
Even today, some brewers use a sophisticated and time-consuming double or triple decoction scheme to achieve the mash-out temperature. In the distant past, decoction brewers judged from their experience how much mash to draw off and boil at each stage and how many times to repeat the decoction to bring the main mash up from the mash-in to the optimal mash-out temperature.
However, with the invention of the thermometer, and subsequent advances in biochemistry along with an increased understanding of grain enzymes, it was suddenly no longer necessary for brewers to rely on the known temperatures of well water and boiled mashes, and on easily measured decoction volumes. With these two great achievements in mash control - temperature measurement and understanding of enzymes - brewers who still insist on the pre-industrial decoction method need to make better arguments than just its "necessity".
The Infusion Maibock was convincing on the palate as well as with its balance on the finish. (Photo: Weyermann®)The British brewhouse tradition
In British-style brewhouses, mash is never boiled. This makes the classic British brewing method much simpler than the German one. British mashing invariably uses a high-viscosity, stationary grain bed with a liquor-to-grist ratio of perhaps only 2:1, or sometimes even lower, usually in a dual-function mash-lauter tun. This means that the ratio of mash-in liquor to the net kettle volume in the British thick mash brewhouse process is almost the reverse of that in the German thin mash brewhouse process.
British brewers often keep the mash at only one temperature in the diastase range. After saccharification and a short recirculation of the wort, lautering into the brew kettle runs relatively slowly. It can take up to 90 minutes or longer. During this process, the mash is simultaneously and continuously sparged with hot brewing liquor. Often, the mash temperature is reached through and not before sparging. The depth of the liquid above the mash is usually kept constant at around 3 - 5 cm.
Both test brews were brewed according to identical specifications.Arguments pro decoction
Although the old arguments for decoction based on the simplicity of volume measurement to control of the mash temperature no longer apply today, its protagonists nevertheless extol some advantages:
Decoction is more effective in breaking down starch grains and cell walls, which leads to higher extract efficiencies; decoction produces more intense malt aromas through non-enzymatic browning as a result of the Maillard reaction; it is practically oxygen-free. Proteins can be better precipitated by decoction, resulting in a clearer wort with less trub.
Arguments pro infusion
Many arguments for infusion are based on the things that decoction does not do or require:
The infusion process is faster and saves energy. With modern highly modified malts, very good efficiencies can also be achieved with the infusion process. The initial investment in a decoction-capable brewhouse is much higher, and modern malt specialities such as melanoidin and caramel malts, for example, offer the same aromas that are expected from decoction.
A common high-short procedure was chosen for the infusion mash and a two-step procedure was used for the decoction mash.Two test brews
The only question that remains is whether the differences in taste justify the extra effort of decoction. For this purpose, a simple Maibock recipe was designed, which was brewed on two consecutive days - first by infusion, then by decoction - in the pilot brewery of the Weyermann® Malting Company in Bamberg with the same ingredients according to identical specifications (see table).
As a beer style, Maibock with its clean malt flavour was perfectly suited for this test.
The grain bill for both beers consisted of 88 percent Pilsner malt, seven percent Caraamber® and five percent Carafoam®. The purpose of the two specialty malts was a full body as well as a color that conformed to the style. Since this experiment was more about malt than hops, the bitterness (from the traditional Spalter Select variety) was deliberately throttled back to about 25 IBU.
The aroma was provided by the "noble" landrace Tettnanger. The yeast was also deliberately restrained with the low-ester SafLagerTM S-189. Consequently, the fermentation temperatures for both beers were kept at 12 °C, i.e., at the lower edge of the working range of this yeast, which kept the formation of fermentation by-products within limits.
The sensory truth
Both beers are basically very similar. Their minimal differences in the relevant aspects can perhaps only be perceived and put into words by tasters with sensory training. As a rough generalization, the elaborate decoction Maibock appears somewhat more alcoholic as well as less full-bodied and sweet.
Especially in the finish, it is also a little more hop-bitter. Interestingly, the color assessment was somewhat unorthodox because, contrary to theory, most tasters could not detect any color difference between the two beers. In terms of foam formation, the tasters gave the nod to the infusion Maibock, whereas there were only marginal differences in the bouquet. However, the infusion Maibock ranked clearly higher on the palate and more balanced in the finish. It also scored slightly better in the areas of body and mouthfeel, as well as malt-hop balance.
It was particularly striking that the decoction mash did not show a greater amount of melanoidin-related, bread-like, caramel-sweet, toffee-like and malty-bitter aromas, which is, after all, one of the key arguments of the protagonists of mash boiling. The explanation probably lies in the fact that the targeted use of modern specialty malts of good quality in an infusion mash can produce the same or very similar sensory results as a decoction mash.
Of course, it is up to each individual brewer to decide whether the slight differences in taste between the two brewhouse processes are worth the extra effort in terms of personnel, time and energy. However, the empirical-sensory experiment presented here allows us to conclude that the "necessity" argument for decoction is hardly compelling nowadays, even for classic German beers like Maibock.
