RIMS versus Decoction


The Great Texas Mash-Off

by Louis Bonham and Andy Thomas (Brewing Techniques - Vol. 6, No.1)

Two brewers put their favorite mashing techniques to the test in a friendly showdown between new-fangled technology and Old World tradition.

Decoction mashing — the traditional continental technique of separately boiling portions of the mash — enjoys a near-mythic reputation in the minds of many amateur brewers. Whether because of the complex and daunting nature of the process, its traditional place in the brewing of some of the world’s most difficult (and delicious) styles, or the indoctrination of a generation of home brewers as to its inherent superiority for lager brewing,* decoction mashing is commonly regarded as the signature style of the perfectionist small-scale brewer.

Decoction advocates argue that the technique produces a rich maltiness, color, and complexity that infusion mashing simply cannot duplicate and that it provides better yields from undermodified continental malts. That this method can yield spectacular results is beyond dispute; some of the world’s greatest and most famous lagers — including Augustiner Edelstoff, Steinet Dunkel, and Pilsner Urquell — have been and continue to be brewed using decoction mashing techniques.

Nevertheless, not everyone agrees that decoction mashing is essential to making great lagers, or even that it offers any real advantage to today’s brewers. Skeptics point to the fact that decoction mashing was developed to cope with the problems of severely undermodified malt and a lack of accurate temperature measurement and control — problems modern brewers no longer face. Detractors also argue that the application of modern brewing techniques can produce all of the claimed advantages of decoction mashing in a much more efficient brew cycle (1).

Indeed, in the same way that many indisputably great beers are produced by decoction mashing, many superlative lagers are produced using infusion mashes. Even many German breweries have quietly switched from decoction to infusion mashing.

The debate over whether decoction mashing is superior to other techniques is moot for many new microbrewers because it is usually too expensive and time consuming to implement on a commercial scale.* But for amateur brewers, who do not face commercial constraints, this question remains a hot issue.

Does decoction mashing hold inherent, qualitative advantages for small-scale brewers? We decided to try to find out.

*The apparent sources of the decoction mythos for home brewers are Greg Noonan’s excellent books, Brewing Lager Beer and New Brewing Lager Beer (2,3). While Noonan’s claims regarding the inherent superiority of decoction mashing (see page 133 of New Brewing Lager Beer, for example) have been widely quoted, he cites no authority for this thesis, and indeed there appears to be little empirical data supporting it.

*Exceptions can be found, however. Perennial GABF medalist Stoudt Brewing Company (Adamstown, Pennsylvania), for example, uses an unusual decoction technique in which only the specialty malts are boiled. Saxer Brewing Company (Lake Oswego, Oregon) has also taken several medals for its decoction-brewed beers (see the article by Alan Moen in the December issue of BrewingTeclmiques). The Acadian Brewing Company (New Orleans, Louisiana) uses traditional Bavarian decoction techniques for many of its beers, including a superb Helles Bock produced using a triple-decoction mash. Franconia Brewing Company (Mt. Pocono, Pennsylvania) is currently test brewing German-style lagers using traditional decoction methods.

Dueling Brews

To answer this question, I, Louis Bonham, posed the following challenge to my fellow Foam Ranger (and unapologetic decoction advocate) Andy Thomas: Choose any style and recipe that best showcases the advantages of decoction mashing, and let it compete against the same beer brewed using a more modern technique. We would brew our batches simultaneously, using identical ingredients, but with one difference — Andy would use a triple-decoction mash, and I would use a step-infusion technique on a state-of-the-art recirculating infusion mash system (RIMS) (see Dion Hollenbeck’s article on page 56 for an overview of RIMS brewing). The beers would then be fermented and aged under identical conditions and then blind-tasted by a panel of experts.

Andy readily agreed to the challenge. He selected a Munich Helles recipe that called for wort with an original gravity of 1.055 (13.5 °P) made from 100% German Pilsener malt, hopped to approximately 23 IBUs. This recipe approaches the upper end of the gravity range and the lower end of the bitterness range for the style, making it ideal for accentuating any differences in malt character from the brewing systems.

What follows is a detailed account of our experiment. As you will see, the results were surprising and in many respects counterintuitive. We therefore decided to repeat the experiment using a darker beer (traditional Bock) and a “neutral” recipe designed by BJCP Master Judge Scott Birdwell. (See the recipe box on page 47.) We also decided to include a control beer using a single-infusion mash in our second experiment. This portion of the experiment was handled by current Foam Rangers Grand Wazoo Steve Moore.


As stated earlier, each of us began with identical grain bills, drawn from the same bags and crushed on the same mill, and identical reverse osmosis–filtered water treated to approximate the Munich profile (see the box, “Munich Water Treatment,” page 48). We chose our own grist-to-water ratios and mash schedules.

The purpose of the experiment was to test the quality of the finished beers, not to compare extract efficiencies, so we decided to use a “no sparge” technique (see box, “The ‘No Sparge’ Formulation,” on page 48). This method is inefficient, but we felt it would be particularly appropriate here because it removed the sparge variable from the experiment and also allowed us to pinpoint an exact original gravity.

Both the Helles (experiment 1) and the Bock (experiment 2) recipes were designed to allow for the production of more than the target number of gallon-points to the kettle (in other words, the sweet wort was a fairly high gravity of 1.074–1.083 S.G. [18–20 °P]). After mash-out, we each drained our sweet worts to the kettles and diluted them to the target preboil gravity. Any sweet wort in excess of the target preboil volume was discarded before the boil.

The sweet worts were then boiled in converted Sankey keg kettles for the same amount of time (70 minutes), hopped identically, and then cooled with the same two-stage counterflow wort chiller. We determined that we would further dilute the finished worts to the target original gravity, then transfer 6 gallons of each to 7-gallon carboys. The worts were then aerated, inoculated with 2 quarts each of the same yeast starter, and fermented in the same refrigerator. After fermentation, 5 gallons of each beer were transferred to Cornelius kegs, lagered, and then force-carbonated at the same pressure and temperature.

The Variables

RIMS: The RIMS mashes were done on a modified prototype of the BrewMagic system currently marketed by SABCO Industries (Toledo, Ohio). I opted to use a water-to-grist ratio of 1.25 quarts/lb and a version of the “50-60-70” mashing schedule recommended by George Fix for under-modified or less well modified malt (see references 1 or 4 or Fix’s An Analysis of Brewing Techniques in “Further Reading”). The grain was mashed in at 122 °F (50 °C), held for 30 minutes at this temperature, boosted to 140 °F (60 °C) and held for 30 minutes, brought up to 158 °F (70 °C) and held for 30 minutes, and finally boosted to 168 °F (74 °C) for mash-out. All temperature boosts were performed by a baffled gas burner under the mash tun (I used a natural gas jet burner in the first experiment, but because Andy obtained a harder kettle boil from propane I switched to propane to eliminate this variable in the second experiment). The in-line electric RIMS heater was used only to maintain the various temperature rests.

As is typical of many other well-designed and implemented RIMS systems, the mashing process was almost effortless — all I had to do was heat the water to the appropriate strike temperature, pump the foundation water into the mash tun and RIMS heater, pour the grain in, pump in the remaining mash water, set the temperature controller, turn the pump on to begin the recirculation, and adjust the flow rate valve. Apart from resetting the controller for the various steps and lighting the gas burner for the temperature boosts, the mash required no other user intervention.

Decoction: The decoctions were performed according to the schedule shown in the box, “Mash Schedules,” on page 50. A triple-decoction schedule is typical of mashing methods used by many Bavarian breweries, though rest mash temperatures vary for different styles. Decoction volumes were about 33%, 33%, and 40% of the mash. The rest mash temperatures allowed for a protein rest at 122 °F (50 °C) for about an hour, a saccharification rest at 149 °F (65 °C) for a little over an hour, and mash-out at 167 °F (75 °C). The first and second decoctions were allowed to saccharify at 159 °F (71 °C) for about 20–30 minutes (until they passed the iodine test) before boiling.

This decoction schedule is not Old World traditional and cannot be compared with the rigorous Weihenstephan schedule. Schedules such as Weihenstephan’s grew out of the ancient need to cope with undermodified malt and to control brewing temperatures in the absence of modern instruments. Rather, the decoction schedule used in these experiments is a variation of that used in modern Bavaria and takes advantage of the more highly modified nature of modern malts by eliminating protein tests in each decoction cycle. Further, Andy typically shortened his decoction boil time so that he might finish the decoctions in a reasonable amount of time. Longer boil times certainly increase yields; however, yields were not an issue in this experiment, and Andy has found that shorter boil times are sufficient to extract traditional Bavarian-style flavors.*

The decoctions were performed using a 6.6-gallon Centurion stainless steel restaurant pot (318 stainless steel with a stainless-clad ¼-in. aluminum wafer on the base) and a standard propane Cajun cooker. The decoctions were returned to an uninsulated stainless keg for resting. (It is generally considered appropriate to return the decoctions to a standard 48-quart cooler, but the stainless keg arrangement has shown little heat loss when the air temperature is above 80 °F [27 °C] and calm.) The decoctions were ladled to and from the rest mash using a ½-galIon stainless steel kitchen pot with minimum splashing of aerating. After mash-out, the mash was lautered in a 48-quart cooler using a slotted copper tubing as a manifold.

*Greg Noonan notes in a private communication with BrewingTechniques that his experiments with shorter boil times confirm that though longer boil times do increase flavor, the difference is generally not noticeable enough to warrant the extra time.

Single infusion: Steve brewed the single-infusion control beer using a cylindrical Gott cooler with a Phil’s Phalse Bottom (Listermann Manufacturing Company, Inc.; Cincinnati, Ohio) as the mash/lauter tun. Mash-in was conducted with 1 qt/lb of water at 170 °F (77 °C), yielding a mash temperature of 155 °F (68 °C). After a 90-minute rest, the mash was recirculated manually until the wort ran clear and then drained to the kettle. Because it appeared that this mash generated less than the target number of gallon-points (the 1 qt/lb mash thickness yielded an insufficient amount of liquid), Steve was permitted to batch-sparge with 2 gallons of 170 °F (77 °C) water, which rinsed a sufficient number of points to the kettle.

Fermentation and Lagering

Both the Helles and Bock recipes called for the Bavarian-style Wyeast Laboratories (Hood River, Oregon) #2206 yeast. In each case, a very fresh Wyeast package was used to inoculate 3 cups of 1.020 S.G. (5 °P) starter, which was then used to inoculate 6 quarts of aerated 1.036 S.G. (9 °P) starter. After cooling to approximately 50 °F (10 °C), each batch was aerated with an aquarium pump stainless steel aeration stone setup (0.22-micron filter). After inoculating each batch with 2 quarts of starter, the worts were placed in a refrigerator set at 50 °F.

Munich Helles: In the case of the Munich Helles (experiment 1), the worts (original gravity 1.055 S.G. [13.5 °P]) were actively fermenting within 12 hours, and the ambient temperature was then allowed to rise to 56 °F (13 °C). Seven days after pitching, the kräusen had fallen and the gravity of both batches was 1.013 S.G. (3.25 °P); the temperature was then gradually lowered to 38 °F (3 °C). The gravity leveled out within 30 days after pitching and five gallons of each batch were transferred to Cornelius kegs. The kegs were then lagered for another two weeks at 33 °F (1 °C) and force-carbonated to a calculated 2.5 atmospheres.

Bock: The Bock experiment proved much more problematic. The worts (original gravity 1.067 S.G. [16.5 °P]) were pitched with a fresh starter in the manner described above and similarly showed active fermentation within 12 hours, at which time the temperature was allowed to rise to 56 °F (13 °C). Because the kräusens rose and fell identically, and in a fashion very similar to that of the first experiment, it was assumed that all was well and no gravity measurements were taken.

After 10 days, the temperature was allowed to rise to 60 °F (16 °C) for 24 hours for a brief diacetyl rest and then was slowly lowered to 38 °F (3 °C). Six weeks after pitching, 5 gallons of each beer were transferred to Cornelius kegs, where gravity readings were taken. At that point, we discovered that despite the outward appearance of a normal fermentation, the beers had in fact stuck: the RIMS and infusion-mashed beers were at 1.030–1.032 S.G. (7.5–8 °P), and the decoction-mashed beer was a whopping 1.039 S.G. (9.75 °P).

Samples were then force-tested* and examined microscopically. These tests confirmed the absence of infection, but although significant amounts of viable yeast cells were present in all three batches they simply would not ferment any further. We have not been able to come up with a definitive reason for the problem fermentations, though the #2206 strain is known for being a bit temperamental. According to the manufacturer, the yeast can have problems fermenting high-gravity worts such as Bocks if they are underaerated or not oxygenated with pure oxygen (though this can be typical of lager yeasts) (5).

*Force testing is a simple method for checking up on your sanitization techniques at various stages of the fermentation. 1 had removed 100 mL from each batch (postaeration, prepitching) to sterilized baby food jars covered with foil. According to my usual practice, I incubated the jars at 80 °F (27 °C). The rule of thumb is that if unpitched wort goes two to three days without any changes or signs of growth, your sanitization is OK; less than 24 hours, and you’ve got big problems. More than three days means you’re muy macho (Andy’s was still clear after five days). In this case, I repeated the tests after encountering the stuck fermentation.

Stuck fermentation remedied. Because of the marked differences in gravity (and therefore alcohol content), we ruled out treating the worts by oxygenating them for fear that it would oxidize more alcohol in the RIMS and infusion beers and thus skew the results of the experiment. We therefore decided to handle the matter more conservatively by growing up a fresh batch of yeast, allowing the beers’ temperatures to rise to 56 °F (13 °C), and then repitching.

By the time the new yeast was grown up (eight weeks after the original yeast was pitched), the RIMS and infusion beers were down to 1.022 S.G. (5.5 °P) and the decoction beer was at 1.037 S.G. (9.25 °P). One-quarter of the cultured yeast slurry was added to each of the RIMS and infusion mashes, and half was added to the decoction mash. Repitching caused the RIMS and infusion batches to reach a terminal gravity of 1.019 S.G. (4.75 °P) fairly quickly. The decoction mash, however, stubbornly refused to kick off and instead continued to inch its way down slowly. (Attempts to find an explanation of this rather bizarre yeast behavior have been fruitless.) After more than three months, the decoction beer finally reached a terminal gravity of 1.022 S.G. (5.5 °P), and we decided that this was close enough. All three beers were then lagered and force-carbonated to a calculated 2.5 atmospheres.

The Taste Tests

Samples from the two experiments were tasted “blind” by a panel of judges aware of the nature of the experiment but not the identity of the beers. The judges were asked to evaluate the beers comparatively for appearance, aroma, head retention, mouthfeel, malt character, hop character, and defects, as well to give their general comments and an approximate BJCP score on a range of 1–50, 50 being best. See the table “Evaluation Summary” on page 52 for the results at a glance.

Experiment 1 — Munich Helles: Samples of the first experiment were evaluated by Tim Case (Brewmaster, The Houston Brewery) and by the Best of Show panel at the 13th Dixie Cup homebrew competition in Houston, Texas: Scott Birdwell (BJCP Master Judge), Carl Saxer (BJCP National Judge), Chuck Cox (BJCP Master Judge), Dean Doba (BJCP Certified Judge), and a professional brewer who prefers to remain anonymous. The panelists made the following observations:

·         Appearance: Four of the six judges found the RIMS beer to be slightly darker or more golden; two discerned no real difference.

·         Aroma: The panel reached no clear consensus on aroma. Two judges found slightly more DMS in the RIMS beer, while one seemed to find more in the decoction beer. This same judge found the noble hop aroma to be more noticeable in the RIMS beer, but another found the RIMS beer’s hop aroma fruity and the decoction beer to have a hint of vegetable. Still another found the RIMS beer to have a grainier aroma.

·         Head retention: Three of the six judges found the head retention to be about the same. Two found the decoction beer to have slightly better retention. One thought the RIMS beer laced better.

·         Mouthfeel: Three of the judges found the RIMS beer to be slightly heavier or fuller, two found them equivalent, and one found the decoction beer to be slightly chewier.

·         Malt character: Three judges found the RIMS beer to be maltier and sweeter, while one found just the opposite. The other two judges detected more of a grainy flavor in the RIMS than in the decoction.

·         Hop character: The only apparent consensus was that the hop character was subdued, which was not surprising given the design of the recipe. Three judges found that the hops came out better in the RIMS beer, while one critiqued the RIMS hoppiness as sharp and fruity. Another felt that the maltiness of the RIMS beer overwhelmed the hops.

·         Defects: Three of the judges found no detectable defects in either beer. One judge found a hint of phenols up front in the RIMS beer, which he hypothesized might be the result of hot-side aeration. Another found the RIMS beer to be more “ale-like,” while another found the decoction beer to be a bit thin and the RIMS beer to have a slight grainy aftertaste.

·         Bottom line: Five of the six judges preferred the decoction mashed beer; one preferred the RIMS beer. Of the judges who assessed numeric scores, most scored both beers in the high 30s to low 40s on a BJCP 50-point evaluation, and one judge scored them both considerably lower.

·         Three months later. … This initial evaluation took place when the beers were about six weeks old and thus still very young for a Munich Helles. Three months later, after the beers had had a chance to lager further, they were sampled blind at a Foam Rangers meeting. While both beers had improved with age, the basic findings were unchanged: the RIMS beer was considered to be slightly maltier, but overall the decoction-mashed beer was considered better.

Experiment 2 — Bock: Samples from the second experiment (which included the single-infusion control beer) were first evaluated by Steve Daniel (BJCP Master Judge), Scott Birdwell (BJCP Master Judge), Jim Parker (AHA Director), Steve Roberts (Brewmaster, Boondoggles Brewery, Clear Lake, Texas), and Fred Eckhardt (BJCP National Judge and author of The Essentials of Beer Style and other works). At this point the beers were 15 weeks old. The panelists made the following observations:

·         Appearance: The panelists had no clear consensus on which beer was darker. Two panelists found no discernable differences between the three. Two panelists thought the decoction beer was darker and richer; one thought the opposite was true. (Analysis with a spectrophotometer revealed that the beers were all within 3 °L of each other; the RIMS beer was the darkest, followed by the decoction-mashed beer.)

·         Aroma: Again, the panels reached no clear consensus, though they did tend to prefer the RIMS and decoction-mashed beers over the infusion-mashed beer. Two panelists opined that the decoction-mashed beer had a maltier aroma, while two others found more DMS in the decoction-mashed beer’s aroma.

·         Head retention: Three panelists indicated that the decoction-mashed beer had nominally better head retention, while the other two found no differences.

·         Mouthfeel: Three judges reported that the decoction-mashed beer had the most mouthfeel, followed by the RIMS beer. One judge found the RIMS beer richest, followed by the decoction-mashed beer. One judge found that the infusion beer seemed fuller, but thought that the fullness might be due to an astringent note he detected.

·         Malt character: All five panelists found the RIMS beer to have the best malt character followed by the decoction-mashed beer. Two panelists detected some astringency in both the infusion and decoction-mashed beers.

·         Hop character: Three panelists found the decoction-mashed beer to have the most hop character. One found that the infusion beer had the most apparent bitterness, and another found the RIMS beer to be the best balanced.

·         Defects: The judges routinely indicated that the beers were too young and would improve with age. All five found that the infusion beer was slightly astringent or metallic. One found the decoction-mashed beer to have an inordinate amount of DMS in the aroma. Another found the decoction-mashed beer to be too sweet.

·         Bottom line: Four of the five panelists preferred the RIMS beer; one preferred the decoction-mashed beer. Two of the judges preferred the infusion beer over the decoction-mashed one, and none preferred the infusion beer to the RIMS beer. The scores for the RIMS beer ranged from 35 to 42, with an average of 37.8. The decoction beer’s scores ranged from 30 to 40, with an average of 34.4, and the infusion beer scored from 30 to 38, with an average of 33.2.

Two days later… Two days later, the beers were re-evaluated by an impromptu panel comprising George Fix, Dave Miller, and John Maier (Brewmaster, Rogue Ales; Newport, Oregon). By this time, however, the RIMS beer had noticeably “gone off,” and what had been pleasant caramel notes in the flavor were replaced by sherrylike tones — a clear sign of oxidation. The cause is not immediately clear, but rough handling of the kegs, exposure to temperature extremes, and air introduced during the late stages of fermentation may have contributed to the problem. It is also possible that the RIMS beer suffered a bit of hot side aeration, making it more susceptible to premature staling (though if that were the case the beer probably would have had phenolic, metallic, or cardboard flavors rather than a sherrylike note).

This panel’s findings were as follows:

·         Appearance: Two panelists could discern no differences between the beers; one felt the decoction-mashed beer might be a shade darker than the others.

·         Aroma: Two of the panelists found the RIMS beer to have slight objectionable notes in the aroma. One felt the RIMS beer had the maltiest aroma.

·         Head retention, mouthfeel, and hop character: No discernable differences noted.

·         Malt character: One panelist felt that the decoction-mashed beer had very good maltiness, while the sherry notes in the RIMS beer interfered with his ability to taste anything else. A second panelist also preferred the smooth maltiness of the decoction-mashed beer, but noted that the RIMS beer had an intense, complex maltiness with lots of Munich and caramel. The third panelist noted that the RIMS beer had a “caramelly sweet” profile that was richer than the other two.

·         Bottom line: All three panelists preferred the decoction-mashed beer and rated the RIMS and infusion beers as roughly equivalent. One panelist rated the decoction-mashed beer at 36, the infusion beer at 32, and the RIMS beer at 30, although he was quick to point out that the oxidized state of the RIMS beer made it impossible for him to meaningfully evaluate it. A second panelist rated the decoction-mashed beer at 40 and the infusion and RIMS beers at 38. The third panelist did not provide numerical ratings.

The Final Analysis

The contrasting nature of the comments in the tastings may be attributable to the fact that the judges were aware of the premise of the experiments and were reaching to find differences between the beers, which were actually very similar in many respects. The specialty grains in the Bock recipe as well as the “no-sparge” technique probably contributed significantly to the beer’s flavor, regardless of the mash technique used. The very similarity of the beers appears to confirm that mash methods other than decoction can produce fine beers.

Technically, however, the tasting panels preferred the decoction-mashed Helles overall to the RIMS version, though they did find the RIMS Helles to be maltier and darker in color. On the other hand, the second experiment’s judges preferred the RIMS Bock over the decoction-mashed version, though the high final gravity of the decoction Bock undoubtedly skewed the results. These judges preferred both the RIMS and decoction-mashed versions over the single-infusion mashed control beer, though it fared well too. Again, the RIMS beer was darker and judged to be maltier than the others.

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