Author: Marshall Schott

The primary purpose of each xBmt is to determine whether certain variables impact a beer such that blind participants are capable of reliably distinguishing a difference. To this end, we utilize the triangle test, a sensory analysis tool whereby blind participants are served 3 samples of beer, 2 from one batch and 1 from the other, then asked to select the one that is different. Because participants are unaware of the nature of the xBmt and asked to perform the same task, the triangle test is perfect for the type of “citizen science” we regularly perform; however, it is designed only to measure the perceptions of participants, whether they’re capable of distinguishing a difference, it cannot tell us whether there is actually a difference. Accomplishing such a task would require certain lab equipment and knowledge, neither of which I possess.

But I recently met someone who does.

A few days after I shared the results of the Pils malt boil length xBmt, I was contacted by a dude named Daniel Hillesheim who said he had the equipment and know-how to “quantify the concentration of DMS” in the 2 xBmt beers. Exciting! We’d already determined tasters were incapable of reliably distinguishing a Pils malt based beer boiled for 90 minutes from one boiled for only 30 minutes, but that left me wondering if the level of DMS in the short boiled beer may simply have been below the threshold of perception, or if there really wasn’t any present in either sample. After a brief back-and-forth, I sent samples from each batch to Daniel’s lab in Tennessee, packaging them in different sanitized yeast vials to avoid biasing him.

What follows is an explanation of Daniel’s process and the results he found, the details of which may be difficult for some to understand, but we wanted to ensure the methodology was made available for scrutiny. A simpler summary can be found at the end of this article for folks like me who get headaches trying to make sense of this stuff. Get your thinking caps on and prepare for a trip down chemistry lane, shit’s about to get deep.

| METHOD |

A 1µL sample was injected into an Agilent 7890 gas chromatograph (GC) equipped with a 30 m DB-Wax column and flame ionization detector (FID). Injector port temperature, oven ramp profile, and detector temperature were picked to optimize separation of the key analyte, dimethyl sulfide (DMS). Initial conditions were based on a Restek guide called Analyzing Alcoholic Beverages by Gas Chromatography. The injector temperature was set to 200°C, the detector temperature was set to 250°C, the oven profile began at 40°C for 1 minute, ramped to 150°C at 4°C/min, then finally ramped to 220°C at 10°C/min. The carrier gas is He at 45 cm/s column velocity. A split injection method was employed at a ratio of 5:1. Reagent grade DMS and ethanol (EtOH) were purchased from Sigma Aldrich. HPLC grade water was purchased from Fisher Scientific.

| RESULTS |

A standard consisting of 5µL of DMS in 5mL of HPLC grade water was prepared and injected to determine the retention time of DMS (1.72 minutes). Similarly a standard of EtOH was prepared and the retention time identified as 3.63 minutes. Data collection on the beer samples followed. Figure 1 shows a selected section of the graphs of the beer samples and the DMS sample in overlay. The large peak at ~4 minutes is EtOH. No detectable DMS was present in the beers.

To confirm that no matrix effects were responsible for shifting the DMS signal in the beer, 10µL of the DMS standard mixture was added to 5mL of the 90 minute boil sample, and that mixture was injected. Figure 2 clearly shows the appearance of a new peak with the same retention time as the DMS standard not present in the unadulterated 90 minute boil sample confirming that the peaks near DMS are other compounds.

| CONCLUSION |

Two beers of the same recipe consisting of 93% German Pils malt were produced simultaneously utilizing the exact same process with a single exception– one was boiled for 30 minutes while the other was boiled for 90 minutes. The impetus for this xBmt was to test the conventional wisdom regarding increased risk of dimethyl sulfide (DMS) in beers produced using a large portion of lower kilned Pils malt and the oft recommended longer boil for such worts. Results of the triangle test failed to achieve significance, indicating a general inability for participants to reliably distinguish between the different beers. However, as is common with most xBmt findings, the question of whether there was an actual difference in levels of DMS remained. A sample from each batch was sent to a lab for objective analysis, the results of which validated the results of the original xBmt: neither the 30 minute boil nor 90 minute boil samples contained measurable levels of DMS.

As was previously discussed, it’s possible the lack of DMS in these beers is a function of the high modification of the Pils malt used (Best Malz) and that less modified malts, such as those that are floor malted, might produce higher levels of DMS. But, it’s just as possible our understanding of the relationship between DMS and boil length is simply lacking, that our access to modern technology, higher quality ingredients, and better knowledge about brewing processes has reduced the likelihood of problems brewers of yore had to worry about. It’s these types of ideas I hope provoke the modern homebrewer to humbly question convention and embrace the thrill of treading new ground.

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