Article

Removing Trub, Munich Malts Explained, D-rests, and Dip Hopping

Q After wort chilling, most of the trub is left on the bottom of the kettle. For years I’ve poured this residual trub through a stainless steel strainer with the hops acting as a filter. Should I leave all the trub out and what advantage does this have? Neither I nor my family and friends notice anything off regarding flavor and aroma.

Royce Faina
Philadelphia, Pennsylvania

Whirlpooling is one popular technique that helps separate the wort from the break material formed during boil and chilling. Photo by Charles A. Parker/Images Plus

A The range of methods used by brewers to produce beer certainly is not lacking of variety. There are commercial brewers of great, hoppy beers who accept high wort losses when high hop loads are separated from wort using whirlpools designed for more moderately hopped beers. Some brewers use centrifuges to maximize wort yield flowing from the brewhouse into fermentation and are also making terrific beers. And others use hop backs for a range of purposes including whole hop removal from wort, late hop aroma addition, and as a filter to remove trub from boiled wort. All of these wort-saving methods are great options depending on the size of the brewery and the types of beers being brewed. Suffice to say, it sounds like you are happy with your beers, the method you are using is not some sort of Frankenbrew technique, and you have your method developed around this practice. Keep on doing what you’re doing! Also keep reading for another take on this topic.

There is a common brewing adage that goes something like this: When the opportunity presents itself to remove stuff from beer, seize the sediment! Whatever falls out of wort or beer is probably not going back into solution and because gravity is always on the clock, removing solids along the journey from wort to beer just makes sense. It’s also true that some of these solids contain flavor-active compounds that can adversely affect beer flavor. A few examples of continual removal of solids includes trub removal from hot wort in a whirlpool vessel, cold wort flotation, cold wort settling, skimming brandt/braun hefe from the surface of fermenters, racking after primary fermentation is complete, and cone-blows when fermenting in a unitank. And the use of special devices, like the Sierra Nevada Hop Torpedo, confine hops and/or spices inside the contraption so that beer can be infused with flavor in a controlled fashion that also minimizes beer losses.

There is a common brewing adage that goes something like this: When the opportunity presents itself to remove stuff from beer, seize the sediment!

Another real benefit to many of these techniques is a reduction in wort/beer losses. In the language of commercial jargon, it sounds like one of the main reasons you began straining your “whirlpool bottoms” was to increase your yield. And that’s a great approach to brewing, independent of batch size. Why waste good stuff when options are on the table? Brewers have a long history of developing methods to increase efficiency. The best methods improve efficiency while simultaneously improving beer qualities, such as aroma, taste, flavor stability, improved microbiological stability, or better beer foam stability. There’s another brewing truism related to this discussion: Whenever pondering weird and funky brewing practices, be they old or new, follow the money for the likely explanation. Hope this discussion was helpful and that you continue to brew efficiently!

Q I have noticed a lot of variation in Munich malts from different maltsters and I’m trying to understand the difference between Munich Light, Medium, and Dark malts. I can order Munich Light in 5, 8, 15, and 30 °L, and Munich Dark comes in 8, 15, and 50 °L colors. There are also malts offered as Munich 10 °L, Munich 20 °L, and Munich 60 °L, which I assume are Munich Medium. What does Light, Medium, and Dark really mean?

The BYO “Tips From the Pros” (https://byo.com/article/using-munich-vienna-malts-tips-from-the-pros/) didn’t provide many answers to this question. In fact, this reference says that Munich Malt has a color rating of 5–20 °L, Which adds more confusion because I see 30, 50 and 60 °L versions.

Robert Waligora
Solon, Ohio

A The differences among specialty malts is confusing for a number of reasons, including how the same description, such as Munich or crystal, is used for a wide range of malts. And some maltsters use creative names, for example a German-sounding word or a word with an oddly placed umlaut, to suggest a malt type. Let’s start diving into your question by first digging into the typical process used to produce Munich malt.

All malt types share commonalities through the “green malt” phase of production. Green malt is the term used to describe germinated grain kernels before the kernels are dried. To produce green malt, maltsters steep barley to increase moisture content from about 8% to about 45%. Steeping not only turns on metabolic processes, it also washes the surface of the dry kernels, floats away light debris and chaff, leaches polyphenols/tannins from the grain husk that can inhibit germination, and delivers oxygen to the grain embryo. Various steeping and aeration methods are used by maltsters because steeping sets the stage for germination and no one approach works for all. Indeed, most maltsters declare steeping to be the most critical step of malting.

By the end of the 36–48 hour steeping process, the hydrated kernels have entered the “chit” stage of germination as seen by the emergence of a rootlet from the embryo end of the kernel. The chit malt is either transferred to germination or the steep tank is drained and prepared for use as a germination vessel. Equipment aside, the germinating barley is attended using a combination of periodic turning, blowing cool and moist air flow through the grain bed, and/or spraying water on the surface to the bed. These methods help maintain temperature, moisture, and oxygen uniformity within the germinating “piece,” or lot, of germinating malt. Turning also helps prevent rootlets from tangling and individual kernels from being collected into masses that make germination control difficult. Germination times vary based on the primary control parameters of moisture content and temperature, but most malt spends 3–5 days in germination. Particulars aside, green malt exits germination and is either transferred to a kiln or roasting drum.

Before moving into kilning, let’s take a brief detour into the topic of color development and Maillard browning. The cascade of chemical reactions between so-called reducing sugars and free-amino groups during cooking are collectively described as Maillard browning, or sometimes “the” Maillard reaction, and the products of these changes are known as Maillard reaction products (MRPs). Technical details of the reactions aside, higher protein grain, increased moisture content after steeping, increased malt modification, and a moderate, high-moisture step during kilning all increase the concentration of reactants that lead to MRPs. Maltsters like to use the term “levers” when referring to these process variables they can “pull” when producing malt. More on this to follow.

In general, Munich malts have more color, more flavor intensity, especially with respect to malt aroma, a higher degree of modification, and usually are less enzymatic than lighter base malts like Pilsner malt. Maltsters achieve these differences by pulling on the levers that increase MRPs, especially degree of modification and kilning profile. The ratio of soluble protein to total protein, referred to as the Kolbach Index (KI) or S/T in the malt world, is one index of modification that is also directly related to the concentration of free-amino nitrogen (FAN). As green malt FAN increases, so do MRPs. This is why Munich malts have higher S/T ratios than lighter malts produced by the same maltster. Increased malt modification also increases reducing sugar concentration, but not by much.

Kilning regimen is key to Munich malt production, and the big levers in kilning that maltsters pull are high “air-off” moisture during the early stages of drying (this is accomplished by recirculating air during kilning to increase the piece temperature without losing moisture) and a prolonged curing time at ~212–221 °F (100–105 °C) for color and flavor development. Pilsner malt, as a comparison, is gently kilned without any intentional delay in drying, curing time is shorter and curing temperature is lower to minimize color development. In general, Munich malts have more biscuit, dark bread, and nutty aromas than Pilsner and Vienna malts, the color typically ranges from about 5–20 °L (12–52 EBC or 6–12 SRM), and the enzyme content is usually high enough for 100% inclusion. The uses for Munich malts are very broad, making this general classification one of the most commonly used specialty malts in brewing.

OK, now for the discussion about color you probably have been waiting to read. To make things less confusing, ignore adjectives used to describe color because malt color is numerically defined. Descriptors like light and dark don’t provide any more information than color values and often confuse things because one maltster’s light Munich may be another’s dark Munich.

Another confusing thing is the wide range of color found beneath the Munich malt umbrella. Given that Munich malt is named after a German city, let’s take a look at Munich malts produced by three German maltsters. Weyermann has three conventional (not organic) Munich malts with colors of 6, 8, and 9 °Lovibond. Bestmalz produces two conventional Munich malts with colors of 6 and 11 °Lovibond, and Ireks produces a single conventional Munich malt at 8 °Lovibond. It looks like the German maltsters keep Munich malts within a pretty narrow color range; not a huge surprise considering the precise nature of German malting and brewing.

Traveling across the pond to North America, Munich malts with higher colors are found. Briess produces 10, 20, and 30 °Lovibond Munich malts and Gambrinus makes 10 and 30 °Lovibond Munich malts. Not sure why North American maltsters push colors up, but it probably has something to do with really pulling on the levers! Just like with beer where triple imperial IPAs were needed because the garden variety IPA was too pedestrian, dark Munich malts from Germany apparently needed more umph.

The interesting thing with these darker Munich malts is that their recommended upper grain bill limits are much less than the 100% cap on Munich malts from Germany. And that of course is because the kiln lever was pulled hard enough to denature enzymes. North American 20 and 30 °Lovibond Munich malts don’t list enzyme values with their malt certificates of analyses (COAs) because there is really nothing to report; these darker malts may be called Munich but they don’t share the enzymatic strength of their European ancestors.

Finally, there are products with Munich in the name that are not “Munich malt” as discussed earlier. Weyermann produces three malts in their Cara family of products called CaraMunich® (I,II, and III). The Swaen maltings from the Netherlands has their family of GoldenSwaen© caramel malts and produce GoldenSwaen© Light and Dark Munich malts. It’s clear by reading about these products that they are not Munich malts, nor are they marketed as such. But the word Munich stands out in their names and it appears that some homebrewing retailers have misclassified some special malts with Munich in their names as “Munich malt” types.

For a practical takeaway, the best way to evaluate malt for brewing, especially malts that are used for their beautiful colors and special flavors, is to taste the malt and/or prepare a malt tea using the ASBC hot steep method (or an abbreviated facsimile). Lots of great information can be quickly unveiled using malt sensory. Thanks for the terrific question!

Q I am trying to determine the necessity and benefit of a diacetyl rest in lager fermentations. I have recipes from three different homebrew suppliers; one doesn’t suggest a rest, one recommends a few days, and another recommends one week. I am brewing small (2–2.5 gallons/7.6–9.5 L) at a time. Can you shed some light on this subject?

Donnie Maheu
Baton Rouge, Louisiana

A Diacetyl rests or colloquially known as d-rests, whether brewing lagers or ales, are good insurance policies to help ward off diacetyl. Many recipes focus on wort production and provide little in the way of specific guidance when it comes to fermentation and aging. This is especially true when it comes to nuanced methods like addressing “d.” Let’s take a dip in the fermenter and look at the diacetyl story.

During metabolism, yeasts are busy converting sugars and amino acids into building blocks for new yeast cells and that cellular fuel called ATP (adenosine triphophate). Although fermentation (conversion of glucose into carbon dioxide, ethanol, and 2 molecules of ATP) is far less efficient than respiration (conversion of glucose into carbon dioxide, water, and 38 molecules of ATP), yeast cells generate sufficient energy through fermentation to build healthy and dense cell populations. Yeast cells synthesize all amino acids required for cell growth and metabolism, and along the way some of the intermediates related to amino acid synthesis escape the cell.

One of those compounds is called alpha acetolactate, a diacetyl precursor that is related to valine synthesis and valine metabolism. Skipping the biochemical details, alpha acetolactate is secreted into beer where it converts into diacetyl. Yeast can then reabsorb diacetyl, convert it into flavor-neutral compounds (butane diol and acetoin), and all is good. So why do some folks make a big deal about the diacetyl rest?

The key detail in this is the conversion of alpha acetolactate into diacetyl. The speed of this reaction varies with temperature and is accelerated by oxidants, such as oxygen and metal ions like iron. Consider a fresh bottle of beer containing alpha acetolactate. It’s a given that this diacetyl precursor is going to turn into diacetyl, but what’s not a given is how quickly the conversion will occur. If iron was picked up during beer filtration or a good gulp of air was sucked into beer during packaging, diacetyl may show up quickly. But if the beer is not filtered or bottled, a keg of cold beer containing diacetyl precursor may slowly blossom into a butter bomb over several weeks of storage. Heavily dry-hopped beers may also undergo a diacetyl spike associated with hop creep because yeast begin snacking on carbs, start producing valine, and secrete alpha acetolactate during hop creep. The takeaway is that there are several ways for diacetyl to show up in packaged beers and some paths are faster than others.

If you are cold fermenting lagers, not adding big doses of dry hops, and conduct a diacetyl rest by moving your fermenter to a room temperature environment (68 °F/20 °C) after peak fermentation is complete (usually after day five), two days is plenty. On the other hand, if you prefer to keep things simple by fermenting cold and conducting your “d-rest” cold, adding a week after primary is a good idea. And no d-rest at all is really rolling the dice. My suggestion is to use a d-rest for all styles if possible.

Q This question is short and sweet: What the heck is dip hopping?

Martin Shell
Columbia, Missouri

A Perhaps the most interesting things about dip hopping are the amount of data about the technique along with its relatively low-profile presence in the weird world of brewing hype. Before jumping into process details, let’s check out a timeline of how this method got started and introduced to US craft brewers.

In 2012, brewers from Japan’s Kirin Brewing began talking about a technique that boosts pleasant hop aromas while suppressing off-flavors. During a trip to Japan in 2014, Van Havig and Ben Love of Gigantic Brewing in Portland, Oregon visit Kirin’s Spring Valley Brewery and are struck by Spring Valley’s 496 IPL. [Consider a math geek sidebar about the meaning of 496. Some serious nerds at Kirin!!] Upon their return to Oregon, Havig and Love begin spreading the word about Spring Valley’s new method to US brewers. In 2018, Kirin presents a poster about dip hopping at the ASBC/MBAA Brewing Summit in San Diego. And last year, John Holl wrote an article about dip hopping for BYO. Seven years is a pretty long incubation period for a cool brewing technique!

Here is the skinny about the what, why, and how.

What? Hops are added to the fermenter before fermentation begins.

Why? Kirin does not explain their original idea, but it likely fell into the “why not” category. The interesting thing, which was probably old-fashioned luck, is that hop pellets accelerate fermentation and produce a different hop aroma than dry hopping later in the process.

How? The Kirin method describes slurry being pumped in line with wort during the fermenter fill.
The original Kirin method requires a few extra pieces of equipment that many smaller craft brewers lack, specifically an agitated vessel and the ability to dose a hop mixture in line with wort, but the technique is really easy to do at home because of the small scale of homebrewing. All one needs to do is add pellet hops to wort after the fermenter is filled and before fermentation begins. That’s it. Hop pellets in wort before fermentation begins. Sounds like there is something missing. Seriously, why in the heck is this so special?

Particulates in fermentation, such as activated carbon, can accelerate fermentation by reducing dissolved carbon dioxide content and boosting yeast cell density. The hop particles from dip hopping behave in a similar fashion. While interesting, this alone does not explain the aroma changes noted when dip hopping is used. But the noted reduction in onion-like flavors does reveal a real difference between dip-hopped beer versus beers dry hopped later in fermentation. Kirin’s research revealed the compound known as 2M3MB or 2-mercapto-3-methyl-1-butanol is the stinking onion.

Data published by Kirin shows that dip hopping not only reduces the concentration of dissolved carbon during fermentation, but also reduces the concentrations of myrcene (a hop aroma deemed undesirable to some brewers) and 2M3MB (via hydrogen sulfide scrubbing) compared to conventionally dry-hopped beers (Effect of Hops Addition to the Fermentation Tank on Beer Fermentation, Kirin Brewing, Tsuchiya, et al., 2018 Brewing Summit). Less myrcene and 2M3MB means that the other hop aromas can really shine, resulting in a cleaner hop aroma when hops are added in the fermenter.

I give this technique two thumbs up; so give it a try!

Issue: May-June 2022