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Flavors From Malt

07/03/2013

Flavors from Malt

Originally Published By Scott Bickham Column Editor in Brewing Techniques (Volume 6, Number 5)

 

Most people can accurately describe a beer as “malty,” but beer analysts often go a step further to identify a beer as worty, husky, or having grassy notes. The differences can be subtle and not necessarily undesirable in a beer. This installment of Focus on Flavor discusses the flavors that derive from malt, including the phenolic compounds that can give your beer a medicinal flavor.

When one speaks of malty flavors, it is usually in a positive light. Medicinal, phenolic flavors are not so highly regarded, although phenolic compounds can provide subtle background flavors that would be missed if absent. Strong concentrations of any flavor can be problematic, depending on the beer style. All of these flavors derive primarily from compounds present in the first and primary ingredient, malt, but the extent of their contribution to the beer’s flavor profile is affected not only by the selection of malt but by several other factors in the brewing process.

This installment covers Classes 3, 4, and 5 of the Beer Flavor Wheel: cereal, caramel or roasty, and phenolic flavors. These flavors are listed in Table I (page 20) with their related first- and second-tier descriptors. The box “Malts and Adjuncts as Flavor Sources” on page 20 contains a summary of the flavors contributed by the most common base and specialty malts.

Cereal Flavors

The cereal flavors are classified as “grainy,” “malty,” or “worty.” Grainy is further broken down into “husky,” “corn grits-like,” or “mealy” flavors.

One way to become familiar with the husky flavors class is to chew on spent grains or to taste the last runnings from the lauter tun, particularly if six-row malt or adjuncts were used in the recipe.

Grainy flavors: Husky. These husky, grainy flavors may be regarded as either desirable or undesirable, depending on the style of the beer, the intensity of the flavor, and the personal preference of the taster. They are appropriate as a background flavor in most pale lagers, particularly the American standard and Dortmunder export styles, but they should be more subdued in the American premium, Pilsener, and Munich Helles styles. The compounds responsible for husky flavors include the aromatic aldehyde cyclopentyl methanol, which is perceived as malty, husky, or strawlike (1). Melanoidins such as 2-acetylpyridine and trimethylpyrazine contribute similar grainy flavors.

These compounds normally are present at 5–10% of their flavor thresholds, which is sufficient to make an important contribution to the background. Excessive huskiness may result from oversparging or lengthy mash schedules, particularly if the temperature and pH of the water in the lauter tun rise above the recommended ceilings of 170 °F (77 °C) and 6.0, respectively, for example. The “corn grits” descriptor is similar to the aroma of corn meal or flaked maize.

Mealy. Freshly ground grain or flour would be characterized as “mealy.” Although these comparisons are with raw materials, the flavors often carry over to the finished beer. Mealy flavors are not desirable and often result from overcrushing grains or allowing unconverted starches to pass through the lauter tun. Raw corn flavor would be appropriate in American standard lagers and cream ales that include corn grits as an adjunct, and it was probably an important component in the pre-Prohibition Pilsener style.

Malty flavors: These flavors reflect the presence of unfermented sugars, particularly maltose, maltotriose, and maltotetrose. Malty favors are favorably regarded in nearly all beer styles, with the exception of those that should be fully attenuated. Nitrogen-containing melanoidins such as the dimethyl pyrazines also contribute malty flavors.

Scott Bickham has a Ph. D. in condensed matter physics and is studying the properties of plasmas, liquid metals, and polymers at the Los Alamos National Laboratory in New Mexico. He has been home brewing and judging since 1991.

Worty flavors: These flavors are similar, but tend to have a less refined character; like graininess, they do not appeal to all tasters because they are often perceived as cloying. In small-scale brewing, they are often a sign of an abbreviated fermentation, which can occur when the yeast has depleted its supply of nutrients or has been shocked by rapid temperature changes. Worty flavors coupled with vegetal or parsnip flavors indicate contamination by Gram-negative bacteria.

Recognizing the flavors: To learn to identify cereal flavors it is best to reference the flavors and aromas of the raw materials themselves. As mentioned earlier, for example, to learn to recognize mealy flavors one has only to experience the aroma of freshly ground grain.

One can learn to recognize malty and worty flavors by tasting the wort as it is being transformed into beer. The initial profile would be characterized as worty, but this fades as sugars are consumed and the malty character becomes dominant. Worty flavors can also be produced by doctoring a reference beer. I found that 1 tbsp of an unfermented starter (specific gravity 1.035) prepared from the second runnings of a batch of Doppelbock contributed a perceptible worty, caramel flavor to a 12-oz sample of an American light lager. One tsp of malt extract syrup dissolved in 2 tsp of hot water should have a similar effect when added to the beer.

Caramelized and Roasted Flavors

The flavors in Class 4 of the Beer Flavor Wheel are classified as “caramelized/roasted,” with the first-tier descriptors “caramel” and “burnt.” Both types of flavors derive from melanoidins, which are ring-shaped, aromatic hydrocarbons. The relative levels of these basic caramel and roasted flavors are determined not only by the type of malt but also by the mashing and boiling processes. Low-temperature kilning and simple mashing procedures favor the production of melanoidins with bready or biscuitlike flavors, which are desirable in most beer styles. More intensive thermal loading during malting produces more of the toffee and toasted malt character found in many dark German lagers. Finally, the high kilning temperatures used to make roasted malts produce flavors that are described as bitter chocolate, burnt, and even smoky. Burnt flavors can also originate from scorched grains in mashes that are not properly stirred, but the relatively low density of wort prevents roasted flavors from being formed during the boil. Nevertheless, direct firing of brew kettles and low-flow external wort boilers can impart distinct caramelized flavors to wort.

Caramel flavors: These flavors are broken down into the descriptors “molasses” and “licorice,” which should be familiar to most tasters. Melanoidins with these flavors are formed through the reaction of reducing sugars with secondary amines, such as pyrrolidine, which is formed from the decarboxylation of proline (a primary amine) (2). Crystal malt contains more of these compounds than pale malt, but most are below their individual thresholds in the finished beer, with the exceptions of maltol and iso-maltol. Another member of this family, pineapple furfural, has burnt sugar and (not surprisingly) pineapple flavors (1). In the Meilgaard flavor-unit system, these caramel flavors are acceptable as primary flavor constituents in some specialty beers, particularly dark ales. In fact, licorice and molasses are often used as adjuncts in porters and imperial stouts to accent these characteristics. Also, molasses flavors often develop in ales upon aging, in conjunction with sherrylike flavors. These flavors are appropriate in old ales, barleywines, and imperial stouts.

Table I: Malt-Derived Flavors in Beer*

First Tier

Second Tier

Perception†

Comments, reference compound

Class 3: Cereal

0310

Grainy

O,T

Raw grain flavor

0311

Husky

O,T

Husklike, chaff

0312

Corn grits

O,T

Maize grits, adjuncty

0313

Mealy

O,T

Flour

0320

Malty

O,T

Maltose

0330

Worty

O,T

Fresh wort, used in conjunction with other terms to describe infections

Class 4: Caramelized, roasted

0410

Caramel

O,T

Burnt sugar, toffee

0411

Molasses

O,T

Molasses, black treacle

0412

Licorice

O,T

Brewers’ licorice

0420

Burnt

O,T,M

Scorched aroma, dry mouthfeel, sharp, acrid taste

0421

Bread crust

O,T,M

Charred toast

0422

Roast barley

O,T,M

Roasted malt/barley

0423

Smokey

O,T

Smoky

Class5:Phenolic

0500

Phenolic

O,T

Phenolic

0501

Tarry

O,T

Asphalt, pitch

0502

Bakelite

O,T

Plasticlike, Band-Aid

0503

Carbolic

O,T

Charcoal

0504

Chlorophenol

O,T

Hospital-like, trichlorophenol

0505

Iodoform

O,T

Iodophors, hospital-like, medicinal

*Information from reference 2, pp. 467–468.

†Perception key: O = odor, T = taste, M = mouthfeel

         

Burnt flavors: The burnt flavors have the second-tier descriptors “burnt toast,” “roast barley,” and “smoky.” These flavors are primarily from nitrogen-containing melanoidins in the pyrazine and pyridine groups, in contrast to the bready/biscuit flavors in pale malt, which arise primarily from sulfur-containing melanoidins. Pyrazines and pyridines are prevalent in roasted barley and in chocolate and black malts, and they give stouts and porters their dark colors and distinctive flavors. Excessive amounts of these malts often result in a burnt, charred aftertaste, however, so the key to brewing these styles is balance and moderation. Even then, stouts and porters usually have a dry, slightly acrid mouthfeel that is unpleasant to some tasters. It is also important to differentiate these roasty flavors from the carbolic burnt flavors of some phenols, but this distinction is often difficult when evaluating a dark beer with fermentation flaws.

Malts and Adjuncts as Flavor Sources

Base malts: The base malts used in brewing are predominantly produced from six-row or two-row barley, with the latter subdivided into pale lager, or Pilsener, malt and pale ale malt. Pilsener and six-row malts are generally not fully modified and are kilned at relatively low temperatures (around 140 °F [60 °C]), whereas pale ale malt is fully modified and kilned at slightly higher temperatures. Thus pale ale malt produces a darker beer with some caramel and biscuitlike or bready flavors. Six-row malts have a higher percentage of husk material than two-row malts. Because most of the phenolic compounds in malt originate in the outer layers of the kernel, which includes the husk, beer produced from six-row malts tends to have higher levels of phenols than beer from two-row malts.

Specialty malts: In addition to these base malts, brewers use a wide range of specialty malts and adjuncts to provide additional flavor and color. The most common group comprises caramel malts, which are kilned at 140–170 °F (60–77 °C) while moist to saccharify the starches inside the kernel. This process extensively degrades proteins and increases the malt’s acidity. After the starches have been sufficiently converted, the malt is heated in torrefaction (parching) drums to develop the flavor and color. The resulting malt varies from cara pils, which has a very light color of 2 °L, to dark crystal, with a color of 80 °L or higher.

Munich and Vienna malts are produced by cycling hot, humid air through the kiln, which partially converts some of the starches into reducing sugars. These sugars combine with amino acids through the Maillard reaction to produce the melanoidins that give these malts their characteristic biscuitlike or bready flavors. Melanoidin formation has been discussed in detail elsewhere (7,8), but it should be noted that this reaction will continue during the mashing and boiling stages of beer production.

Another group of malts relevant to the flavors discussed here are roasted malts such as chocolate and black patent, which are produced by kilning the malts at a series of increasing temperatures. These malts have distinctive bitter chocolate, burnt, or roasty flavors and darken the beer considerably. The roast barley used in stouts is made in a similar manner, but it is not malted. Smoked malts are still being produced using the traditional method of kilning over hardwood or lignin. Not only do these malts absorb lignin phenolics from the burning fuel, but also some of the native phenolic compounds in the husk may be chemically transformed by the heat (3).

Adjuncts: Several adjuncts are also used to provide caramel or roasted flavors to beer. Caramel syrups are produced by caramelizing sucrose or starch syrups with a high glucose content (1). Ammonia is sometimes used to increase the yield of this process, but this results in the formation of 4-methylimidazole, which is toxic to some animals. Malt-based colorant is also produced by conventionally mashing roasted malt and then concentrating the wort into a syrup similar to the process used to manufacture malt extract. Other adjuncts that impart these types of flavors are molasses, treacle (a blend of molasses, invert sugar, and corn syrup), and brown sugar.

Recognizing the flavors: To become familiar with these flavors, one should taste as many different types of roasted and caramel malts as possible. It is also possible to produce these flavors in a reference beer by adding a tablespoon of a melanoidin-rich wort starter to a 12-oz sample of reference beer, as described in the malty/worty section. Caramel and molasses flavors may also be produced by dissolving 1 tsp of dark corn syrup or molasses into 1 tbsp of hot water and adding the resulting mixture to the reference beer. (This experiment will require the removal of about half an ounce of liquid to make room for the adulterant.) These amounts were sufficient for my palate, but your mileage may vary.

Phenolic Flavors

The last class of flavors contributed by malt are phenolic flavors, which were discussed in detail in Steve Alexander’s recent BT article, “Fear of Phenols: A Guide to Coping with Brewing’s Most Contrary Chemicals” (3,4). Alexander provided an excellent introduction to the origins, chemical structure, and flavoring effects of phenols in beer. The information here complements that article, focusing on the most common phenolic flavors and identifying their probable origins in the brewing process.

The phenolic class of the Beer Flavor Wheel is broken down into “tarry,” “Bakelite,” “carbolic,” “chlorophenol,” and “iodoform,” descriptors as shown in Table I on page 20. Other common descriptors are “medicinal,” “clove,” “Band-Aid, “and “electrical fire,” so phenols clearly can produce a wide spectrum of flavors. Although the descriptors on the Beer Flavor Wheel were designed to be familiar to most tasters, “Bakelite” may need some clarification. It refers to a plastic developed in the 1920s that is used to make a variety of products ranging from costume jewelry to capacitors. It produces a slightly smoky, plastic- or Band-Aid-like aroma when cut or sanded, so these descriptors might be more useful.

Although these descriptors all sound negative, it should be noted that beers that had been stripped of all phenols were formed to be dull-tasting by a taste panel (5). Thus, when phenols remain in the background, they contribute positively to beer flavor.

Phenols from malts: The primary source of phenolic compounds in beer is malt, although most of these compounds can be released only through mashing (5). For this reason, intensive mashing procedures such as triple decoctions favor the release of more phenols into the wort, although usually at levels well below the flavor threshold.

Table II: Troubleshooting Cereal, Caramel, Roasty, and Phenolic Flavors

Flavor

Cause

Origin/Remedy

Grainy

Oversparging, alkaline or hot sparge conditions

Reduce sparge volume, pH, or temperature.

Corn grits

Too much corn-based adjunct

Reduce amount used.

Mealy

Overcrushing grain, starch in wort

Coarser crush, more thorough mash procedure.

Malty

Too much malt, high saccharification temperature

Reduce malt and saccharification temperature.

Worty

Abbreviated fermentation

Raise fermentation temperature, repitch yeast, or add yeast energizer.

Excess caramel

Excessive use of caramel malts

Reduce caramel malts.

Excess roast

Excessive use of roasted malts, scorched mash

Reduce roasted malts, monitor and stir mash.

Medicinal, plastic, smoky

Phenolic compounds, usually from wild yeast

Obtain fresh yeast and watch sanitization.

Chlorophenol, iodophor

Reaction with sanitizers

Rinse thoroughly, avoid using plastic and rubber hoses or fermentors immediately after sanitizing.

Oversparging and sparging with alkaline water also promote the extraction of phenols from the grain husks. It has also been shown that the extraction of phenols from malt also depends strongly on the malt-to-water ratio. Worts produced from thin mashes with a ratio of 1:4 and 1:5 contain higher levels of phenols than those produced from more concentrated mashes with a ratio of 1:3, which is equivalent to 1.5 quarts of water per pound of malt (5). Some common phenols found in wort are hordenine, 4-vinyl guaiacol, vanillin, and syringaldehyde, catechin, and epicatechin. These compounds are formed by the thermal breakdown of phenol–carboxylic and hydroxycinnamic acids, and although vanillin and syringaldehyde are metabolized by yeast, the others are carried over to the finished beer (2).

Phenols from hops: Phenolic compounds from hops primarily include phenolic acids, proanthocyanidins, and flavonols, but the amount of hops used is small compared to malt, and the phenolic compounds contributed are thus minimized (5). This implies that these phenolic acids do not precipitate nor are they metabolized by yeast, but their contribution to the overall phenol level is still generally insignificant compared with compounds derived from malt.

Effects of fermentation: Although the phenols in beer primarily originate in the malt, the flavor levels can change dramatically during the fermentation process. This fact is particularly true with ales, since many top-fermenting strains are capable of decarboxylating cinnamic acids to produce the more flavor-active phenols (3). In particular, the Saccharomyces cerevisiae strains used for Weizens produce extremely high levels of 4-vinyl guaiacol, which has clovey notes. Vanilla is another phenolic-based flavor that is commonly encountered in Weizens, and some Scottish-ale yeast strains are also reputed to produce low levels of smoky phenols.

Some wild yeast strains and, less frequently, enteric bacteria, produce high levels of less desirable phenolic flavors. Bakelite or plasticlike flavors are usually attributed to phenol, cresol, and 4-vinyl phenol, whereas isoeugenol is described as “dental antiseptic” or clovelike (1). Other phenols such as 4-ethyl syringol and 4-vinyl syringol have smoky characteristics. These contaminants also produce high levels of polyphenols, which are linked chains of phenolic rings that have very little aroma, but produce an unpleasant, mouth-puckering astringency.

Reactions with sanitizers: Another common source of phenolic flavors is the interaction of wort or beer with sanitizers, particularly those containing chlorine or iodine. This reaction generally results in chlorophenols, which have a disinfectant-like, medicinal flavor, and iodine-containing phenols have very similar characteristics. Although one can usually detect these compounds at concentrations as low as 5 ppb, a significant percentage of the population is completely insensitive to this flavor (6). Chlorophenols are readily absorbed by fermentors and hoses and passed on to the beer as it is being transferred, so these materials should be thoroughly rinsed and aerated after contact with sanitizers.

Recognizing the flavors: Several of these phenolic flavors can be used to doctor a reference beer. An excellent sample can be prepared by adding 0.4 mL of Vicks Chloraseptic mouthwash to a reference beer, which is approximately equivalent to adding 1/3 tsp of solution of ⅛ tsp Chloraseptic plus ⅜ tsp distilled water to a 12-oz sample. Although the source of the clovelike flavors in beer is 4-vinyl-guaiacol, this compound is not readily available. An alternative that comes close is to use actual cloves; I found that adding 4 tsp of a solution prepared by soaking several cloves in 3 oz of beer was sufficient to doctor a 12-oz sample of a reference beer. Although artificial vanilla extract will give vanilla flavors, the ethanol in the solution may compromise the tasting experiments. The chlorophenol and iodophor flavors are not as easy to reproduce because they require the chemical interaction of the sanitizer and phenolic compounds in the beer, but it usually takes only one encounter with them in an affected beer to sensitize one’s palate to these objectionable flavors.

Good and Bad Malt Flavors

The cereal flavors discussed here are a result of using grains in the brewing process and are therefore appropriate in most styles. Caramel and roasty flavors are also malt-based, but according to the Meilgaard flavor unit system, they are usually found at significant levels only in specialty beers. This includes a significant number of styles, including most ales and amber and dark lagers. Although some phenols are desirable in beer as a background constituent, the perceptible levels of the flavors covered here usually indicate problems in the brewing process that should be addressed. Tips for troubleshooting inappropriate levels of these flavors can be found in Table II on page 22.

Next Stop

In the next revolution of the Beer Flavor Wheel, we will characterize the last class of malt-derived flavors, which includes those categorized as “grassy,” “green,” or “nutty.” Also in this class are resinous flavors, which will enable us to make a transition to hop-derived flavors and finally to alcohols and esters. We will then turn our attention to aromatic compounds either derived from hops or produced in the fermentation process.

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