Two-row vs. Six-row Barley:
Two types of barley are commonly malted and used to make beer. Although there are some differences between these two types they are similar enough to be consider a single species Hordeum vulgare*. The two types of barley most commonly used to make beer are referred to as two-row and six-row barley because their seeds grow along a central stem in two and six rows respectively (Figure 1). The number of seed rows depends upon the number of fertile flowers present. In the case of two-row barley only two of the six flower clusters are fertile while in the case of six-row barley all six are fertile.
Figure 1: The view looking down the axis of the stem or rachis is shown in A. A side view of the rachis is shown in B. Three clusters of flowers develop at each node of the rachis which are offset above (solid lines) and below (dashed lines). In the case of two-row barley, only the central flower at each node is fertile. As a result, one kernel would would develop at each node giving the appearance of two rows of kernels when view from above. This is the case is shown in B and is indicated by the shaded kernels in A. In the case of six-row barley, three kernels would develop at each node, thus giving the appearance of six-rows of kernels when viewed from above (Lewis and Young, 1995).
Six-row barley typically grows in relatively warm climates and is the most widely grown type of barley in the U.S. The kernel size of six-row barley tends to be quite variable whereas two-row kernels are of relatively uniform size. As a result, often times maltsters must separate the six-row barley into different size fractions prior to malting. This extra step is not, however, required during the malting of two-row barley.
Another difference between the two varieties is that six-row has greater enzymatic potential then two-row. As a result, six-row can convert more starches to fermentable sugars than two-row. A much greater percentage of relatively inexpensive adjuncts (e.g. corn or rice) can be used with six-row malt, which is why commercial breweries often use it. With six-row malt up to about 40% of the grist may be substituted with cereal adjuncts without adversely affecting the finished beer.
Although six-row barley has greater enzymatic power and produces a greater yield per acre than two-row barley there are still some advantages to using two-row. Two-row barley tends to have plumper kernels with thinner husks than six-row. As a result, two-row has a greater starch content and, therefore, can yield greater (~1-2%) extract per pound of grain.
As noted above, six-barley has thicker husks than two-row. Although the greater husk material improves the filter bed for lautering, the greater tannin content can also, if one is not careful, result in an increased astringency in the finished beer.
Six row barley has greater protein content than two-row barley. The higher protein content of six-row malt can produce haze problems in the finished beer. Six-row malt is particularly problematic in this regard because it tends to yield worts containing ample quantities of the two major contributors to haze formation (i.e. proteins and tannins); proteins present in the wort react with tannins to produce the relatively insoluble complexes responsible for haze in finished beer.
Note that although some tannins are contributed from hops the majority (~80%) of the tannins found in a typical wort are derived from the malt.
The use of six-row barley malt along with a fairly high percentage of adjuncts can help reduce both the haze and astringency problems. Not only is six-row barley less expensive per pound than two-row, its use actually requires further cost cutting through the use of relatively high percentages of inexpensive adjuncts. Six-row barley malt is the perfect choice for the American megabreweries. Keep in mind, however, that the megabreweries use far more adjuncts than absolutely necessary; beers produced with relatively large quantities of adjuncts tend to have very little body and lack much in the way of maltiness. The use of two-row malt, however, does not require the coincident use of adjuncts. Such all malt beers tend to be more complex as well as have more body. The disadvantages of both two- and six-row barley can be easily overcome; both can be used to make excellent beers.
*The classification of barley has changed over the years. This can lead to considerable confusion when doing a literature search of malting barley. During the early 20th Century two-row and six-row barley were considered to be two separate species, Hordeum distichum and Hordeum hexastichum respectively. By the 1950s, six-row barley was classified as Hordeum vulgare while two-row remained Hordeum distichum. Currently, both two-row and six-row barley are considered the same species and are classified as Hordeum vulgare (Heisel 2003, personal communication).
Note that the method of malting described in this section is that of traditional floor malting. Although it is rarely employed today it does allow one to clearly describe the various steps of the malting process. Today most malting is done in revolving drums, which eliminates the need to turn the grain/malt by hand.
The primary purpose of malting is to produce the enzymes required for mashing and to make the starches present in the raw barley more accessible to those enzymes. The initial stage in the malting process involves steeping the grain in 50-65° F (10-18° C) water for 2-4 days. During this time water is absorbed by the grain which promotes germination. The barley initially has a moister content of about 12% but this increases substantially during the steeping process. The water (preferably alkaline water) is changed frequently during this time. This is to prevent bacteria present in the barley husk from souring the water by fermenting some of the grain material. Such a reduction in pH would interfere with the development of the plant embryo. During those periods in which the barley is not submerged (i.e. between water drainage and refill), the moist barley is turned several times to promote the uptake of oxygen.
Once the water content has increased sufficiently (> 40%) the grain is spread upon the floor 8-12 inches (20-30 cm) thick. An ambient temperature of 45-60° F (7-15° C) is maintained while germination is allowed to proceed. The germinating grain must be turned and wetted frequently to dissipate the heat produced during germination and to aerate the grain. The shoot that grows beneath the husk is known as the acrospire. The acrospire grows upward from the bottom of kernel along the dorsal-side (the side opposite the crease). The endosperm is the non-living part of the kernel in which starches and other food for the embryonic plant reside. Enzymes are produced during germination and growth of acrospire so as to break down starches and proteins of the endosperm into simple sugars and amino acids that nourish the growing plant. Not all of the enzymes important to malting and mashing, however, are created during germination. Beta amylase, for example, is present in raw barley but it is in a bound form and thus, is unable to act on starch material until it is released during germination. The goal of malting is to maximize the production of useful enzymes while halting germination before the embryonic plant consumes too much food material (i.e. starches).
Protein modification is one of the most important processes to take place during germination. Starch granules comprising the endosperm are embedded in an insoluble protein-glucan matrix. Unless this matrix is broken down the action of amylase enzymes is blocked. The degree to which the protein-glucan matrix is broken down is referred to as modification. Modification is accompanied by a physical change in the grain. Prior to modification the grain is very hard or steely. After modification the grain becomes soft and friable or mealy.
Since the release of enzymes and their action is to provide food for the growing plant, modification mirrors the progress of the acrospire as it grows up the kernel. The longer the acrospire the greater the degree of modification. Of course, some of the starches are consumed by the growing acrospire so modification is, to some extent, at the expense of malt yield. The acrospire is generally allowed to grow to 2/3 to 3/4 the length of the kernel before modification is halted by kilning. It generally takes 6-10 days of growth before the acrospire reaches this length (Figure 2).
Figure 2:The progressive degree of modification which, more or less,corresponds to the growth of the acrospire is indicated by the shading. A, B and C represent the third day, the fifth day and the eighth day of germination respectively (DeClerk, 1957).
A simple method of determining the overall level of modification of a batch of malt is by means of the "sinker" test. In this test 50 kernels of malt are shaken into a pan of water. After 10 minutes the number of horizontally floating kernels is counted; undermodified kernels either sink or float vertically in the water. At the very minimum at least 35 or 70% of the kernels should float. With good malt, nearly all of the kernels should float with only two or three kernels sinking or floating vertically.
Kilning dries the malt from a moisture content of about 45-50% to about 3-5% as well as deactivates and destroys enzymes. For the initial drying of the "green" malt, the temperature is slowly raised to 90° F (32° C) and held of 24 hours. After this initial dry phase the temperature is then rapidly raised to 120° F (49° C) and maintained for about 12 hours. During this time enzymes within the grain continue to convert endosperm starches to sugars. Allowing the grain to dry before the temperature is raised above 120° F minimizes enzymatic degradation. However, the lose of some enzymes cannot be avoided. Fortunately, alpha- and beta-amylase survive at least in part. The degree to which enzymes are degraded depends upon the kilning temperature employed. Higher temperatures tend to be more destructive to enzymes. Pale and pilsner malt are generally kilned at temperatures of about 176-185° F (80-85° C) . Vienna and Munich malts are kilned at a somewhat higher temperature. They are kilned at about 185-194° F (85-90° C) and 221° F (105° C) respectively. These temperatures are not so high as to degrade the enzymes to the extent that these malts cannot be used as the basis of a recipe. The use of Munich and Vienna malt imparts body, sweetness and a slightly reddish hue to the beer. Black patent malt is kilned at about 450° F (232° C) for 2-2.5 hours. Chocolate malt is kilned at about the same temperature but for less time (1-1.5 hours). Roast barley is simply unmalted barley that has been highly roasted. The enzymes in chocolate, black patent and roasted barley have all been destroyed during roasting. These grains are used only to darken and impart a roasted or burnt flavor to the beer. Note that both chocolate and black patent malt are made from under-modified (about 50%) malt. The high temperature roasting degrades the unmodified starches so there is no need for a protein rest.
Crystal and Cara-pils (dextrin) malt are produced in a somewhat different manner in that the malt does not go through the initial drying phase. The green malt is placed in a kiln and the temperature is raised to 150-170° F (66-77° C) for 1.5-2 hours. The malt is heated without ventilation so as to prevent evaporation. During this "stewing" period the relatively high water content of the malt combined with the kiln temperature result in enzymatic reactions taking place within the individual malt kernels that are normally associated with mashing (i.e. starches are converted to sugars). This process is incomplete so not all the starches are actually converted to sugars and those sugars that are present tend to be complex and therefore, are not fermentable. After the stewing period the vents are opened and the malt is further roasted. In the case of crystal malt, the temperature is raised to at least 250° F(121° C) and the malt is roasted until the desired color is obtained. During this process the converted sugars are caramelized and the husks are darkened. In the case if cara-pils malt, after the vents are opened the roasting temperature is raised to no more than 240° F (116° C). Using crystal malt imparts sweetness as well as a reddish hue to the finished beer whereas the use of cara-pils adds body and some residual sweetness without affecting beer color.
Some brewers employ what is known as a protein rest. Two sets of proteolytic enzymes are active during the protein rest over two different temperature ranges. One set of enzymes works in the 113-122° F (45-50° C) temperature range. These enzymes convert medium sized nitrogen-based proteins into amino acids that will later be consumed by the yeast. The other set of enzymes is active from 122-144° F (50-62° C). These enzymes breakdown large proteins into forms which aid head retention and improve clarity. The traditional protein rest is carried out at a temperature of 122° F (50° C) which is a good compromise and a temperature at which both groups of proteolytic enzymes are active.
Note that in the past most malt was under modified. As a result, such malt would be relatively deficient in enzymes and the protein-glucan matrix containing the starches would not have been properly broken down during malting. During the protein rest this matrix is broken down thus making the starches more accessible to the relatively enzyme poor mash. Another result of this, of course, would be additional amino acids for yeast nutrition and improved head retention and clarity. Today, however, most malt has a high degree of modification. As such, the proteins have been sufficiently modified so that a protein rest is generally not required with today's more fully modified malts.
One final process must occur before starch conversion can take place. At temperatures of 131-149° F (55-65° C) the starch granules within the malt burst open, thus making them accessible to the action of amylase enzyme. This process is known as gelatinization and is an essential step in the mashing process. Without it very little starch conversion would take place. As the temperature of the malt is brought up to mashing temperature, the process of gelatinization takes place rapidly and, for the most part, without our even knowing it. However, in the case of rice or maize the grain must be boiled to achieve the proper level of gelatinization. Note that flaked rice and maize have been precooked so they need not be boiled prior to mash addition.
The two most important enzymes in mashing are alpha- and beta-amylase. Taken together they are known as the diastatic enzymes. Alpha-amylase works best at temperatures of 149-153° F (65-67° C). Beta-amylase, on the other hand, works best at temperatures of 126-144° F (52-62° C) . Although the temperatures given above are the optimal temperatures for these two enzymes they both work well together at 145-158° F (63-70° C) . Alpha- and beta-amylase also work best when the wort pH is in the 5.2-5.6 range.
Starches are basically long chains of glucose molecules. Alpha-amylase cleaves these chains in the middle. Until the glucose chains are reduced in size to comprise no more than three glucose molecules they will remain unfermentable. Such moderately long (four to 30 glucose molecules), unfermentable glucose chains are referred to as dextrins. The action of alpha-amylase is known as dextrinization or liquefaction.
Beta-amylase breaks bonds near the ends of the molecular chains of starches and dextrins. Beta-amylase cleaves off two sugar or glucose units from the molecular chain at a time. In doing so, beta-amylase produces fermentable sugars. That is to say, it converts starches and dextrins into maltotriose (three glucose units), maltose (two glucose units) and glucose. The action of beta-amylase is known as saccharification.
Mashing temperatures around 158° F (70° C) would favor the action of alpha-amylase. The resultant beers would be high in dextrins. Since dextrins lend body and a malty sweetness to beer, high temperature mashes would tend to produce beers that are more full bodied. On the other hand, mash temperatures of about 150° F (66° C) would favor the action of beta-amylase. Beer produced with lower mash temperatures would tend to have fewer dextrins and more fermentable sugars. Such beers would tend to be drier, less full bodied and slightly higher in alcohol.
The process of mashing is, of course, to convert starches to sugars. As one would expect maltose is the most prevalent of the wort sugars accounting for (in a typical wort) 46-50% of the wort sugars. Maltotriose comprises 12-18% of the sugars, followed by glucose at 8-10%, sucrose at 4-8%, and finally fructose at 1-2%. The remaining 12-29% is made up of minor sugars (e.g. galactose, mannose, lactose, melibiose etc.) which are not significant in themselves but taken together comprise a substantial percentage of the wort sugars.
The purpose of sparging is to rinse off as much of the sugars produced during the mash as possible. However, astringent tannins can also be extracted from the grain if one is not careful. Not only can tannins impart an astringency to the finished beer, but they also are involved in haze and beer staling. Both pH and temperature effect tannin extraction. As a rule of thumb, one should terminate the sparge when the mash pH exceeds 5.8-6.0 since higher pH values tend to increase the extraction of tannins. High sparge temperatures also increase the extraction of tannins. The critical temperature is about 171° F (77° C). Best results are obtained when the sparge is 165-167° F (74-75° C). One should also not sparge with excessive amounts of water. As a rule of thumb, one should sparge with the same amount of water as was used in the mash. The amount of sparge water used is not necessarily fixed; sparges should be discontinued when the residual extract in the spent grain approaches a specific gravity of 1.002-1.004 (0.5-1.0° B). Further sparging would tend to increase the amount of astringents present in the wort.
Malting and mashing grain are fairly involved processes. However, the malting of grain and the extraction of sugars from it are only a part of the beer-making story. It is amazing that this whole process was figured out without the knowledge and aid of modern science. I guess this says a lot for trial and error and pure blind luck. Barley can be used to make soup etc., but this somehow seems sick and perverted. The only proper use of barley is to make beer.
Daniels, R. (1995), Malting and Mashing: Rated G, Zymurgy, Vol. 18, No. 4, p. 38-42.
DeClerk, J. (1957), A Textbook of Brewing: Volume One (translated by K. Barton-Wright): Chapman & Hall, London, England, 587 pp.
Fix, G. (1999), Principles of Brewing Science,Second Edition: Brewers Publications, Boulder, CO, 189 pp.
Fix G.J. and L.A. Fix (1997), An Analysis of Brewing Techniques: Brewers Publications, Boulder, CO, 192 pp.
Forget, C. (1988), Dictionary of Beer and Brewing: Brewers Publications, Boulder, CO, 176 pp.
Heisel, S. (2003), Personal communication via e-mail on March 20, 2003 from Scott Heisel of the American Malting Barley Association.
Lewis, M.J. And T.W. Young (1995), Brewing: Chapman & Hall, London, England, 260 pp.
Miller, D. (1995), Homebrewing Guide: Story Communications, Pownal, VT, 358 pp.
Noonan, G.J. (1996) New Brewing Lager Beer: Brewers Publications, Boulder, CO, 363 pp.
Schwarz, P. and R. Horsley (1996), A Comparison of North American Two-Row and Six-Row Malting Barley: Brewing Techniques, Vol. 4, No. 6, p. 50-55. This article also appeared in its entirety in The 1997 Brewers' Market Guide published by Brewing Techniques.
As a bit of an end note, the side bar respresents a progression of increasing degrees of roasting from top to bottom. At the top is two-row malted barley followed by 80 °Lcrystal malt and then chocolate malt and finally black patent malt.
Should you have any questions or comment please e-mail Scott Stihler at firstname.lastname@example.org.