MBAA TQ
vol. 49, no. 1
• 2012 • pp. 19–24
Effect of Storage and Its Impact on Some Parameters Used in Assessing Distilling Wheat Cultivars R. C. Agu* and J. Walker The Scotch Whisky Research Institute, Research Avenue North, Riccarton, EH14 4AP, Scotland, United Kingdom
ABSTRACT
SÍNTESIS
Wheat varieties of distilling quality were grown at two locations where different nitrogen fertilizer treatments were administered. Relationships between parameters used to assess wheat quality for Scotch whisky grain distilling such as moisture, nitrogen, hardness, and alcohol yield were assessed after harvest and reassessed after one year to determine the effect storage had on wheat quality. Changes observed in these parameters affected wheat quality in different ways. An increase in average wheat alcohol yield (dry weight basis [dwb]) of 1.6% was found for wheat grown at the lower nitrogen site. These samples had a higher average moisture level at harvest, and showed greater moisture loss (average = 8.7%) during storage. In contrast, a decrease in average wheat alcohol yield (dwb) of 0.6% was observed for wheat grown at the higher nitrogen site. This set of wheat samples had lower moisture levels at harvest, and lower moisture loss (4.1%) after storage. Both sets of wheat showed marginal increases in total nitrogen content which ranged from 0.01–0.12% for lower and 0.01– 0.08% higher nitrogen wheat. When the harvest and stored data was compared, weak correlations for oven moisture (R = 0.2766) and grain hardness (R = 0.1789) were found for wheat varieties grown at the lower nitrogen site, while stronger correlations were observed for moisture (R = 0.6573) and hardness (R = 0.8403) for wheat grown at the higher nitrogen site over the same period. The lower nitrogen wheat, which showed a greater loss of moisture during storage, showed a strong correlation for NIR nitrogen (R = 0.9269) compared to wheat grown at the higher nitrogen site (R = 0.7652). Changes observed for moisture, nitrogen, and hardness of stored wheat appeared to have little effect on alcohol yield. Correlation results for alcohol yield assessed before and after storage for lower nitrogen (R = 0.8616) and higher nitrogen wheat (R = 0.8814) were similar and shows that storage did not have a dramatic effect on wheat alcohol yield. This observation has important commercial value because it demonstrates that storage of wheat does not have a detrimental effect on alcohol yield when such wheat is processed for alcohol production. Keywords: Wheat, nitrogen, hardness, residue viscosity, alcohol yield, storage
Se cultivaron variedades de trigo para la destilación de alcohol en dos suelos tratados con diferentes fertilizadores a base de nitrógeno. Después de la cosecha se compararon diferentes parámetros (como humedad, nitrógeno, dureza, y rendimiento de alcohol) usados para evaluar la calidad de trigo para elaborar whisky Escocés; fueron reevaluados al año para determinar los efectos del almacenaje sobre la calidad del whisky. Variaciones en los parámetros testados afectan la calidad del trigo de diferentes maneras. Se observó un aumento en el rendimiento (base seco) promedio de alcohol de 1,6% en el trigo cultivado con menor tasa de nitrógeno. Este trigo tuvo una mayor humedad al cosecharlo y mostró la mayor pérdida de humedad (media = 8,7%) durante el almacenaje de un año. A diferencia de esto, el trigo con mayor tasa de nitrógeno tuvo una reducción en el rendimiento (base seco) promedio de alcohol de 0,6%, como también una menor humedad al cosecharlo y menos pérdida de humedad (4,1%) durante el almacenaje. Las muestras de las diferentes variedades de trigo mostraron ligeros aumentos en el contenido de nitrógeno durante el almacenaje, de 0,01–0,12% para la de menor contenido de nitrógeno (en el suelo) y de 0,01–0,08% para la de mayor contenido. Al comparar los datos para el trigo recién cultivado y el almacenado, se notó una baja correlación para humedad (R = 0,2766) y para dureza del grano (R = 0,1789) para las variedades del sitio de bajo contenido de nitrógeno, mientras que para los trigos cultivados en los sitios con mayor contenido de nitrógeno tuvieron mayores correlaciones para humedad (0,6573) y para dureza (R = 0,8403). El trigo del sitio con menor nitrógeno, y mayor pérdida de humedad durante el almacenaje, tuvo una fuerte correlación (R = 0,9269) para su nitrógeno NIR (“near infra red”), comparado con el otro trigo (R = 0,7652). Las variaciones observadas en cuanto a la humedad, nitrógeno y dureza durante el almacenaje tuvieron poco efecto sobre el rendimiento de alcohol. Las correlaciones para el rendimiento de alcohol antes y después del almacenaje fueron muy similares para los trigos de los dos sitios, (R = 0,8616) para el de menor nitrógeno y (R = 0,8814) para el de mayor, y demuestra que el almacenaje no tiene un efecto dramático sobre el rendimiento de alcohol. Esto tiene una gran importancia comercial, pues demuestra que el almacenaje de trigo no tiene un efecto negativo sobre el rendimiento de alcohol en trigos específicamente cultivados por su producción de alcohol. Palabras claves: Almacenaje, dureza, nitrógeno, rendimiento de alcohol, trigo, viscosidad residual
Reginald Agu obtained a B.S. degree in industrial chemistry in 1980 and an M.S. degree in brewing science and technology in 1985 from the University of Nigeria, Nsukka. He obtained his Ph.D. degree at Heriot-Watt University in the United Kingdom in 1997. Agu worked with G. H. Palmer at Heriot-Watt University on the Cereal (Barley) Research Project for the Home Grown Cereal Authority (HGCA) UK. Agu is currently a cereal research scientist at The Scotch Whisky Research Institute, Edinburgh. He has a good knowledge of different cereals, including barley, maize, millet, sorghum, and wheat.
Introduction Wheat is the major cereal used by the Scotch whisky industry for the production of grain whisky. Maize was previously used but was replaced as the main raw material by wheat over two decades ago. Winter wheat varieties are the preferred cereal for the production of Scotch grain whisky and the yield of alcohol produced by a distillery is dependent on the quality of wheat used in the process. Distilling wheat is typically characterized by “soft” grain with a starchy endosperm and low total nitrogen level. Extensive work has been carried out on wheat at the Scotch Whisky Research Institute (SWRI) in collabora-
*Corresponding author. E-mail:
[email protected] doi:10.1094 / TQ-49-1-0316-01 © 2012 Master Brewers Association of the Americas
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vol. 49, no. 1
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tion with plant breeders. This investigation has focused on the alcohol yield performance of different wheat varieties obtained during the annual wheat harvest. Results obtained over the years have not only increased our knowledge of wheat physiology, they have also enabled the development of wheat varieties capable of producing high alcohol yields. For example, grain nitrogen and grain hardness have been shown to have a combined influence on alcohol yield from U.K. soft winter wheat (7). Work has also been carried out on various aspects of wheat processing (4,6,7) during this time. Although our knowledge of wheat physiology has increased over the years, full knowledge of wheat as a substrate and its behavior during processing continues to expand due to the complex range of factors that influence characteristics of wheat and wheat processability. One of the most important factors influencing the quality of wheat used for distilling is the protein or total nitrogen content of the grain. There is a well-established significant inverse relationship between grain nitrogen and alcohol yield (12). Also the level, composition and structure of starch and non-starch polysaccharides, for example β-glucans and other cell wall materials are important parameters that will affect the processability of wheat. Nonstarch polysaccharide (NSP) substrates present in wheat have not been systematically investigated. Protein is known to be a major factor in determining wheat distilling quality in terms of alcohol yield (5,7,10,15,16,17,18,25–28) and the inverse relationship between starch and protein (1,2,12) has also been recognized. The precise interactions between protein, starch, and other substrates that influence both the processing properties and the alcohol yield obtained from wheat are unclear. It is, however, believed that these may relate to the structure (spatial orientation) and interaction between and among the protein matrix embedding the starch granules, as well as the nature, composition, and interaction of other substrates such as cell wall materials. Swanston et al. (26) noted that grain nitrogen content was strongly influenced by the environment and that starch content did not always correlate well with alcohol yield, an observation that was further confirmed by other studies (5,17). Later research (7) showed that apart from the well documented relationship between starch and protein in terms of wheat processability and alcohol yield, grain hardness also played an important role in improving wheat alcohol yield. These observations imply that very complex relationships exist between the various substrates present in cereals. These relationships can also be influenced to some extent by the orientation (structure and conformation) of the different substrates, which may influence the complex interactions among them. These interactions could result in the formation of substrates such as glycoproteins and glycolipids and could affect the accessibility of wheat starch and non-starch polysaccharides during processing. In some cases, the stereochemistry of these substrates will also render the molecules highly susceptible to hydrogen bonding, which will have an important influence on the release of starch during processing (19) as extra energy would be required to break hydrogen bonds. There is very strong evidence showing the involvement of water in carbohydrate-protein binding (14), apart from the internal hydrogen bonding existing between substrates (9). A hydrogen bond is the attractive interaction of a hydrogen atom with an electronegative atom, such as nitrogen or oxygen, that comes from a molecule or chemical group (23). This type of bonding could lead to the formation of water, which will affect alcohol yield due to its interactions with proteins,
Effect of Storage on Wheat
starch, and non-starch polysaccharides impacting on starch hydrolysis to produce fermentable sugars. Although the relationship between alcohol yield and protein (nitrogen) is well documented, and the role that grain hardness plays in relation to wheat alcohol yield has been reported (7), it is not known how storage of wheat after harvest will affect the different parameters used in assessing wheat quality, such as the relationship between grain nitrogen and alcohol yield. This is important in view of the fact that wheat may be stored for prolonged periods in a warehouse for various reasons including abundance of grain after a good harvest. How storage will affect the processing characteristics of wheat is unknown at present. In this study, ten varieties of winter wheat, grown at two different nitrogen sites (lower and higher nitrogen sites) in the U.K., were assessed immediately after harvest. The samples were stored in tightly sealed, screw-top plastic containers for one year and then reassessed. Important and interesting changes were observed and the results obtained are reported in this paper.
Materials and Methods Wheat Samples Ten (10) wheat varieties each grown at two locations in the U.K. in 2009 were used in this study. Since the growing conditions and wheat varieties were similar, what varied was the growing environment (8). One location was a higher nitrogen/fertilizer application growing site while the other was a lower nitrogen/fertilizer application growing site. After harvest in 2009, the samples were assessed immediately for alcohol yield. The samples were then stored in tightly sealed plastic containers at laboratory temperature (approximately 20°C) for a period of one year, after which they were reassessed.
Nitrogen and Grain Hardness Determination Wheat samples were run through the NIR analyzer using the FOSS Infratec 1241 Grain analyzer (Foss Tecator AB, HOGNAS, Sweden) using a U.K. Grain Network wheat model immediately after harvest and after one year of storage. The NIR instrument analyzes subsets of sample (10 aliquots) before registering an average output reading. Parameters measured by the NIR instrument include moisture, protein (dry weight basis [dwb]), and grain hardness. Total nitrogen (dwb) of wheat was obtained by dividing the protein value by a standard conversion factor of 5.7, which is used specifically for wheat as opposed to the conventional conversion factor of 6.25 employed for barley (11,20).
Alcohol Yield Analysis The method was based on Brosnan et al (12), which simulates the production process conditions used in a “typical” Scotch whisky grain distillery. Details of this method have been described in a previous communication (6). In brief, cereal flour (30 g) obtained by milling the grains in a Buhler Miag disc mill (setting 0.2 mm) was transferred into a stainless steel mashing beaker and slurried with water (81 mL) and 25 µL of Termamyl 120 L (a fungal α-amylase supplied by Novozymes France S.A.). The contents of the beaker were gradually heated to 85°C in a water bath, before pressure cooking at 142°C for 15 minutes in a multi-control 12 L programmable CertoClav autoclave (CertoClav Sterilizer GmbH, A-4050 Traun/Austria). The cooked slurry was cooled to 85°C and given a second treatment with Termamyl (25 µL) and then
MBAA TQ
Effect of Storage on Wheat
mashed at 65°C for 1 hour with a calculated amount of high enzyme grain distilling malt grist (Miag setting 0.2 mm). After cooling to room temperature, the mash was pitched with distillers yeast (Kerry M-Type yeast supplied by Kerry Ingredients & Flavours). The mash was then fermented at 30°C for 68 h and distilled to collect the alcohol. The alcohol yield was determined from the alcohol strength of the distillate, using a Paar 5000 density meter. The alcohol yield (PSY) is quoted as liters of alcohol per tonne of wheat (LA/tonne) on a dry weight basis.
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in average NIR nitrogen than the wheat samples grown at the higher nitrogen site. Since nitrogen measurements were performed using the NIR instrument, which measures changes in dipole moments resulting from absorption of energy and overtones associated with the functional groups present in a compound and giving characteristic spectra (22), it is not clear from this study how changes in moisture content before and after storage of wheat will affect the vibration/rotational energy associated with atoms present in these molecules (samples). There is compelling evidence, however, to show that water has a very strong NIR response for nitrogen (21). However, this was not investigated, as the major interest in this study is on the impact that loss of moisture content of stored wheat, with the corresponding observed changes in NIR nitrogen content will have on alcohol yield obtained from stored wheat, bearing in mind the wellestablished inverse relationship that exists between grain nitrogen and starch and by extension, alcohol yield. Although the increase in NIR nitrogen appeared to be marginal, it made some impact on the results of this study and is discussed below. In a study with barley, Agu and Palmer (3) showed that a 0.2% difference in protein nitrogen content (same barley variety) was enough to make a significant difference in extract recovery from malted barley. In this regard, it is important to note that in this study, the changes observed for moisture and/or nitrogen and their impact on alcohol yield is immediately seen in the average PSY results shown in Table 1 and are discussed in more detail below. In Table 1, it can be seen that a 1.6% increase in average alcohol yield was observed when the wheat varieties, grown at the lower nitrogen site, were reassessed in 2010 compared with alcohol yield values obtained when the same samples were first assessed after harvest in 2009 (details shown in Table 2). In contrast, a decrease in average alcohol yield of 0.6% (Table 1) was observed for the same wheat varieties grown at the higher nitrogen site when reassessed in 2010 compared with average alcohol yield values obtained in 2009 (details shown in Table 3). Detailed PSY results (Table 2) for the individual wheat varieties grown at the lower nitrogen site, when re-analyzed in 2010, gave an increase in alcohol yield ranging from 3 to 13 LA/t (dry basis) when compared with alcohol yield results obtained in 2009. For this set of wheat samples,
Residue Viscosity Residue viscosity is a measure of the potential for processing problems arising from handling the distillation residues (spent wash co-products). Details of this determination were described previously (6).
Results and Discussion The wheat varieties studied were grown at two different sites in the United Kingdom, harvested, and first analyzed in 2009, then stored in tightly sealed plastic containers. After a storage period of one year, the samples were re-assessed using the same methods used originally. The aim was to assess what has changed during the storage period. The average analytical results obtained in 2009 and 2010 for the wheat quality parameters measured (oven moisture, NIR total nitrogen, and predicted spirit yield [PSY]) are shown in Table 1. Results show that for both sets of wheat varieties grown at the two different sites, a decrease in average oven moisture was observed when the samples were re-assessed in 2010, even though the samples were stored in tightly sealed plastic containers. The results in Table 1 further showed that the wheat samples grown at the lower nitrogen site, which had a higher average moisture content in 2009, showed greater moisture losses during the next 12 months, whereas the wheat samples grown at the higher nitrogen site with lower average moisture content in 2009 showed lower percentage losses in moisture content in 2010. In contrast to the moisture data, a marginal increase in average NIR nitrogen content of wheat was found after one year of storage, with the wheat samples grown at the low nitrogen site showing slightly higher percentage increases Table 1. Average results of some parameters measured.
NIR total nitrogen (%) dry
Oven moisture (%)
PSY (LA/t) dry
Site
2009
2010
Difference (%)
2009
2010
Difference (%)
2009
2010
Difference (%)
Site 1 lower nitrogen site Site 2 higher nitrogen site
13.96 12.51
12.75 12.00
8.7 4.1
1.34 1.69
1.39 1.72
3.6 1.7
460.71 463.05
468.07 460.33
1.6 increase 0.6 decrease
Table 2. Results obtained for oven moisture, NIR nitrogen and alcohol yield for the lower nitrogen site. Oven moisture (%)
NIR nitrogen (%) dry
Alcohol yield (LA/t) dry
Wheat variety
2009
2010
Difference
2009
2010
Difference
2009
2010
Difference
Claire Beluga Cassius Edmunds Glasgow Invicta Robigus Scout Viscount Warrior
14.51 14.26 14.06 14.11 13.87 13.96 14.05 13.68 13.45 13.62
12.77 12.97 12.67 12.61 12.80 12.85 12.68 12.73 12.64 12.79
–1.77 –1.29 –1.39 –1.50 –1.07 –1.11 –1.37 –0.95 –0.81 –0.83
1.48 1.37 1.30 1.29 1.30 1.32 1.19 1.44 1.26 1.40
1.50 1.41 1.35 1.38 1.33 1.33 1.31 1.50 1.32 1.42
0.02 0.04 0.05 0.09 0.03 0.01 0.12 0.06 0.06 0.02
460.83 471.81 458.78 453.39 462.45 462.13 464.53 456.46 467.46 449.23
463.74 477.39 466.88 465.61 471.54 467.03 468.83 462.41 475.30 461.94
2.91 5.58 8.10 12.22 9.09 4.90 4.30 5.95 7.84 12.71
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Effect of Storage on Wheat
Table 3. Results obtained for oven moisture, NIR nitrogen and alcohol yield for the higher nitrogen site. NIR nitrogen (%) dry
Oven moisture (%)
Alcohol yield (LA/t) dry
Wheat variety
2009
2010
Difference
2009
2010
Difference
2009
2010
Difference
Claire Beluga Cassius Edmunds Glasgow Invicta Robigus Scout Viscount Warrior
12.43 12.62 12.44 12.72 12.48 12.56 12.49 12.53 12.42 12.44
12.09 12.03 11.92 12.23 11.99 12.06 12.02 11.90 11.98 11.81
–0.34 –0.59 –0.52 –0.49 –0.49 –0.50 –0.47 –0.63 –0.44 –0.63
1.72 1.67 1.72 1.71 1.71 1.70 1.66 1.75 1.59 1.68
1.78 1.67 1.70 1.72 1.69 1.74 1.68 1.78 1.63 1.76
0.06 0.00 –0.02 0.01 –0.02 0.04 0.02 0.03 0.04 0.08
458.94 470.73 462.30 460.75 466.01 465.49 466.06 461.53 470.30 448.41
461.34 465.59 462.03 454.91 459.70 460.06 464.59 457.20 469.12 448.71
2.40 –5.14 –0.27 –5.84 –6.31 –5.43 –1.47 –4.43 –1.18 0.30
Table 4. Correlation between 2009 and 2010 for oven moisture, hardness, total nitrogen, predicted spirit yield, and residue viscosity. Parameter
Site
Oven moisture
Site 1 Lower nitrogen site Site 2 Higher nitrogen site Site 1 Lower nitrogen site Site 2 Higher nitrogen site Site 1 Lower nitrogen site Site 2 Higher nitrogen site Site 1 Lower nitrogen site Site 2 Higher nitrogen site Site 1 Lower nitrogen site Site 2 Higher nitrogen site
Hardness Total nitrogen Predicted spirit yield Residue viscosity
R 0.2766 0.6573 0.1789 0.8403 0.9269 0.7652 0.8618 0.8814 0.6657 0.5970
an increase in wheat nitrogen content ranged from 0.01 to 0.12% (dry basis), or from 0.06 to 0.68% protein nitrogen. In contrast, detailed PSY results for the individual wheat varieties grown at the higher nitrogen site (Table 3), when re-analyzed in 2010, gave a decrease in alcohol yield ranging from 1 to 6 LA/t (dry) when compared with alcohol yield results obtained in 2009. For this set of wheat samples, an increase in wheat nitrogen content ranging from 0.01 to 0.08% (dry basis), or 0.06 to 0.46% protein nitrogen, was also found. These results are very complex and difficult to explain. It is, however, important to observe from the results in Table 1 that the average percentage loss in moisture (8.7%) as well as the average percentage gain in nitrogen content (3.6%) was twofold for the wheat samples grown at the lower nitrogen site compared with those observed for wheat samples grown at the higher nitrogen site, for which 4.1% and 1.7%, respectively, were found. These changes in wheat moisture and nitrogen content are likely to have affected the PSY results shown in Tables 2 and 3. Apart from the compelling evidence that water has on NIR response for nitrogen (21), there is also strong evidence of involvement of water in carbohydrate-protein binding (14). In this regard, changes in moisture and nitrogen content of wheat may affect the initial structural orientation of carbohydrate and protein substrates present in these cereals, as well as re-orientation of these substrates following loss of water (moisture) during storage because both macro-molecular substrates are actively involved in hydrogen bonding, although in different ways. A closer look at the effect storage had on wheat grown at the lower nitrogen site revealed a very weak correlation for oven moisture (R = 0.2766) and grain hardness (R = 0.1789) (Table 4). Wheat samples grown at this site gave higher percentage moisture loss over the one year storage period (Table 1). In contrast, a much stronger correlation was found for oven moisture (R = 0.6573) and grain hardness (R = 0.8403) for samples grown at the higher nitrogen site (Table 4). These samples
grown at the higher nitrogen site gave much lower percentage losses of moisture (Table 1). It would appear from these results (Tables 1 and 4) that while lower nitrogen wheat samples studied appeared to have a higher propensity to lose more moisture during storage, they showed a poor correlation for grain hardness. Conversely, while higher nitrogen wheat showed a lower propensity to lose moisture during storage, they gave stronger correlation results for grain hardness. These results in Table 4 suggest that moisture loss in wheat during storage had a lesser effect on grain hardness for lower nitrogen wheat, and more effect on grain hardness of higher nitrogen wheat (Table 4). These results agree with studies by Brown et al. (13) who observed a linear relationship between hardness and grain moisture for hard but not soft wheat varieties. Results for NIR nitrogen reported in Table 1, as well as the very strong correlation (R = 0.9269) obtained for NIR nitrogen in 2009 versus 2010 of wheat samples grown at the lower nitrogen site (Table 4) when compared with lower but strong correlation results (R = 0.7652) obtained for NIR nitrogen in 2009 versus 2010 of wheat samples grown at the higher nitrogen site (Table 4) are interesting, but further studies are required to confirm these observations. Other interesting results for wheat grown at the different nitrogen levels and the associations between nitrogen and grain hardness have been reported by various studies (7,13,16,24). Other interesting observations were found when correlation analysis was performed between alcohol yields of 2009 versus 2010 for the wheat samples grown at either lower or higher nitrogen sites. Very strong correlation results were found for wheat grown at both locations. For wheat samples grown at the lower nitrogen site, a correlation result R = 0.8616 was found for 2009 versus 2010 alcohol yield; while a correlation result R = 0.8814 was obtained for wheat samples grown at the higher nitrogen site (Table 4). The difference between these correlation results is marginal and relates strongly to the discussion below. The slight difference in correlation results reported in Table 4 for PSY for both sites is reflected in the correlation results for residue viscosity (Table 4). They show that when higher correlation results were obtained for PSY, a lower correlation result was found for residue viscosity. The alcohol yield data complements the residue viscosity data because when more high molecular weight substrates are converted to alcohol during processing, there is a resultant reduction in residue viscosity and vice versa. Since similar strong correlation results were obtained for alcohol yields of wheat samples grown at the lower or higher nitrogen sites, storage period notwithstanding, these results show that although minor changes may occur regarding moisture and nitrogen of stored wheat over a period of storage time, long storage will not have a drastic effect on alcohol yield obtained from wheat.
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Table 5. Correlation between PSY versus TN for lower and higher nitrogen sites. Site
Year
R
Site 1 Lower nitrogen site
2009 2010 2009 2010
–0.2936 –0.5034 –0.3969 –0.7061
Site 2 Higher nitrogen site
Regarding the well-established relationship between grain nitrogen and alcohol yield, which is the main focus of this study, interesting results were obtained with regard to the type of relationship that exists between the two parameters when wheat was stored over a period of time. Following the first assessment of wheat after harvest in 2009, a very weak relationship (R = –0.2936) (Table 5) was found between total nitrogen versus alcohol yield for wheat grown at the lower nitrogen site (7). A 46% increase in this relationship (R = –0.5034) was, however, found between nitrogen and alcohol yield for the same wheat samples reassessed in 2010 (Table 5). Similarly, when the wheat samples grown at the higher nitrogen site were first assessed following harvest in 2009, although the relationship between alcohol yield and nitrogen was weak (R = –0.3969) (Table 5), it was stronger than that observed for wheat grown at the lower nitrogen site (Table 5). Again, a 44% increase corresponding to R = –0.7061 was found between nitrogen and alcohol yield for the same wheat samples grown at the higher nitrogen site and reassessed in 2010 (Table 5). In general, these results show that loss of moisture during storage of wheat improved the relationship between nitrogen content of wheat and alcohol yield of lower and higher nitrogen wheat to a similar degree (44–46%).
Conclusions This study has shown that the links which exist between some of the parameters used in assessing wheat quality, such as moisture content, grain total nitrogen, grain hardness, and alcohol yield, are more complex than originally thought. This complexity increases when grains are stored for a long period of time. The changes that occurred during the storage of wheat affected important relationships such as grain moisture content, nitrogen, and alcohol yield of wheat in different ways. Increases in alcohol yield were found when wheat samples grown at the lower nitrogen site were reassessed in 2010. This set of wheat samples had higher moisture levels at harvest, and also a higher loss of moisture during the one year storage period. In contrast, a decrease in alcohol yield occurred when the wheat samples grown at the higher nitrogen site were reassessed in 2010. This set of wheat samples had lower moisture levels at harvest and also lower losses of moisture during the storage period. Both wheat samples grown at either the lower or higher nitrogen site showed very slight increases in total nitrogen content. Although the increase or decrease observed for alcohol yield of stored wheat is difficult to explain, it is possible that this was caused by changes in the moisture content of stored wheat. Loss of moisture during wheat storage is likely to alter carbohydrate-protein binding patterns. This is also likely to affect the hydrogen bonding pattern as well as the additional energy input required to break hydrogen bonds during processing of wheat. This may help to explain why wheat samples grown at the lower nitrogen site, with greater losses of moisture during storage, produced higher alcohol yields. More studies will be required to confirm these observa-
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tions. The most interesting and important finding from this study, however, is that despite the changes with parameters such as moisture, total nitrogen, and hardness, no deleterious effect was found on the alcohol yield of stored wheat. This observation has important commercial value because it shows that when the wheat harvest is abundant, and surplus wheat is stored in a warehouse for a long period of time, there will be minimal deleterious effects in terms of alcohol yield obtained from such wheat when it is processed to produce alcohol. In this regard, users of wheat may purchase and stockpile wheat for a long period of time with no major concern regarding the quality of the stored wheat. ACKNOWLEDGMENT
The authors would like to thank Dr. Gordon Steele, Director of Research, Scotch Whisky Research Institute, for his permission to publish this work. REFERENCES 1. Agu, R. C. (2007). Some links between total nitrogen, β-glucan and steeliness in relation to barley and malt quality. Tech. Q. Master Brew. Assoc. Am. 44:32-39. 2. Agu, R. C. (2008). Some links between and amongst quality parameters used in assessment of barley adjuncts for food processing. Tech. Q. Master Brew. Assoc. Am. 45:274-278. 3. Agu, R. C., and Palmer, G. H. (1998). Some relationships between protein nitrogen and the production of amylolytic enzymes during malting. J. Inst. Brew. 104:273-276. 4. Agu, R. C., Bringhurst, T. A., Brosnan, J. M., and Jack, F. R. (2008a). Effect of process conditions on alcohol yield of wheat, maize and other cereals. J. Inst. Brew. 114:39-44. 5. Agu, R. C., Swanston, J. S., Bringhurst, T. A., Brosnan, J. M., Jack, F. R., and Smith, P. L. (2008b). The influence of nitrogen uptake on the quality of distilling wheat cultivars. In: Proc. 2nd Worldwide Distilled Spirits Conference, Edinburgh. J. H. Bryce, J. R. Piggott, and G. G. Stewart, eds. pp. 67-74. 6. Agu, R. C., Bringhurst, T. A., and Brosnan, J. M. (2006). Production of grain whisky and ethanol from wheat, maize and other cereals. J. Inst. Brew. 112:314-323. 7. Agu, R. C., Swanston, J. S., Walker, J. W., Pearson, S. Y., Bringhurst, T. A., Brosnan, J. M., and Jack, F. R. (2009). Predicting alcohol yield from UK soft winter wheat for grain distilling: combined influence of hardness and nitrogen measurement. J. Inst. Brew. 115:183-190. 8. Agu, R. C., and Palmer, G. H. (2003). Pattern of nitrogen distribution in barley grains grown in the field. J. Inst. Brew. 109:110-113. 9. Almond, A. (2005). Towards understanding the interaction between oligosaccharides and water molecules. Carbohydrate Res. 340:907-920. 10. Awole, K. D., Kettlewell, P. S., Hare, M. C., Agu, R. C., Brosnan, J. M., and Bringhurst, T. A. (2008). Prediction of alcohol yield from wheat grain, Aspects of Appl. Biol., Biomass and Energy Crops III. 90:161-164. 11. Barnes, P. J. (1989). Wheat in Milling and Baking. In: Cereal Science and Technology. G. H. Palmer, ed. Aberdeen University Press, Aberdeen, pp. 379-380. 12. Brosnan, J. M., Makari, S., Paterson, L., and Cochrane, M. P. (1999). What makes a good distilling wheat, In: Proceedings of the Fifth Aviemore Conference on Malting, Brewing and Distilling. I. Campbell, ed. Institute of Brewing, pp. 225-228. 13. Brown, G. L., Curtis, P. S., and Osborne, B. G. (1993). Factors affecting the measurement of hardness by near infrared reflectance spectroscopy of ground wheat. J. Near Infrared Spectrosc. 1:147-152. 14. Clarke, C., Woods, R. J., Gluska, J., Cooper, A., Nutley, M. A., and Brown, G. (2001). Involvement of water in carbohydrate-protein binding. J. Am. Chem. Soc. 123:12238-12247. 15. Davis-Knight, H., Weightman, R. M., Agu. R., Bringhurst, T., and Brosnan, J. (2010). Effects of fertilizer nitrogen and variety on the concentrations of non-starch polysaccharides in winter wheat for alcohol production. Aspects Appl. Biol. 101:155-162.
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