Effect of Different Steeping Conditions on Endosperm Modification and Quality of Distilling Malt

Abstract

J. Inst. Brew. 116(2), 125-133, 2010This study showed that when barley was steeped in water for either 8 h or 16 h, hydration of endosperm materials was suboptimal and modification of endosperm materials of barley malt was inadequate. The malt produced under these steeping regimes gave poor friability scores and produced a large number of whole grains. When barley was steeped for 24 h on a continuous basis, or when a regimented standard steeping method was used, the malt produced gave higher friability scores and a much lower number of whole grains. An important relationship was found between friability scores and whole grain results for the malt samples produced under these conditions. Optic barley, whose endosperm was more difficult to hydrate, gave a strong negative correlation between friability scores and number of whole grains at R 2 = 0.8689. Oxbridge, whose endosperm was more easily hydrated, gave a much stronger negative correlation between friability scores and number of whole grains at R 2 = 0.9769. Rapid visco-analysis (RVA) results also confirmed that steeping the barley samples for only 8 h or 16 h produced malt that modified poorly as the RVA peak viscosities were very high. RVA pasting results further confirmed that when barley was steeped for 24 h on a continuous basis, or when a standard regimented steeping method was used, good quality malt was produced and no differences were found in the RVA peak viscosities of the barley malt samples produced under the two different steeping conditions. The results of protein breakdown (proteolysis) during these experiments, measured in terms of total soluble nitrogen (TSN) production, or soluble nitrogen ratio (SNR) further confirmed that optimal proteolysis was achieved when barley was steeped for either 24 h on a continuous basis, or with a standard steep. Optimal results were also found for hot water extractable materials such as hot water extract (HWE) and free amino nitrogen (FAN) when barley was steeped for 24 h or the standard steep. The 24 h continuous steep for barley produced quality malt comparable to that obtained when the standard regimented steep was used for steeping barley. For both Optic and Oxbridge barley, with a 24 h continuous steep, produced malt that gave significantly higher fermentabilities and PSY values, regardless of germination time, than those obtained using a standard regimented steep. Therefore steeping barley for 24 h on a continuous basis prior to malting will produce good quality malt for some barley samples/varieties. This will help to reduce water usage during steeping, will save steeping time thereby reducing malting time and will reduce the amount of water for effluent treatment. All of these factors result in an overall cost saving for the malting industry.

In situ study of water uptake by the seeds, endosperm and husk of barley using infrared spectroscopy

“…As previously reported, different varieties tend to have different water uptake rates. The observed differences in the water uptake might be related with the inherent physical and biochemical characteristics of the endosperm such as proteins, starch, cell wall components, starch granule characteristics, and endosperm structure [1,3,4,7,9]. According to several authors, hydrogen bonding in water-based solutions can be influenced not only by temperature, but also by solutes [12,31].…”

“…Detailed knowledge of water uptake by the barley kernels is of importance not only to better understand seed germination but also to determine the biochemical changes in the grain that have an effect on quality as well as to optimize industrial processes [1,3,4,7,9]. The physical characteristics of the barley endosperm can have a significant impact on the processing behavior of barley, where its compactness (structure of the endosperm is referred to as steeliness and mealiness) has been regarded as a useful indicator of malting quality in barley [1,3,4,7,9]. It has been reported that during the Table 1 Cross validation statistics for the prediction of water uptake in single whole seeds.…”

“…Variations in both the amount and rate of water uptake by the seed might lead to inefficient hydration and therefore to over or under modification of the endosperm for industrial uses (e.g., malting) [1,3,4,7,9].…”

“…The uptake of water by barley seeds is an essential and initial step towards germination [1,3,4,7,9]. This step is of importance not only for the direct effect on crop germination but also from a technological point of view (e.g., in the malting process it is often referred to as steeping) [4,7,9] Abbreviations: ATR, attenuated total reflectance; MIR, mid infrared; NMR, nuclear magnetic resonance; NIR, near infrared; PC, principal component; PCA, principal component analysis; PLS, partial least squares; PRESS, prediction residual error sum of squares; R 2 , coefficient of determination in cross validation; RPD, residual predictive deviation; RWU, rate of water uptake; SD, standard deviation; SECV, standard error of cross validation.…”

The influence of starch pasting properties and grain protein content on water uptake in barley

“…peak viscosity) are associated with amylose, amylopectin and starch content, biophysical characteristics of the endosperm (e.g. granules) as well as a tendency to produce malts with better modification . Bryce and collaborators also reported that high PV can be associated with starch being incompletely hydrolysed.…”