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April 10th, 2011 at 9:58 am

Rice Malt, Not for Sake but still interesting

While researching rice and enzymes I came across an article on how steep time and temperature influence rice malt enzyme production. Malting is a major part of most beer brewing but while sake is, by some definitions, a beer, it does not use malt; not rice malt, not any kind of malt. Instead the rice used for sake is milled to remove the outer layers of the grain, which destroys all possibility of malting.

Malting is the process of transforming a grain from a seed to a malt that contains not only the starches and proteins that where present in the seed but also enzymes that can be used to convert the starches and proteins in the malt to sugars and amino acids.

To malt seed, the seed is steeped in water and allowed to dry a little in order to awaken the seed to begin to grow. The steeping and drying may be carried out several times to fully engage the embryo’s growth but ensure the seed does not drown. Once the embryo has begun to sprout roots and a shoot, a maltster will halt the embryo’s transformation by heating or kilning the grain. This prevents the enzymes from fully distributing throughout the endosperm and converting it before it is ready to be used.

In “The Influences of Steeping Duration and Temperature on the α- and β-Amylase Activities of Six Thai Rice Malt Cultivars (Oryza sativa L. Indica)” by Neung Teaumroong, Et. Al., the authors look at how steeping time and temperature interact to produce more effective malting of rice. They note that rice, in contrast to most grains, can be germinated in anaerobic conditions. For this reason a single steeping can be used to induce germination, there is no worries about drowning the seed.

This study looks only at Indica rice which makes me wonder about the differences that might exist for Japanica or Javanica but we get what we get. Interestingly, while dealing only with Indica, both glutinous and non-glutinous rice cultivars are included. We, I, often thing of equating the categories of glutinous with Japanica and non-glutinous with Indica, however, as is demonstrated by the cultivars chosen for this study each major group contains cultivars with varying amounts of amylose. It is the amount of amylose in the rice that determines the degree to which it would be considered glutinous or non-glutinous.

The study finds that rice moisture increased rapidly during the first 24 hour period of steeping and then much more gradually for the next two 24 hour periods. Also, that moisture content is increased slightly by steeping at higher temperatures. While these findings are for all six cultivars the exact amount of moisture uptake was cultivar dependent.

While the moisture content does not exceed 35% for most cultivars even after 72 hours of steeping, this is enough for rice germination. In contrast, Barley germination requires around 45%.

Moisture uptake rate for steeping

Moisture uptake rate for steeping

Moreover, the study finds that α-amylase continues to increase until the end of germination; that is through all 6 days of germination. However, β-amylase rises faster but then begins to decline on the 4th or 5th day depending on cultivar. As it turns out the maximization of β-amylase also maximizes the potential for reducing sugar. In all cases this maximum was found with a short steeping time, 24 hours, at 30°C but varying the number of germination days from 4 to 5 depending on the cultivar.

In this analysis the authors have determined the most efficient means by which to malt rice. Using there guidelines may improve the malt output to the extent that imports of other types of malt could be reduced.

I found this study to be very interesting both for its connection to beer production through the use of malts and for what it tells us about rice, the main ingredient of sake.



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