- Sake metre value (SMV)
A unit established to express the specific gravity of sake. It is calculated by the following formula: SMV = (1÷specific gravity – 1) x 1443. (Specific gravity may also be measured in units Baumé. One unit Baumé is equivalent to ten on the SMV scale. For example, a sample of sake (or moromi) of Baumé 3.0 has a SMV of -30, and one of 2.0 has an SMV of -20. In the early stages of moromi fermentation, readings are given in Baumé (Japanese bo-me, ボーメ); from Baumé 3.0 (SMV -30) onwards, and in the case of analysis of conventional sake, readings are usually given as SMV.)
SMV is measured by floating a sake meter (hydrometer) in the sample of sake at 15°C. Where the weight at 15°C is the same as for pure water at 4°C (a specific gravity of one), this is read as (±) zero on the SMV. Lighter samples give a plus reading, and heavier ones give a SMV in the minus range. Accordingly, pure water measured at 15°C gives an SMV reading, not of (±) zero, but (+)1.26
The sweetness of sake comes from sugar, and the higher the sugar content, the higher the specific gravity, so the SMV reads higher in the minus range. On the other hand, dryness comes from alcohol, so sake with a higher level of alcohol tends to the plus side of the SMV range. Thus sweet sake inclines to the minus range, and dry to the plus range, so the SMV is used as a general indicator of dry- and sweetness in sake. However, sweet and dry are sensory perceptions, where SMV is simply a reflection of specific gravity, so the two do not always appear to correlate. The sugar glucose is sweet, but, the more other sugars influence the SMV, the less sweetness will be apparent. Further, the sense of sweet or dry is affected by the level of acidity. The higher the acidity, the drier the sake will taste. Sake with low acidity tends to taste sweeter.
The average SMV range is from 0 -＋5. Sake sweeter than the zero mark (that is to say in the minus range) is considered ama-kuchi ; that which reads more than +5 may be said to be kara-kuchi. According to the Tax Agency’s market survey of sake products in 2012, the average values for various types of sake were: futsu-shu +3.7; ginjo-shu +4.3; junmai-shu +4.