Hii Birrofilo,
I would like to ask if rice wine liquid can be measured with the same device that measure wine "specific gravity" ?
From what i understand, Specific gravity measurement system for wine has being in the sense - "calibrated" over the time, to measure the content of sugar in grape mash. A certain SG in the grape juice means a certain amount of sugar in the juice...(so can decide need to add in sugar by how much to do initial fermentation to achieve a desired ABV outcome.
But since rice fermentation liquid is of different liquid density than of grape juice and sugar mash..
Using the same SG system (as of grape wine)..does the SG shows the corrent amount of sugar of the rice fermenting liquid ?
Eg: maybe plain non-sweeten rice liquid itself is different than non-sweeten grape juice... in this case, how can one use SG properly for rice wine ?
Specific gravity, or relative density, is simply a measurement of the mass of a certain volume of matter in comparison to the mass of the certain volume of another matter which you assume as the comparison unit, which is normally water.
When we say that a certain liquid has a specific gravity of 1,040 we only mean that, if the mass of a certain volume of water is 1, the mass of the same volume of the liquid is 1,040. This can also be expressed as saying that the liquid has "40 points" of specific gravity.
Those 40 points are composed of a mass which is not water. It can be sugars, or starches, or proteins, or maybe fats, or a little bit of any of those.
In the case of wine, the sugars present in the wine are entirely fermentable: they will all be digested by the yeast, in normal conditions, i.e. all converted into CO2 and various alcohols, which will result in a wine which is dry.
In the case of beer, the sugars present in the wort are not entirely fermentable: some of them will be converted into CO2 and alcohols, and some others, more complex, will not be converted and remain in your beer as "body", "maltosity".
That means that a certain gravity, such as 1,040, has a different "meaning" for different worts, because in wort A this can be composed of mostly fermentable sugars (which will give after fermentation a beer with more alcohol and less body) and wort B can be composed with a higher percentage of non fermentable sugars (which will give after fermentation a beer which has less alcohol and more "body" than wort A). The homebrewer controls the fermentability of the wort in the mashing phase (and, see below, by selecting a certain yeast).
Also, yeasts have different opinions regarding what they see as "food". Some yeast strains will digest more than others, so the same wort can end up with a lower final density with a more "voracious" yeast, and with a higher final density with a "less voracious" yeast. In the first case, the "attenuation" is higher than in the second case.
If you steep rice in water you get mostly starches, which are not considered food by any yeast. You must first convert the starches into sugars (simple sugars, more complex sugars, that depends of the mix of enzymes, the temperature etc.) and then give those sugars to your yeast, and depending on the yeast and the sugar, you will end up with a certain "attenuation" and a certain residual density.
For wine and sake you want normally to end up with total real attenuation, no sugars left. For beer, you don't want that, you always want some "maltosity", some residual density, unless you are preparing a beer for distillation.
The instrument you use is the same and the meaning, the density, is the same.
If you want sweet wine, you must have more sugar in your wort than your yeast can digest (or you must stop fermentation before the yeast has eaten all the sugars). Yeast normally get drunk and go to sleep when the alcohol content reaches a certain threshold, which is different from strain to strain. Wine yeasts have a higher alcohol tolerance than beer yeast in general.