Determining the weight of the must.
One could also speak of determining the sugar content of the juice, but the wording "must weight" indicates the method of measurement; the must actually weighs.
Before I deal with the analysis, which you can make on your own, a few basic considerations first. The juice that is standing in front of us in a transparent vessel folds up – depending on the type of fruit, from which it was created – w 80 – 90, and even 95% from water.
The rest is sugar, sugar-free extract, tannins, pect, protein, aromatic ingredients, mineral and dyes. Their composition varies depending on the year, places of cultivation, climate, the degree of fruit maturity and the method of their processing. Apart from sugar, acids are the most important components of the general extract, the quantity of which varies depending on the type of fruit. The sugar content in grapes is on average just under 20%, and acids on average 1%, apples also contain approx 1% acids, but their sugar content is average 7%. The fruit richest in acids is the lingonberry, which contains more than 2%, and is merely in it 1,5% sugar. However, there is only pears 0,3% acids, a ponad 8% sugar.
They are Values, which must be taken into account when making wine, but only one ingredient in the juice, occurring in the smallest amounts, the so-called sugar-free extract, creates it, which is later referred to in the finished wine as a "bouquet". It cannot be analyzed at home, however, it can be determined by taste and smell.
When analyzing a juice, next to the water content, we will be most interested in the sugar content, because it plays a major role in the fermentation process. Although there are different types of sugars in fruit juice, however, the overall sugar value should be calculated, which is measured as follows.
A measuring instrument is used for this, which was invented by the pharmacist Ochsle in the last century. It is easy to use, it is easy to read the measurement results, and it works according to the following principle.
The weight of one liter of water, 1000 grams, is considered a constant value. By weighing the grape juice, Mr. Ochsle said, that its weight increased with the year of birth, the degree of fruit maturity, place of cultivation and climate and was on average 1060-1080 grams. Hence Ochsle made the conclusion, that excess weight, and so 60-80 gram per liter, must be the weight of the extract (mainly sugar). The scale for weighing the must that he constructed indicates this excess weight.
The measuring instrument is a glass container loaded with lead or mercury and terminated at the top with a cylindrical glass tube with a scale. The lower the specific gravity of the liquid, the lower the container sinks. After immersing the scales for weighing the must in a liquid with a specific gravity, the excess weight is read on the scale. "Ochsle graduation" covers the range from 0 do 130 grams (see the drawing above).
If, therefore, excess weight 1 liter of juice in relation to the weight of water 1000 g is 55 g, is the weight to the must, also known as the areo-metro, with a densimeter or a sugar meter, descends to the level "55".
Get a beaker with a capacity for measurements 250 cm3. It is filled with juice, and then the sugar meter is dipped into it. It should flow freely in the juice, without touching the sides or bottom of the beaker. Only then can the juice weight be accurately read, if the liquid has been previously filtered and does not contain fine fruit particles (pips, earwig, pulp, etc.). You should also pay attention to this, to remove any air bubbles from the juice. The weight of the must can only be determined from the fresh juice, because in juice, where fermentation started, the sugar has already been transformed.
To get an accurate measurement, both beaker, as well as the sugar meter must be clean and degreased, otherwise, the results will be falsified. Therefore, they should be thoroughly washed after each use.
The exact measured value can only be read a few minutes after the measuring tool has been immersed in the liquid, because its temperature should be close to that of the juice. The weight of the must is read by the liquid either from below or above. Read the instructions for use of the hydrometer carefully.
In addition, one more thing should be considered. Each sugar meter is marked for a temperature of 20 ° C, it means, that only then indicates the correct value, when the juice is at exactly this temperature. If the measurement is made at a different temperature – and this is the case most often – you have to make a correction to get the results.
Dane, for correcting the results, are located in the lower part of the sugar meter, ended with a bubble, on the left side of the thermometer (therefore you should always buy a sugar meter with a thermometer!). Depending on the temperature, it adds up (at higher temperature) or subtracts (at lower) the appropriate correction value.
The read and, if necessary, corrected value of the must weight should be written down in a book with notes on the maintenance of the cellar or marked on the fermentation vessel.
