The Wine Press and the Cellar: A Manual for the Wine-Maker and the Cellar-Man

by Emmet H. Rixford

TESTING FOR SUGAR.

Any person, provided with one of the hydrometers mentioned, can easily ascertain the percentage of sugar contained in any must with tolerable accuracy, providing the grapes from which it is pressed are ripe; for if they are green, and contain an undue amount of acid, the density will be materially affected by that. There is no occasion, however, for making wine from green grapes in this State.

Fig. 2.

Hydrometer-Jar.

In addition to the hydrometer, it is necessary to be provided with a thermometer with which to ascertain the temperature of the must. Besides the hydrometer and the thermometer, the only other article necessary is a glass tube closed at the bottom and provided with a foot, so that it will stand upright, called the hydrometer-jar. ([Fig. 2].) This jar should have a diameter a little greater than that of the bulb of the hydrometer, and must be of such a height that the latter instrument will stand upright and float freely in it, when filled with a liquid. In the absence of the hydrometer-jar, an empty fruit jar, or a tall tin cup or can will answer its purpose. In performing the operation, see that all the articles used are perfectly clean, more particularly the hydrometer, for anything that would slightly affect its weight would render the result of the test useless. Having taken this precaution, press the juice from a small quantity of grapes and strain it through a cloth, and pour sufficient into the hydrometer-jar, that when the hydrometer is plunged into it, it will just bring the level of the liquid to the upper edge of the vessel, or to such a height that the figure on the stem can easily be read. Now place the thermometer in the must and ascertain its temperature, for the instruments are intended to be used at a certain degree of heat, although three or four degrees variation either way will not materially affect the result. Baumé’s instrument, as originally constructed, was graduated for a temperature of 10° Reamur, which corresponds with 54½° F.; but as constructed now-a-days, is generally graduated for a temperature of 58° or 60° F.; and Balling’s and Oechsle’s for a temperature of 63½° F. Some of Balling’s instruments sold in the market are graduated for 62° F. If it is found that the temperature is above or below the degree indicated, it may be lowered by cooling, or raised by warming, till about the right temperature is reached. Then the hydrometer, being clean, should be taken by the stem at the top and gradually lowered into the must until it floats. Press it down slightly with the finger and let it come to equilibrium, being careful that there is not a drop of water on the stem above the surface of the liquid, nor a bubble of air below. On looking at the stem where it meets the surface, it will be seen that the liquid there curves upwards around the instrument, and that the top of this curve marks one degree higher than the general surface. If the reading is taken from the point marked by the top of the curve (the figures reading downwards), add one degree, or in other words, ascertain the mark on the stem corresponding to the general surface of the liquid. If Balling’s scale is used, the number at this mark shows the percentage of sugar which the must contains; if Baumé’s is used, consult Table II or III, and opposite this number will be found the corresponding per cent. of sugar. If Oechsle’s scale is used, find from Table I or II the specific gravity and the corresponding sugar per cent. Under Table I instructions will be found for reading Oechsle’s scale. If Baumé’s instrument is used, and a table is not at hand, multiply the observed figure by 1.8, and the product will be nearly the per cent. of sugar.

Correction for Temperature.—It is known that a sugar solution or a must expands as the temperature increases, and contracts as it diminishes; and nice experiments have been performed to show the amount of dilatation and contraction at different temperatures, and the consequent variation in the specific gravity of the liquid, but there is considerable difference in the results of the researches of different authors, and it would seem that further experiments are necessary; but a rule may be deduced which may be used instead of changing the temperature of the must to make it correspond with that for which the instrument is graduated, and although not strictly correct, is sufficient for our purpose; and that is to add one-half per cent. to the sugar per cent. indicated by the hydrometer for every 15° F. above the standard temperature, and subtract ½ per cent. for every 15° below. For instance, if Baumé’s instrument shows 22½ per cent. of sugar at 75° F., the actual strength is 23 per cent., and it would mark that at 60°. If the same instrument shows 23½ per cent. at 45° F., the real strength is 23 per cent. In using Balling’s scale graduated at 63½° F., the 15° in our example would make 78½° for the first supposed case, and 48½° for the second.

In most cases the variation in temperature will be so little that it may be disregarded; but if the test is made soon after the grapes have been exposed to a hot sun, the must may show a temperature of 90° or 95° F., and it would indicate one per cent. less than its real sugar strength. But the temperature would go below the freezing point of water before the must would mark one per cent. too much.

As the must contains a small quantity of acids and extractive matter which affect its density, some authors recommend that from one-tenth to one-fifteenth of the figures indicating the density by Baumé should be deducted, calling the remainder sugar, and this is about equivalent to deducting one for every twelve per cent. of sugar. But if the grapes are ripe and the must is strained, for all practical purposes all of the solid matter may be called sugar, considering that we make a pretty liberal allowance of sugar for one per cent. of alcohol. Fresh must should always be taken for the purpose of testing for sugar, for as alcohol is much lighter than water, if fermentation has commenced, it will be impossible to ascertain the amount of sugar by means of the hydrometer.

Sugar and Alcohol.—It will be shown in the chapter on fermentation that, in actual practice, it takes about two per cent. of sugar, as indicated by the hydrometer, to produce one per cent. by volume of alcohol; therefore, divide the percentage of sugar contained in the must, as shown by the hydrometer, by two, and the quotient is approximately the per cent. of alcohol which will be contained in the wine after complete fermentation.