Start of the New Wine Season and Making Red Wine

Sample of Estate Grapes

For this year, 2012, August 26^th marks the beginning of my new wine year.  So, on this day I picked my grapes which are a mixture of Merlot and Cabernet Sauvignon which will produce this year's Estate Wine.  I got a total of four bushel size containers of grapes.  I promptly crushed them, removed their stems, and placed them in a 75 liter plastic barrel that serves as the primary fermentation vessel.




Packets of Dry Wine Yeasts

Once in the primary fermenter I did a sugar analysis of the grape juice and removed about one quart of the must which I boiled, let cool to room temperature, and added one 5 gram packet of dry Pasteur Red yeast, a wine yeast.  This mixture of wine yeast and boiled, cooled must is called a yeast starter.  After about 12 to 14 hours, this starter was foaming with the yeasts actively converting sugar in the must into carbon dioxide gas (hence the foaming) and alcohol.  I poured the yeast starter into the primary fermenter, thus inoculating the must with the Pasteur Red.

Boiling Must to Which one Packet of Pasteur Red
Will be Added When Cool

I can not afford to let too much time pass once the grapes are crushed before I inoculate the must.  In my case, there are three reasons for this.  The outside skins of the grapes are covered with wild yeasts and I don't want these wild yeasts to have much of an influence on the quality of the wine produced.  The temperatures that I work at in this warm climate are high, usually above 25^oC, and at these temperatures yeasts are very active.  Finally, I do not use sulfites in my wines; sulfites are added to musts to destroy wild yeasts and other microbes.  Over the years, I have found that if no more 10 to 24 hours pass before inoculation of the must, wild yeast activity is low and insufficient to compete with commercial wine yeasts that I use.




A Refractometer

Using a refractometer I did a sugar analysis of the must along with three water dilutions of the must.  A refractometer measures the sugar content of grape juices.  It is easy to use, but the largest source of error using the instrument is incurred when the temperature of the measurement is not also recorded.  As it turned out, all of the readings using the refractometer occurred at a temperature of 28^oC, and I found the sugar content to be 23.6% by weight, which gives a potential alcohol content of about 13.4% by volume.  I will say more about using a refractometer in a later blog.

Mixing the Must in a Primary Fermenter

Once the must is in the primary fermenter and inoculated with yeast, it is necessary to mix the must well at least one time each day.  Primary fermentation is active for about 7 to 10 days.  After that length of time it slows considerably as shown by the lack of foaming upon stirring, and it is at this time that the must must be transferred to the secondary fermentation containers. 

Measuring the Alcohol Content of Wine

Each year I try to make four different wines produced from locally grown gapes: a white made from Muscat grapes, a rose' made from Merlot grapes, a Merlot, and an estate wine made from a mixture of Merlot and Cabernet Sauvignon grapes.  This is the time of the year that I bottle my wines, but before I do I measure their alcohol content for no other reason than when people ask me how strong is the wine, I can give them the answer.


There is more than one method used to measure the alcohol content of wine.  Some require expensive equipment and detailed procedures, and others require no more than a hydrometer, an instrument that all serious home wine makers have as standard equipment.  The hydrometer (there are different kinds of these and they come in different ranges) is used to measure the specific gravity of water solutions.  Two important water solutions in wine making are sugar in water and alcohol in water.


Technically, and in the limited sense that it applies to wine making, specific gravity is the ratio of the mass of a volume of solution of sugar in water (must) [or alcohol in water (wine)] to the mass of an equal volume of water measured at a specific temperature.  The specific gravity is then related to the exact composition of the solution, that is, the percent of sugar in the must or the percent of alcohol in the wine.  So, as an example, at 20^oC the specific gravity of a 20% solution of sugar in water is 1.083 while that of a 24% solution is 1.101;  thus, if you measure and find that the specific gravity of a must is 1.083 at 20^oC you may assume that it contains 20% sugar.

Two Hydrometers

The hydrometer is a long cylindrical glass instrument which has enclosed within the glass housing a visible scale or scales.  The longer one of the two shown actually has three such scales:  one for measuring specific gravity, one for measuring percent sugar by weight, and one for measuring potential alcohol by volume.  The other, shorter hydrometer is a Gay Lussac and measures the percent by volume of alcohol directly.  Each hydrometer is designed to give direct  readings at a particular temperature.  The longer one is intended for use at 60^oF and the Gay Lussac at 68^oF.  Hardly ever are these exact temperature conditions reached in actual practice.


To measure the amount of alcohol in my wines, I have used three methods.  The simplest of these is to measure the specific gravity and temperature of the must just prior to the start of fermentation, and then after almost one year later to measure the specific gravity and temperature of the resulting wine.  The two specific gravity measures are converted into what is called potential alcohol, and the difference between the before fermentation potential alcohol reading minus the wine's potential alcohol reading gives the alcohol content of the wine.  The temperature is recorded because specific gravity depends on temperature.  In other words, the specific gravity of a solution at 60^oF will not be the same value that it would be for that solution at 80^oF.  Specific gravity tables are published to apply at certain standard temperatures, such as 60^oF (15.56^oC) or 68^oF (20^oC) as well as others, and in order to use these tables accurately most specific gravity measurements must be corrected for temperature.


Consider this example, on September 7, 2011, I measured the specific gravity of my white must just before the start of fermentation and found it to be 1.102 at 78^oF (25.6^oC).  Then, on July 1, 2012, I measured the specific gravity of the resulting white wine to be 0.992 at 77.4^oF (25.2^oC).  Both of these measurements were obtained using the 60^oF hydrometer, and both specific gravity measurements must be corrected for temperature.  At around 77^oF to 78^oF the use of a 60^oF hydrometer calls for a correction of 0.002 to be added to each specific gravity;  thus, we get 1.104 and 0.994, respectively, for the corrected specific gravities.  With these corrected specific gravities, the potential alcohol table that comes with the hydrometer gives for the first reading 13.7% and for the second 0%.  The difference between these two readings is 13.7% alcohol by volume, so my white Muscat wine is 13.7% alcohol by volume.

Distillation of Rose' Wine

Earlier I said that I determine the alcohol content of my wines by different methods.  The potential alcohol is one method that I use, but I also use a weight method and a distillation method, too.  By these two latter methods, the alcohol content of my white Muscat wine is 14.1% and 12.7%, respectively.  I present these results as an illustration of the fact that the methods available to the home wine maker for alcohol determination are approximate, and, by far, the potential alcohol method is the easiest and least expensive method to use, and it gives very acceptable results.

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