When I make wine, I want the sugar content of the must prior to fermentation to be at or very near 24% sugar. Once the juice is collected, the easiest way to measure sugar content is to use a refractometer (also known as a Brix Refractometer) that is designed for the purpose and has a range of 0 to 32% Brix (in other words 0 to 32% by weight of sugar in a solution). This instrument can be purchased at a wine supply shop or on line. These days they are not as expensive as they once were, and for measuring sugar they are convenient, easy to use, and come in at least two types. In one type the instrument's readings are self correcting for temperature and in the other type they are not but need to be corrected by the user if the temperature of the must at which the reading is obtained differs from the temperature for which the instrument is calibrated. The one that I use is calibrated for 20oC (68oF); therefore, I need to correct the readings I get if the temperature differs from this value, but that is easy to do.
I take a sample of the freshly pressed grape juice, and using the refractometer and a thermometer I record the percent sugar in the must and its temperature. (A good quality refractometer from a reputable supplier like Fisher Scientific comes with excellent instructions for its use.) As an example, the Muscat grape juice that I talked about in the previous blog gave a reading of 23.2% at 28oC. At this temperature a correction of 0.62% to 0.63% needs to be added to the reading giving 23.8% sugar in the must. For me this is close enough to 24%, and no sugar addition is needed.
Things are a little different when the sugar content of a grape juice is above 24% as was the case for this year's (2013) rose' made from Merlot grapes. When I measured the sugar content of the rose' must I got a corrected value of 25.6% at 27oC. This is too high and would result in high alcoholic wine if allowed to ferment to dryness. An easy remedy is to add to the must tap or spring water never distilled water; but how much to add? To answer this question requires a little work, but not much.
An approximate method for figuring out how much water to add is to do this simple arithmetic:
In the case of my rose' must here are the results:
So here's what I did, I added 4 liters of water to the 55 liters of original must. After a thorough mixing as a check I took a sample, measured its percent sugar and its temperature. The uncorrected percent sugar was 23.6 at 27oC and 24.1% when corrected for the temperature. This is close enough to the target of 24%. Notice that this method is approximate and underestimates the amount of water to use, so if I don't quite make the percent sugar I want I can add a little more water. Incidentally, this method works for gallons as well as liters, too. I just substitute gallons for liters in the calculation.
That's all well and good, but what happens when a grape juice has a lower reading from 24% for sugar; what do I do? Actually that's what happened with this year's (2013) Estate Rose' must. I got a corrected 22.9% sugar in the 35 liters of must. To say that a juice has a 22.9% sugar content is to say that for every kilogram of juice there is 0.229 kilogram of sugar in it (or for every pound of juice there is 0.229 pound of sugar in it). But I want a juice that is 24% or 0.24 kilogram of sugar per kilogram of juice. Here is what I do to make the correction:
In the case of my Estate Rose', here are the results:
After adding 385 grams of sugar to a portion of warmed must and stirring it until it completely dissolved, I added it to the remaining juice and mixed it in well. The corrected refractometer reading for this must after the addition of the sugar gave 23.7%, close enough to the 24% that I want. Once again this method underestimates the amount of sugar to add, and that is a good thing. Once the sugar is there, I have to live with it.
When I am measuring volume in gallons (US) and weight in ounces I multiply the result of 2. above by the total volume in gallons and the factor 0.1335. So, in my case since 35 liters is the equivalent of 9 and a quarter gallons (9.25 gallons), the calculation becomes 11 x 9.25 x 0.1335 = 13.6 ounces of sugar to add to the must.
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I take a sample of the freshly pressed grape juice, and using the refractometer and a thermometer I record the percent sugar in the must and its temperature. (A good quality refractometer from a reputable supplier like Fisher Scientific comes with excellent instructions for its use.) As an example, the Muscat grape juice that I talked about in the previous blog gave a reading of 23.2% at 28oC. At this temperature a correction of 0.62% to 0.63% needs to be added to the reading giving 23.8% sugar in the must. For me this is close enough to 24%, and no sugar addition is needed.
Things are a little different when the sugar content of a grape juice is above 24% as was the case for this year's (2013) rose' made from Merlot grapes. When I measured the sugar content of the rose' must I got a corrected value of 25.6% at 27oC. This is too high and would result in high alcoholic wine if allowed to ferment to dryness. An easy remedy is to add to the must tap or spring water never distilled water; but how much to add? To answer this question requires a little work, but not much.
An approximate method for figuring out how much water to add is to do this simple arithmetic:
- divide the % sugar in the juice by the % sugar that I want,
- multiply the result in 1. by the total volume of must,
- the result of 2. is the new total volume of must after the addition of water,
- subtract from 3. the original volume of must that I had,
- and the result of 4. is the volume of water to add.
In the case of my rose' must here are the results:
- 25.6/24 = 1.067,
- 1.067 x 55 = 58.7 liters which is almost 59 liters,
- 59 liters,
- 59 - 55 = 4 liters,
- and 4 liters of water must be added to the 55 liters of must.
So here's what I did, I added 4 liters of water to the 55 liters of original must. After a thorough mixing as a check I took a sample, measured its percent sugar and its temperature. The uncorrected percent sugar was 23.6 at 27oC and 24.1% when corrected for the temperature. This is close enough to the target of 24%. Notice that this method is approximate and underestimates the amount of water to use, so if I don't quite make the percent sugar I want I can add a little more water. Incidentally, this method works for gallons as well as liters, too. I just substitute gallons for liters in the calculation.
That's all well and good, but what happens when a grape juice has a lower reading from 24% for sugar; what do I do? Actually that's what happened with this year's (2013) Estate Rose' must. I got a corrected 22.9% sugar in the 35 liters of must. To say that a juice has a 22.9% sugar content is to say that for every kilogram of juice there is 0.229 kilogram of sugar in it (or for every pound of juice there is 0.229 pound of sugar in it). But I want a juice that is 24% or 0.24 kilogram of sugar per kilogram of juice. Here is what I do to make the correction:
- I subtract from my target percent the percent that I have,
- multiply the result of 1. by 10,
- and multiply the result of 2. by the total volume of must in liters.
In the case of my Estate Rose', here are the results:
- 24.0 - 22.9 = 1.1,
- 1.1 x 10 = 11,
- and 11 x 35 = 385 grams of sugar to add to the must.
After adding 385 grams of sugar to a portion of warmed must and stirring it until it completely dissolved, I added it to the remaining juice and mixed it in well. The corrected refractometer reading for this must after the addition of the sugar gave 23.7%, close enough to the 24% that I want. Once again this method underestimates the amount of sugar to add, and that is a good thing. Once the sugar is there, I have to live with it.
When I am measuring volume in gallons (US) and weight in ounces I multiply the result of 2. above by the total volume in gallons and the factor 0.1335. So, in my case since 35 liters is the equivalent of 9 and a quarter gallons (9.25 gallons), the calculation becomes 11 x 9.25 x 0.1335 = 13.6 ounces of sugar to add to the must.
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