The David J. Schryver Winemaking Computations Primer

As previously mentioned, I found myself searching all over to get advice on making certain computations needed in the winemaking process.  This page is a brief look at that.
Adding sugar to the must if your starting sugar level (Brix) is too low
Background:

Most winemakers agree that you should start the grape winemaking process with a must of between 18o and 21o Brix.  The degrees of Brix is basically the percentage of sugar by volume of your must or juice.  For example, 20o Brix means that 20% of the volume of your juice is sugar.  Some people rightfully believe that if you like a drier wine, you should start on the lower end of that range.  If your tastes are sweeter, start on the higher end.  After fermenting your wine, if it is too dry, you can always add sugar, after treating with Potassium Sorbate to inhibit the yeast.  If it is too sweet, however, the only way to reduce the sweetness is to water it down, which also reduces the alcohol level, the acidity and the body.

For this computation, we need to know some numbers.  You need to know the Desired Brix, which I will call the DB.  That is the number, probably between 18 and 21 that we discussed in the previous paragraph.  You also need to know the Starting Brix, or SB.  This can be found by using a refractometer or hydrometer or will be provided by the business where you bought your supplies.  If you measure your Starting Brix, remember to stir the must well. Simply dipping into the juice and extracting a drop or two will probably result in a lower than accurate reading because the majority of the sugar is lower in the juice.  This could cause you to add more sugar than desired.

If your SB is equal to or more than your DB, you are home free.  You don't need to add sugar.  That usually isn't the case.  You will also need the size of your batch ... 3 gallons, 5 gallons, whatever!  If you have a partial gallon amount, a reasonable estimate will work.  For example if you have about a quart over a 5 gallon carboy, call it 5-1/4, or 5.25

We will also note that .125 pounds of sugar (1/8 pound) will raise 1 gallon 1 Brix or degree.   One ounce is .0625 pounds.  When I originally researched this, I found that most sites use the conversion of 1 pound of common table sugar is about 2.25 (2-1/4) cups.  I used this for several years.  At some point, I used this conversion when I needed 2.7 pounds and realized I was going to come up short with a 3-pound bag.  I ran an experiment with a 4-pound bag from a different manufacturer with the same results.  I now use the conversion of 1 pound = 2 cups and it is more accurate.  You can also use corn sugar or honey, but those values are different.  The information in this paragraph is basically a set of facts which you don't really have to worry about.

Calculate: Get your calculator and follow these steps ...
  1. DB - SB ... in other words, subtract your Starting Brix from your Desired Brix ... this will give you the number of degrees of Brix you need to raise your must.
  2. Multiply this value by the number of gallons of your must.
  3. Now divide this by 8 ... this gives you the number of pounds of sugar you need
  4. Multiply this value by 2 and you have the number of cups of table sugar you need to add to your must or juice.

Obviously, if you need more than the amount in the bags you are using, save yourself some time.  Use a whole bag and only convert the balance.

Treating with Calcium Carbonate to lower TA
Background: The TA (total acidity) of your must or juice should be between 0.70 and 0.85%.  If it is higher than this, you will probably want to treat it to lower it.  In my research, I found several points that are important.  First of all, the TA of a must will drop about 0.12% in the normal fermentation process.  Secondly, if you also cold stabilize, which is highly recommended in higher acid situations, the TA will drop about 0.2%.  Having said that, my personal preference is to have the 0.70 to 0.85% range without these other considerations.

The first time I treated with Calcium Carbonate, my package had no instructions.  I researched on-line and found that  2.5 grams of Calcium Carbonate will reduce1 gallon of must by 0.1% TA. Since we live in the USA, 2.5 grams probably doesn't mean much to most of us.  Some basic math converted this to about 1 teaspoon.

The second package of Calcium Carbonate I bought had instructions on the bag.  It stated "1/2 teaspoon of Calcium Carbonate will reduce 1 gallon of must by 0 .1% TA".  Because of this disagreement, I went on-line to see what I could find.  One website agreed with this 1 teaspoon figure.  Another said that 1 tsp = 2.1 grams, which implies the figure is slightly less than 1 teaspoon.  I also consulted with two friends with considerably more winemaking experience and expertise than I have.  They agreed with the 1 teaspoon number.  Bottom line, follow the instructions on the package.  If there aren't any, go with the 1 teaspoon per gallon per .1% figure.

There are some other points we need to consider.  First of all, treating with Calcium Carbonate will raise the pH of your must.  For each 0.1% you drop your TA, you will raise your pH by 0.1.  Since you shouldn't elevate your pH to over 3.5, that can also become an issue.  For example, if your starting TA is 1.05 and your pH is 3.2, lowering your TA to 0.85% will raise your pH to 3.4 which is perfectly fine.  However, if your starting TA is 1.05 and your pH is 3.4, lowering your TA to 0.85% will raise your pH to 3.6 which is too high.  In this case, you might want to add sugar water or combine these two techniques.  One last note ... it is generally recommended that you not attempt to use Calcium Carbonate to drop the TA by more than 0.3%.

Calculate: This one is quite easy.  For each unit of Calcium Carbonate you add per gallon, whether it be 1/2 teaspoon or 1 teaspoon, simply subtract 0.1 from the starting TA.  Also, add 0.1 to the starting pH.
Adding sugar water to lower TA
Background: Another method for reducing the TA in a must is by adding sugar water.  Assuming there is no acid in your water, this method can be used without affecting the pH of your must.  The important things to consider here are:
  1. most people will prefer to use bottled water for this, but if you live in the country and have a healthy well, that will work fine
  2. it is recommended that you not add more than 15% water by volume to your must ... some sources say 10% ... for most grape varieties.  However, certain varieties such as Catawba and Concord can tolerate an addition of up to 50%.  The more you add, the less body you will have.

There are two computations you will need here.

Calculate water:
  1. Multiply the number of gallons in your must by the current TA.  Remember to use a decimal if you have a partial gallon and if you already treated with Calcium Carbonate, use the reduced TA value.
  2. Divide this number by the desired TA, probably .85.  You don't want to reduce it any more than you have to.  This number is the number of gallons you will have after adding the water.
  3. Subtract the number of gallons you started with from this ... this will give you the number of gallons you will need to add.  Make a note of this number.  You may need it later.
  4. Now multiply this by 128 ... there are 128 ounces in a gallon, so this number is the number of ounces of water you need to add.

Before actually adding this, you should compute to make sure it isn't an excessive amount.  In step 3 above, we noted that you will need that number later.  Divide that number by the number of gallons you started with.  This should not exceed .15, or 15%.  Remember, some prefer to not exceed 10% and Catawba and Concord can handle up to 50%.

Calculate sugar:
  1. Take the Starting Brix (back at the beginning of this page ... probably between 18 and 21) and multiply this by the number of gallons of water you added.  Again, refer back to #3 above
  2. Divide this number by 8
  3. Multiply this number by 2 ... this is the number of cups of table sugar you will need to add to the must to make up for the water you added
Adding a set amount of sugar water to lower TA
Background: I have also found myself in a situation where I wanted to add a set amount of sugar water and then determine what TA this would take me to.
Calculate:
  1. Multiply the number of gallons in your must by the current TA.  Remember to use a decimal if you have a partial gallon and if you already treated with Calcium Carbonate, use the reduced TA value.
  2. Express your new total volume as a decimal ... for example, if you want to add 10%, one gallon is 128 ounces.  10% of this is about 13 ounces ... the total would be 1.1 gallons ... simply multiply  this by the number of gallons you started with.
  3. Divide the number you got in step 1 by the number you got in step 2 ... this is your new TA
Adding acid blend to raise the TA
Background: Occasionally, especially during dry summers, you may encounter a situation where the TA is less than .70%.  In this scenario, you might want to add acid blend to raise the TA.  This is actually a fairly easy computation.  You will need to know the Starting Acid Level, which we will refer to as the SAL.  The Desired Acid Level, or DAL, will probably be .70.
Calculate:
  1. Subtract the Starting Acid Level from the Desired Acid Level ... DAL - SAL
  2. Divide this number by .15.
  3. Multiply this by the number of gallons of must you have.
  4. This will give you the number of teaspoons of acid blend to add.

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