In the May issue of “Pressing News” Scott Irwin provided readers with an understanding of sulfite and its important role in winemaking. If you have not read his article, you should do so before reading this. In this article I would like to help make those sulfur dioxide (SO2) additions a little easier.

I believe the best the winemaker can do is to be in the ballpark. Test equipment and measuring equipment can help us get closer. But after all, we are we are trying to make adjustments to something measured in parts per million (ppm). The limited capability of the teaspoon will become quickly evident if a small adjustment is needed or small batches of wine are being made.

Most kit instructions indicate that you should add ¼ teaspoon of potassium metabisulfite per 6 gallons if you plan to age the wine more than 6 months. How much potassium metabisulfite is in that quarter teaspoon? Some sources say 1.4 grams others 1.6 grams. In 6 gallons, that is an addition of between 35ppm and 40ppm SO2. That’s in the ballpark, which makes this single addition of SO2 easy for kit wines.

What if you are conducting an experiment and have split the kit into 6 one-gallon batches. How do you measure one-sixth of one-quarter teaspoon? If you make a scratch wine, it is often recommended that the Must be sulfited to 50ppm (about 1/16 teaspoon per gallon). If you test the free SO2 and find it to be 15ppm and you want 30ppm, how much do you add?

In theory, Campden tablets would seem to be an easy way to add SO2. After all, what can be easier than one tablet per gallon? Scott ran a series of tests on two different brands of Campden tablets and found up to a 60% variation in the amount of free SO2 that was added. In my own experience I have found that Campden tablets from different sources vary widely in the amount of SO2 added. Although easy, they may not be a reliable method of adding SO2. Campden tablets could leave you in the parking lot rather than in the ballpark. What’s a winemaker to do?

The solution is a solution. By preparing a 10% metabisulfite solution you can deliver a more reliable and consistent addition to the wine or must. Note that using a 10% solution will not be exact, it will only be in the ballpark. Since potassium metabisulfite is about 57% SO2, a 10% potassium metabisulfite solution is about 5.7% SO2. If you use sodium metabisulfite, your percent of SO2 will be slightly higher.

This is how I prepare my solution. I weigh out 70 grams of potassium metabisulfite. I then mix this with water to total 700 ml using a graduated cylinder. Although this seems like a lot of 10% metabisulfite solution, I put 500ml in a gallon jug and fill it with water to be used as a sulfite rinse solution for my equipment and bottles. The remaining 10% solution is used for adding to the must or wine.

Since each milliliter of 10% solution contains about 100 milligrams of metabisulfite, I make my additions at the following rates:

One ml in one liter adds 57ppm of SO2

One ml in one gallon adds 15ppm of SO2

One ml in 5 gallons adds 3ppm of SO2

One ml in 6 gallon adds 2.5ppm of SO2

To obtain the equivalent of a ¼ teaspoon of potassium metabisulfite in 6 gallons, I add 15ml of my 10% solution. For 50ppm in the must of my gallon batch of scratch wine, I add 4ml of solution. To make an addition of 15ppm in 6 gallons, I will add 6 ml of solution. I know that it is not exact, but I believe it is close enough.

Don’t have a scale capable of measuring grams? Don’t want to invest in graduated cylinders? Do you still want to be in the ballpark? Read on.

Most home wine shops sell potassium metabisulfite in 2-ounce quantities. Mix two ounces with water to obtain a total of 19 fluid ounces and you have a 10% solution. Dilute one part of your 10% solution with 7 parts water, and you have the recommended 1.25% sulfite solution for sanitizing equipment and bottles. One teaspoon of the 10% solution is about 5ml and one tablespoon about 15ml. One teaspoon can be substituted for one standard Campden tablet adding about 75ppm of available SO2 per gallon.

I did obtain a scale and graduated cylinders because I thought I could be exact with my SO2 additions. I did however; come to the understanding that the best I could hope for was to be close before investing in pipettes to measure my additions. To measure my additions I use an extra syringe designed for acid testing (about $1.25). Make sure it is clearly marked so you don’t mix it up with the one you use to measure sodium hydroxide. SO2 in wine is okay sodium hydroxide is not.

I have found the solution to be easier than trying to weigh milligrams of metabisulfite powder. It is better than the inconsistent quantities encountered with Campden tablets. And I believe it gets you in the ballpark.

Joseph Schuitema - Dallas, Texas