How to use the sulfite campden addition calculator
- Enter the batch volume and choose US gallons, UK gallons or liters.
- Enter the sulfite level you want in ppm, and the level already present if you have measured it.
- Open the advanced options to change the SO2 share of the powder, or to enter the weight of one tablet.
- Read the grams of potassium metabisulfite to add and, if you gave a tablet weight, the number of tablets.
Formula
Liters = volume x liters per unit
Grams = (target ppm - current ppm) x liters / 1000 / SO2 share
Tablets = grams / tablet weight
Level with whole tablets = current ppm + tablets x weight x SO2 share x 1000 / liters
One ppm of SO2 is one milligram per liter. Potassium metabisulfite is about 57.6% SO2 by weight when pure, and the page lets you change that figure.
Five gallons to 50 ppm
A 5 US gallon batch is 18.93 liters. To go from 0 to 50 ppm, 50 x 18.93 / 1000 = 0.946 g of SO2 is needed, and at 57.6% that is 1.64 g of potassium metabisulfite.
If a tablet weighs 0.44 g, the exact count is 3.73 tablets. Four whole tablets raise the batch to about 53.6 ppm.
What the powder does
Sulfite is added to wine, cider and mead to slow oxidation and to limit unwanted microbes. Potassium metabisulfite is the usual powder, and Campden tablets are the same compound pressed into measured doses. The calculator turns a target level in ppm into a weight, taking into account that only about half of the powder's weight is SO2.
Not all the sulfite stays free. Part of it binds to compounds in the batch, and only the free part protects. The amount you measure afterwards is therefore lower than the amount you add, and it falls over time as the sulfite is used up.
Use it as a starting point
The right level depends on the batch, its pH, the stage of the process and what you want to make. Higher pH needs more free sulfite for the same protection. Test strips or a titration kit tell you what is actually present, and you can enter that as the level already present.
This is informational arithmetic. Follow the instructions on your product and your recipe, and observe any limits that apply to you if you sell what you make. Add less than the calculated amount if you are unsure and retest.
Assumptions and limits
- The powder is pure potassium metabisulfite with the SO2 share you enter. A real powder or tablet may differ.
- The ppm is the amount added, not the free level that remains.
- US gallons are 3.785 liters and UK gallons are 4.546 liters.
- Nothing is uploaded.
Frequently asked questions
Why not just add the labeled dose?
The label gives a dose for a standard batch size. The calculator scales to your volume and level so the dose matches what you want.
What is free sulfite?
The part of the sulfite that has not bound to other compounds. It is the part that protects, and it is what a test measures.
Can I use sodium metabisulfite?
The arithmetic is similar but the SO2 share is different, about 67% for the sodium form. Enter the share for your product in the advanced options.
How many tablets for a gallon?
It depends on the tablet weight, your target and the volume. Enter the weight of your tablet and the page counts them.