SULPHITES: ALL YOU NEED TO KNOW, AND THEN SOME.
OK, sulphites are NOT an evil force, out to rob us of our precious bodily fluids, like some people are apt to believe. Au contraire, sulphites can help make our wines taste better and last longer than when we do not add them. But, if a little is good, more is NOT better when it comes to this helpful compound. Here are my beliefs on sulphites.
Potassium meta-bisulfite is better than sodium bisulfite, Although these are used exactly the same way, sodium has more of a chance of coming through in the ultimate flavor, and it IS the older and less commonly-used of the two compounds. Commercial wineries and most of my "semiprofessional" home vintners use potassium meta, and it is all that I use, personally.
Campden tablets are an easy way to add "meta" to an initial must. One tablet per gallon, crushed and pulverized into powder, and stirred into the liquid solution, will give about 50 to 75 ppm sulphite. This is more than enough to knock out all the wildlife that came in from the field and wants to spoil your nice, tasty vintage. Even if you are sulphite scared, (and if you are, please read this) I recommend that you add this initial dosage, because it will be long gone by the time you bottle your product, or even rack it off to another fermenter. (The CO2 that is generated by the fermentation carries off the sulphite gas VERY rapidly.)
Later on, as the wine becomes more and more clear, you do NOT want to add Campden tablets, because the cloudy white filler (that surrounds the tiny grains of meta) will haze up your wine and defeat the whole clarification process that you have been patiently waiting to accomplish. Therefore, Campden tablets are used only at the beginning stages, and later on, you should switch to powdered sulphite.
WARNING: When working with sulphite solutions of any of the following ratios, be very careful NEVER to sniff or inhale the fumes. They will knock you down with their potency. These all have very strong vapors.
Powdered sulphite can be used in three different ways:
1) For an equipment and bottle rinse, mix 1 ounce of powdered meta with one gallon of good, clean water. This "diluted" solution can be used to rinse bottles, carboys, tubing and anything else that you might want to give a good cleaning to before the wine comes in contact with it. The equipment can then either be left to air-dry, or used immediately after the excess drips out. (This leaves a residual sulphite layer as a protectant in your bottle... which is good!)
2) As a "direct-dosage" solution, (for adding meta-bisulfite directly into your wine) 1 ounce of meta powder should be mixed into 8 fluid ounces of water. Mix well, until dissolved. One teaspoon of this "concentrated" liquid solution is equal to one Campden tablet. Five teaspoons in 5 gallons of wine will give approximately 75 ppm sulphite, an average, good dosage.
3) Or, for those that do not like to mix solutions, 1/4 TEASPOON of straight meta powder can be added to 5 gallons of wine and it will give a dosage of 50 ppm. DO NOT ATTEMPT THIS WITH SMALL AMOUNTS OF WINE. You cannot measure precisely enough. Use this method only when you have 5 gallons or more - preferably more.