Initially, Campden Tablets are used to kill off any potentially harmful bacteria that may may be present in the base ingredients used in winemaking, and to discourage any wild yeast from gaining a foothold. Campden will not kill yeast, but it creates an environment inhospitable to them. As sulfur dioxide (SO2) is released into the must and the atmosphere above the must dissipates, the environment inside the fermenter slowly changes and the yeast can grow, but by then our cultured wine yeasts, which are more tolerant of SO2, have gotten a good start and “crowd out” the wild yeasts, use up all the dissolved oxygen, and consume all the fermentable sugar and nutrients. In the end, there is nothing left for the wild yeasts and they die without propagating.

When we rack, we add oxygen to the wine and expose it to airborne microorgamisms we’d rather keep out of the wine. This causes the wine to oxidize if antioxidants are not present to prevent it from happening. SO2 is a powerful antioxidant but it dissipates over time, so we add more Campden to the wine when we rack to prevent oxidation. The same antioxidant protects the wine from airborne bacteria and molds.

Campden is also added to the carboy at the time of the 1st racking, the 3rd racking, the 5th racking, and so on. We skip the 2nd, 4th, 6th, etc. rackings unless one of them is the last racking before bottling. We always add Campden (or metabisulfite salt) at the last racking because the wine is particularly vulnerable to infection (from the air, inside the bottle or on the cork) when bottling it.

Which one to use?

The main difference between the sodium (SMS) and potassium (KMS) metabisulfites is the carrier element.

Their effects are virtually the same, with sodium metabisulfite being slightly more potent when it comes to contributing SO2 gas. Most home winemakers will use sodium metabisulfite as an equipment sanitizer as it is cheaper.

SMS = sanitizing
KMS = actual treatment of the wine

Steps to Use Campden Tablets

1. Initially, crush the Campden tablet with a glass mortar and pestle and stir the powder directly into the must.
2. Before racking, crush the tablet and pour the powder into 1/3 cup of HOT water. Use a sanitized bamboo whip or a stainless steel fork to beat the powder into the water. It may take a few minutes, but it will all dissolve if you work at it. This cools down the water quite a bit.
3. When dissolved, use a wine thief (or siphon tube) to draw off a cup or so of wine and mix this with the sulfited water. This sometimes causes small lumps to form, so whip the mixture a little more and then pour it into the receiving jug or carboy.
4. Then rack the wine into the secondary.

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