New home winemakers often get confused between potassium metabisulfite and sodium metabisulfite. Some winemaking guides only refer to sulfite and it’s up to the reader to try to understand which form of sulfite the author was referring to. What’s the difference? And does it really matter?
Both potassium and sodium metabisulfite are used as sanitizing agents and as additives to wine to protect it from oxidation and to inhibit bacteria growth. When used in a solution with water, both can sanitize winemaking equipment and the workspace where wine is being made. When added directly to wine in small amounts, it releases sulfur dioxide (SO2) gas which is what protects wine from oxidation and micro-organisms.
Potassium metabisulfite, which is sometimes abbreviated as KMS, K sulfite, and K-meta, comes in a powder form. The sodium version is available in powder as well as tablets which are usually referred to as “Campden Tablets.” Some suggest that KMS and sodium metabisulfite are exactly the same, however this is not completely true.
Although they can be used interchangeably for the same purposes of sanitizing and preservation, those on a restricted sodium diet should try to use only potassium metabisulfite in their wine. Another difference is that the sodium version can contain a slightly smaller amount of sulfur dioxide.
When purchasing a , the type of sulfite that is included which is to be added to the after it has completed fermentation is potassium sulfite. It is best to follow the directions exactly and add this to your wine in order to protect it during the degassing stage, prior to clarifying and bottling. If you are planning on aging your wine for a couple of years or more, you may want to consider adding an additional amount of KMS prior to bottling or while it is bulk aging in the carboy.
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To keep wine from becoming spoiled winemakers sometimes add preservatives. In fact, if preservatives are not added to wine it will only last six months to a year. Preservatives are added to keep wine from turning to vinegar and several types of preservatives are used in the winemaking process.
Two natural preservatives result from the grapes and the fermenting process – alcohol and tannins. These preservatives are excellent for extending the life of wine and kill off most organisms as very few can live in alcohol.
The most popular added preservative is sulphur dioxide. This is an anti-oxidant and a sterilizing agent that prevents organisms from growing in wine. It also prevents wine from turning into vinegar. This occurs by forming a barrier between oxygen and the wine, not allowing them to interact.
If the Romans Can Do It…
Sulphur has long been used as a preservative. In ancient times the Romans broke sulphur into small pieces and burned it before adding the pieces to wine. It also has a long history as a food preservative since the early 18th century.
White wines normally have more sulphur dioxide because they are sweeter. Sweet wines contain more sugar and ferment at a higher rate, resulting in a need for more sulphites.
Other common preservatives include 220 sodium dioxide, 220 sodium bisulphite, and 223 sodium meta- bisulphite. As with sulphur dioxide, these sulphites are regulated as to the amount that can be added to wine.
Why the Aging Process Needs Preserving
Preservatives added to wine depend on several factors. There are many things that can take place at the winery or during harvesting that lessen the amount of preservatives needed. For example, careful harvesting of grapes will keep them from being damaged. That is why some of the best vineyards pick grapes by hand.
It is very important to time the harvest process correctly. The time between the harvesting of the grapes and the time the grapes arrive at the winery is critical. Less of a time interval at this stage means less opportunity for bacteria growth and less need for pesticides.
Cooling processes are necessary. All wineries must have temperature sensitive cooling equipment in order to keep grapes at the proper temperature during the winemaking process. This is especially important when the grapes are being crushed.
Winemakers use a special filter to remove organisms from the wine. This filter acts as a screening device. The filtration system is used before the wine is boiled during the winemaking process.
Cleanliness is Next to…Great Wine!
A clean winery is important for preserving wine. Winemakers strive to keep their facilities as clean as possible in order to keep bacteria to a minimum. This keeps other harmful items from entering the wine at anytime during the winemaking process. Common logic says that the cleaner the winery, the less preservatives needed to keep harmful microbes at bay.
The cleanliness of winemaking facilities has lead to the theory that overall, cheaper wines have a higher sulphur count than higher quality wines. This is due to the clean conditions of high end wineries and the high expectations of their customers.
A preservative free wine does not exist. Many people are confused over terminology and feel that a wine must be preservative free in order to be organic. The preservatives added to wine have nothing to do with its organic status.
An organic wine is produced using harvesting methods that are eco-friendly. In addition, certain of the winemaking processes may also be eco-friendly but the adding of preservatives does not make a wine non-organic.
Do not concern yourself with the safety of sulphites in wine. The preservatives are not harmful and even allergies to sulphites are extremely rare. As mentioned before, no wine is entirely sulphite free. Even if sulphite is not added during the winemaking process the grapes themselves produce a small natural amount.
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