Sulfite

Sulfite (also known as SO₂) is used in both wine and beer for its oxygen-scavenging ability and its anti-microbial effects. Its use extends back for millennia. It can also be used for removing chlorine and chloramine from water or for no-rinse sanitizing.

According to the International Union of Pure and Applied Chemistry (IUPAC), the standard spelling is "sulfite". However, "sulphite" is still commonly used in the UK.

Sulfite should not be confused with sulfate or sulfide.

Sources of Sulfite

Sulfite is produced naturally by yeast during fermentation, and may be present at the end of fermentation in some amount, usually less than 30ppm although some strains can produce as much as 300ppm. The yeast produce sulfite by reducing sulfate, although the concentration of sulfate may have only a minor effect on the amount of sulfite produced. As an aside, yeast also produce compounds during fermentation that bind to sulfite, decreasing the proportion of free SO₂.

Sulfite is available in powdered form as sodium metabisulfite and potassium metabisulfite, and also in tablet form with the brand name Campden. These products are not fully interchangeable.

• Sodium metabisulfite (Na₂S₂O₅) is 67% SO₂ by weight. The sodium can affect flavor, although not necessarily in a negative manner. It is also known as SMS or Na-meta.
• Potassium metabisulfite (K₂S₂O₅) is 58% SO₂ by weight. The potassium is flavor neutral, so it is preferred in winemaking. Potassium also helps wine my serving to help precipitate tartrate salts. However it may be less favorable in beer brewing because high levels of potassium are known to inhibit enzymes during the mash. It is also known as KMS or K-meta.
• Campden tablets come in differing strengths and can be either sodium or potassium metabisulfite. Be aware of what you are actually using.

Proper Storage

Because sulfite reacts with oxygen, it needs to be stored in an air-tight container with as little air and moisture exposure as possible. The shelf life is limited to 6-12 months.

Chlorine Removal from Water

If you are making a wine or beer using tap water containing chlorine or chloramine (e.g. from a municipal water source), adding a small amount of sulfite is an easy way to remove it. This is important because yeast may produce chlorophenols when in the presence of these chlorine compounds, which contribute an off-flavor commonly described as plastic like Band-Aid, even in tiny amounts. Therefore the sulfite needs to be added at any point in time before aerating and pitching yeast.

Campden tablets are particularly convenient for removing chlorine or chloramine from tap water, where the dose needed is small and precision is unimportant. Use as directed; normally 1 tablet treats 20 gallons of water. That equates to 0.022 grams of sodium metabisulfite per 1 US gallon.

Sulfite Usage in Wine

Because of its utility, sulfite is an extremely common additive in commercial wines as well as homemade wine. It can be added at different points in the process to achieve different goals. Sulfite is practically a necessity for a wine that will be aged.

Legislation limits the total amount of sulfite that can be added to a commercial wine. This is not an issue for home brewers that avoid using rotten fruit; sulfite is safe to use in reasonable quantities.

Pre-Fermentation Sulfite

Sulfite can be used pre-fermentation to kill or inhibit wild microbes naturally present on the fruit. Its use is entirely optional, and if the must/juice/honey/etc is pasteurized, then sulfite is definitely not necessary because there are no wild microbes present.

The wild microbes can certainly be beneficial for wine, so the winemaker should consider the options carefully.

Targeting a molecular SO₂ of 1ppm or higher is generally considered acceptable for inhibiting the widest range of microbes to the highest degree needed. A lower amount (such as 0.5ppm molecular SO₂) may be used to only partially inhibit the wild microbes, which may still allow some of their beneficial effects. If using sulfite pre-fermentation, the pH should be adjusted to no higher than 3.8.

Prior to pitching yeast, the must needs to be thoroughly aerated to neutralize the sulfite so that it doesn't affect fermentation.

Post-Fermentation Sulfite

Sulfite is used post-fermentation to protect the wine during aging both by preventing oxidation as well as inhibiting microbial activity.

Sulfite should be added after the primary and any secondary fermentations are completed. Depending on how long the wine is aged and how it is handled, sulfite levels may need to be increased periodically. SO2 testing is very helpful for making the determination as to when additional sulfite is needed and how much.

The level of free SO₂ should generally be maintained in the 50-100ppm range during aging. Molecular SO₂ should be maintained above 0.5ppm. After the wine is packaged, the sulfite level will continue to decline.

The ultimate goal is to have the molecular SO₂ level around 0.6-0.8ppm and free SO₂ no higher than 100ppm at the time the wine is consumed. Levels of molecular SO₂ above 1.0 or free SO₂ above 100 may cause faults. In particular, a high level of molecular SO₂ causes a noxious choking sensation when inhaled.

Sulfite should always be used when stabilizing a wine by adding sorbate. This helps prevent off flavors from developing.

Sulfite Usage in Beer

In low oxygen brewing, sulfite is frequently used for its ability to actively scavenge oxygen and prevent oxidation.

Oxygen Scavenging

Sulfite is most commonly added immediately before dough-in to help prevent oxidation during wort production. The commonly suggested starting amount is 20-30ppm of sodium metabisulfite, which equates to 13-20ppm free SO₂. This sulfite is always fully neutralized (into sulfate) and does not persist into the final beer. SO2 testing ideally should be utilized to track oxygen exposure during the wort production process and optimize the usage rate.

Outside of the context of low oxygen brewing, sulfite is not used in beer production. Furthermore, sulfite is never used in commercial wort production because the scale of commercial systems can much more efficiently limit oxygen exposure during the process.

Post-fermentation sulfite may be added when packaging to help delay oxidation during aging/storage. It can be used even when not utilizing a low-oxygen process of wort production. Anecdotes suggest that this may even be used when bottle conditioning without any ill effects.

Microbial Effects

The pH of beer is typically too high for sulfite to have any anti-microbial effects, especially at the low amounts that are commonly used.

On rare occasions, home brewers have used sulfite as a way to stabilize wild microbe flavor production in sour beer.

Residual sulfite at the time of pitching yeast has been reported to frequently cause the production of hydrogen sulfide by the yeast (in low oxygen brewing).

Sanitizing

Sulfite solution can be used as a no-rinse sanitizer. Go to sanitizers for more information.

How Sulfite Works

(In progress)

Sulfite Sensitivity

Let's not beat this dead horse. Here are some articles:

• https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4017440/
• https://winefolly.com/tips/sulfites-in-wine/
• https://www.wired.com/2015/06/wine-sulfites-fine-heres-remove-anyway/
• https://www.scientificamerican.com/article/myths-about-sulfites-and-wine/
• https://edis.ifas.ufl.edu/fy731

Additional Resources

http://www.techniquesinhomewinemaking.com/attachments/File/SO2%20Management%20Protocol.pdf

http://www.techniquesinhomewinemaking.com/home%20winemaking%20resources.html

http://www.brsquared.org/wine/Articles/SO2/SO2.htm