Potassium Metabisulfite in Winemaking

updated 02/17/2025

Periodically newcomers to WineMakingTalk who state they:

• Want to make wine “naturally”
• Don’t want to use “chemicals”
• Don’t want to use “sulfite”

There’s a lot of folks proselytizing ideas regarding back to nature and removing chemicals from our lives. A lot of this is good and makes sense, but a fair amount is lacking in facts, science, and/or reason. For people who are just learning, it is often difficult to determine who is right and who is not.

Side note: Folks should research things well before making any decisions in improving health and diet, and not use just one source. Just ‘cuz ya read it on the net (or in a book) does not mean it’s correct. My 7th grade social studies textbook said Nathan Hale (American Revolutionary War figure) died in 1776 and was born in 1783, which I am positive is incorrect.

This post focuses on sulfite, explaining my understanding of why and how it is used in wine.

Note: Potassium Metabisulfite is commonly referred to as “K-meta”, as “K” is the atomic symbol for potassium.

Important Note: My posts, including this one, are a result of personal research, conversations with other winemakers (both amateur and professional), and practical experience over decades. I explain what I do and (most importantly) why I do it. My intention is to provide information that others can use in making their own decisions.

What K-Meta Is Not

As stated above, K-meta is Potassium Metabisulfite. It’s common for beginners to mistakenly use the terms “sulfate” and “sulfide” instead of “sulfite”. These are completely different compounds that are not and should not be used in winemaking.

Sodium Metabisulfite was used in winemaking for many years, but has been replaced by K-meta. Among reasons given for this is to reduce sodium intake for health reasons, and that in larger doses sodium metabisulfite can produce a salty taste. Commercial wineries in the USA are not allowed to use sodium metabisulfite, and while home winemakers can use it, it’s generally recommended to use K-meta.

When Not to Use K-Meta

While K-meta in reasonable amounts is perfectly safe for most people, some people have a sensitivity or even allergy to sulfites. I say “sulfites” here because there are many types of sulfite.

If the home winemaker or any drinkers of that wine are allergic to sulfites, then it should not be used. This will have an effect upon the longevity of the wines (see below), but excluding it may be absolutely necessary.

Note that wine contains a natural amount of sulfite that varies by varietal and situation, so anyone allergic needs to use caution. Anyone believing they are allergic should see a doctor regarding this. This is not medical advice, just common sense.

Benefits of K-Meta

While K-meta is often referred to as a “preservative”, it performs three useful functions:

• Anti-oxidant
• Anti-microbial
• Anti-contaminant

Anti-oxidant. Oxygen oxidizes wine, in a fashion analogous to steel rusting, and oxidized wine is about as useful as rusty steel. K-meta binds with oxygen (O2), rendering it harmless. Unless you have a very high-tech setup, there’s no way to keep O2 completely out of wine, so K-meta is added to neutralize any present O2.

Anti-microbial. K-meta kills or stunts a wide variety of microbial life, preventing unwanted organisms from thriving in wine. This allows the yeast to thrive and fulfill it’s mission to make wine. Post-fermentation sulfite continues to produce a hostile environment for microbial life that can survive in the already low pH environment.

Anti-contaminant. Similarly to what it does with O2, K-meta binds with many other “contaminants” (unwanted substances), rendering them harmless. A notable one is hydrogen sulfide (H2S), which may be produced if the yeast is stressed. I have been asked why they should add more sulfur to treat sulfur — this is not correct. Sulfite is being added to treat sulfide.

When K-meta is added to wine, it ionizes to produce free SO2, which combines with the above items, rendering them harmless. I generally refer to all items that SO2 neutralizes as “contaminants”.

This typically increases longevity (shelf life) and may improve overall quality.

Since SO2 renders contaminants harmless, it reduces or eliminates things that cause wine to age prematurely. Wine changes throughout its lifespan, from the moment the fruit is crushed to when the wine is consumed or binned because it aged beyond drinkability. Wine improves to a certain point (depending on too many factors to list), then it starts declining. SO2 moves that point farther out, which increases the shelf life.

Note: Sulfite is not the only factor in increasing wine longevity. Higher levels of ABV (Alcohol By Volume), residual sugar, acid, and tannin may also increase longevity.

Additionally, this same action may improve wine quality. For instance, oxidation produces aroma and taste that is mostly considered objectionable. By preventing oxidation, the wine is palatable longer.

We must keep in mind that every wine has a finite lifespan. It’s best to drink wines before or at their peak, and when they start to decline, drink ’em up.

Using K-Meta

The rule-of-thumb I was taught in 1984 is to use 1/4 tsp K-meta powder in 19 to 23 liter of wine. K-meta is added:

• 24 hours prior to inoculation to kill or stunt wild yeast and other microbial life (optional).
• At each post-fermentation racking.
• Every 3 months during bulk aging.
• At bottling time.

Why are repeated treatments necessary? The free SO2 is consumed as it neutralizes contaminants, so it must be refreshed.

This rule has not changed in 40+ years that I’ve been making wine. I theorize that it came from decades of practical experience. It was recognized that K-meta is beneficial to the wine, and thousands of winemakers experimented with amounts. Given limited resources, winemakers of the past would use only as much as necessary, as more is a waste of valuable resources. In some fashion, “1/4 tsp per 19-23 liters” became the accepted rule.

In my experience, it works.

SO2 Testing

I don’t do SO2 testing. It’s relatively expensive and I simply don’t see the need. The “1/4 tsp rule” works, my wines don’t oxidize, and I have more than sufficient longevity.

SO2 is more effective in a lower pH environment, so if the pH is high (after I adjust by taste), I may add a bit more K-meta to address the need.

Some folks try to fine tune the amount of free SO2, but I view that as herding cats. Sunlight, O2 exposure, microbial exposure, simple chemical changes from aging, etc. all affect the amount of SO2 that is consumed. There are too many uncontrollable factors, so I don’t bother trying.

Note: I’m not telling anyone to NOT do SO2 testing. If anyone feels it brings value, then do it.

Odd Batch Sizes

It’s common for home winemakers to make batches of 4, 19, or 23 liters, translates to 1, 5, and 6 US gallons. [I typically work in metric as it’s more precise and less ambiguous than US or Imperial measurements.]

Campden tablets provide 50 ppm SO2 (standard dosage) for 4 liters. It’s necessary to crush each tablet to powder. Folks that don’t get bits of the white tablet coating in their wine, which is harmless but disconcerting.

Crushing tablets to dose 19 and 23 liter batches is time consuming to get a fine powder, and Campden are more expensive than powdered K-meta.

I make mostly grape wines, and my batch sizes vary a lot. It’s common for me to have a 55 liter barrel of wine plus odd 19 and 23 liter carboys and 4 liter jugs. Dosing the large containers is relatively simple. For the 4 liter jugs I do the following:

1. Measure 5 to 6 Tbsp water into a sanitized container.
2. Add 1/4 tsp K-meta; mix well.
3. Add 1 Tbsp solution to each 4 liter jug.

Getting the solution to mix into the wine can be difficult. I often withdraw an amount of wine using a wine thief, which is put into a sanitized container. I then add the K-meta solution, then the reserved wine. This doesn’t mix perfectly, but appears to do well enough.

Conclusion

This post explains what K-meta is, what it does, and the benefits it brings to the table. This should provide sufficient information in deciding what to do with their wines.