Potassium metabisulfite comes with just about every wine kit and is used as an additive even in wineries.

This article explores what potassium metabisulfite is and how it works. To learn how to figure out how much to add to your wine check out Adding Potassium Metabisulfite to Wine (includes a calculator).

But what does it do? What is it for? Is it safe? Let’s find out.

What is Potassium Metabisulfite?

Antioxidant and preservative potassium metabisulfite.

Recommended Potassium Metabisulfite (affiliate)

Simply put it’s an antioxidant. It slows down the aging, i.e. oxidation, of wine by removing free oxygen suspended in the wine.

Oxygen is both harmful and beneficial to wine. It is harmful in large quantities because it rapidly accelerates the aging process. However, wine starved of all oxygen can develop off flavors.

The solution? Remove all oxygen suspended in the wine, bottle it, and let tiny amounts back in through natural cork closures. This is what we call micro-oxygenation.

Potassium metabisulfite is often called a stabilizer because it serves to prevent spoilage and further fermentation by removing oxygen. However, this serves another purpose it preserves the flavor and color of a wine.

An over oxidized wine can taste cooked or flabby (lacking body). Additionally, an oxidized wine turns red wines orange and eventually brown. White wines turn a golden brown color.

This additive is available in a powdered form as pictured here as well as in tablets called campden tablets (affiliate links).

Potassium metabisulfite may also be used as a sanitizing agent due to its antioxidant properties.

How Does it Work?

When you dissolve PM (K2S2O5) in water it forms three different compounds, sulfur dioxide, bisulfite, and sulfite. Each of these is able to bond with free oxygen floating around in wine. When this happens the free oxygen is no longer available to be consumed by micro-organisms.

The removal of oxygen chokes off most micro-organisms and will prevent them from reproducing. It does not, however, stop a fermentation. Yeast produces alcohol only when forced to live without oxygen but it does go on living. Read this post for more information on the how yeast is used to make wine.

By adding potassium metabisulfite after you’ve stopped fermentation completely you can then back sweeten a wine with little risk of rekindling the fermentation of newly added sugar.

A Common Misconception

  • Sodium Metabisulfite can be used interchangeably with potassium metabisulfite.

While they both have very similar chemical makeups the difference is that potassium metabisulfite leaves potassium behind and sodium metabisulfite leaves sodium behind.

Potassium occurs naturally in grapes and is essential to their growth. So adding a bit more potassium to the mix isn’t going to hurt anything. There’s already some in your wine.

Sodium on the other hand is not something we want to add to our wine. Can you see yourself pouring table salt into a glass of wine? No. Don’t use sodium metabisulfite.

Things to Be Careful of When Using Potassium Metabisulfite

There are a few things you should know about potassium metabisulfite before you use it again. First, the compounds it creates can be hazardous to your health in large quantities.

SO2 is a toxic gas to breath. It can cause breathing difficulties, swelling, rashes, and difficulty swallowing. If you feel any of these go for help.

Be careful not to breath the dust in or gas that is released when dissolving in water. I’d also steer clear of sipping on any samples immediately after adding this to your wine. Give it time to bond with the oxygen.

Potassium metabisulfite is a controlled substance in food and wine preservation. There are strict legal guidelines on concentrations that are allowed in the final product.

This all sounds scary and I don’t mean to come across that way but it is important to know and understand the nature of the chemicals we’re using in our wines. Wine kits and packages from winemaking stores don’t often come with any sort of precautions or warnings. So I thought I’d fill you in.

Now before you decide you’re not adding this to your wine because it’s so nasty think about this. The compounds created by dissolving potassium metabisulfite readily bond to free floating oxygen and create new compounds.

These new compounds are not nearly as scary. Even so the concentration of the new compounds in your finished wine will be so small that they will not be noticeable to the consumer.

It’s only bad for us in it’s pre-mixed state. So don’t worry. It is very beneficial to the color, flavor, and longevity of you wine.

Now that you’ve gotten a proper introduction to this additive check out, Adding Potassium Metabisulfite to Wine, which explains how to calculate the proper addition for your wine.

  • Juan G. Voss

    Hi Matt,

    Thanks for all the explanations.
    I made a batch of white merlot and Tempranillo with grape skins both from WINEXPERT. In both cases they are still bulk aging, and started smelling a sherry aroma and from what I read is related to oxidation. I added Potassium Metabisulfite as per pack instructions and everything seems ok now.
    But I have a question regarding bottling. I read that is also required to coat the bottles and cork with a solution of PM and water. I was wondering if you had idea what kind of concentration is required. Also, assuming that my bottles are clean, after I coat the bottle do I have to bottle the wine immediately? should I rinse the bottle or wait until the solution dries?
    Thanks again for posting all these articles.

    Cheers,

    Juan
    I started sniffing off-aromas

    • Hi Juan,

      Thanks for the comment and questions. Sherry aromas can indeed indicate oxidation. The unfortunate thing about oxidation is that there’s little you can do once it sets in. Adding the potassium metabisulfite was a smart move. That served to get rid of any oxygen in your wine that had yet to oxidize anything.

      Before bottling I would suggest tasting a sample of the wine to make sure its tastes ok. If it does then proceeding to bottling as soon as possible is definitely a good idea. I recommend using a sanitizer such as Star San as opposed to potassium metabisulfite. Star san actually kills micro-organisms while the potassium metabisulfite just removes oxygen.

      Here’s my bottling workflow:

      1. Clean bottles and equipment with a bush and warm water.
      2. Dip all bottles and equipment in Star San for about a minute and let them drain on a bottle tree or sanitized dishwasher rack.
      3. Fill the bottles with wine using the bottle filler.
      4. Dip the corks into Star San for 15-30 seconds and insert into the bottle with a corker.

      How long has your wine been bulk aging? Was it aged on the dead yeast or was it racked into a clean carboy after all the sediment had dropped out?

      Cheers!

      Matt

      • Juan G

        thanks Matt,

        The wines (Tempranillo and White Merlot) still taste a little like grape juice.

        The tempranillo has been bulk aged in a clean carboy without dead yeasts since Dec. 2012. I have added oak chips and cubes (french and american). I plan to bottle more or less in a month.

        Regarding the white merlot, it was finished in February 2013, and it was filtered. I plan to bottle also in the coming weeks.

        Cheers,

        Juan

        • Matt

          Hi Juan,

          I’m glad to hear that both wines are still in good shape. Mixing the French and American oak is a terrific thing to do! I’ve got an experiment in mind doing something similar to the Great Riesling Yeast Experiment but with oak.

          Thanks for the great questions and for asking them in the comments where others can benefit from the discussion.

          Cheers!

          Matt

  • John Oman

    I don’t understand why PM is not a sanitizer. When I sanitize my hands with it there is an immediate stinging from any small cuts I may have. Also, the PM I use(Crosby & Baker) includes equipment sanitizing mixture instructions. I have never had a problem using it as a sanitizer.

    • Matt

      John,

      Thanks for the question. I had asked the same thing of a local wine supply shop when I was getting into this and they had told me that it doesn’t really sanitize but just removes oxygen. However, after you asked the question I did some additional research and found that a lot of people do use PM as a sanitizer at an increased concentration.

      Based on your experience and what I’ve read elsewhere today I stand corrected! I’ll update my post accordingly. Thank you for letting me know.

      Cheers!

      -Matt

  • Anthony Reyes

    Excellent information. I’ve recently started making wine about a month ago and enjoying it greatly. I use Star-San as a sanitizer and I like it more than PM, mainly due to 1/8 oz. makes 1 gallon of sanitizer. If you are cost conscience then Star-San is the way to go, due to the large amounts you can make with one $10 bottle of Star-San. Great information and keep on brewing!

    • Matt

      Thanks for the comment Anthony! I too am a fan of Star-San. A little does go a long way and you don’t have to worry about it not dissolving all the way.

      Cheers!

      -Matt

  • Mike

    Hi Matt, I didnt realize there was a difference, and I have added sodium metabisulfite to my wine for aging. From your article, it looks like I should have bought and used potassium metabisulphite. Should I go ahead and add the potassium meta now or should I just leave it be as is before bottling.

    • Hi Mike, that’s a really good question. I do not recommend adding at the potassium metabisulfite at this point.

      The most important part of either additive is the sulfites. Potassium and sodium are used to bind SO2 gas and keep it in a solid form. Once it hits your wine and dissolves the SO2 gas is released and we no longer have any use for the potassium or sodium.

      If you were to add potassium metabisulfite on top of sodium metabisulfite I would worry that your sulfite levels would be too high. You would then need to test your wine to determine if the sulfite levels are safe for you to consume the wine.

      Sodium metabisulfite can impart a salty taste over time but likely this won’t happen with just one dosage. If you plan on doing subsequent sulfite additions I would then recommend switching to potassium metabisulfite but if that was the last dose then don’t worry about it.

      I hope this helps Mike!

      Matt

      • Mike

        Thanks Matt. I will heed your advice and leave that batch alone. More importantly, I will know for my next batch to use potassium metabisulphite.

  • Gary Beaumont

    After Matt`s help I now have Pot met to use 🙂 also have stopped adding any pot sorbate as my wine finishes at .992 to .990 and as i`m not back sweetening so decided not to use it.

    • Gary, thanks for sharing your experience! Avoiding sorbate is a good idea when you can. I was really surprised when I found out what it can do to the flavor and aroma profiles long term. I truly believe that the more we know about the wine making process and the additives that go into it the better our wines will be. I hope this is your experience as well.

  • Mark

    I added yeast yesterday and forgot to add potassium bisulfate I just added it. Is it going to be ok to add yeast for a second time after 24 hrs?

    • Hi Mark, great question! The potassium metabisulfite is used to stabilize the must is to know out any stray micro-organisms to compete with. Wine yeast just happens to be strong enough to deal with reasonable levels of sulfites so there’s a chance that the yeast you’ve previously added.

      I would recommend giving the must a little time to see if the first dose of yeast can power through the sulfite dosage. The good news is that your wine will be protected from everything else too so you aren’t at a great risk of spoilage or other micro-organisms.

      You can pick up yeast flavors in a finished wine if you add too much yeast to the must. Giving the must 24-36 hours or so to see if fermentation begins shouldn’t hurt anything and may help you avoid yeast flavors in the finished wine.

      Please let me know how it goes for you and what you decide to do. Cheers! -Matt

  • Hi Daniel, great question. Campden tablets are actually just potassium metabisulfite packaged in a premeasured “pill”. It can stop fermentation with weaker wild yeast strains but for the most part traditional wine making yeast strains should be able to withstand most normal sulfite levels.

    In general the best way to stop a fermentation is to use a sterile filtration system. Filters with a mesh of 0.45 microns or finer will actually remove single celled organisms from your wine, yeast or spoilage organisms.

    I hope this helps Daniel! -Matt

  • larry

    question: i make my own homemade wine from a kit…I accidentally added the potassium metabisulphite at the same stage as i would add yeast…will this harm the wine (merlot)

    • Hi Larry, very good question. Wine making yeast is one of the only micro organisms that can survive the sulfites used to stabilize a wine.

      This is why you’ll often see fruit wine recipes that call for sulfites be added to the fruit juice 24 hours before you add the yeast. The sulfites kill off the wild yeast and spoilage micro organisms and allow the wine yeast to come in and dominate the fermentation.

      Was the sulfites supposed to go in after fermentation per your kit instructions? -Matt