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?
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.
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.