Sulfites are added to wines to help protect them from spoilage and from the effects of oxidation. This is true for homemade wines as well as professionally made wines. Without sulfites the wine can eventually becomes host to a mold or bacteria growth such a vinegar, or lose its color and freshness.
When adding sulfites to wine we use either Campden tablets, potassium metabisulfite or sodium metabisulfite. Each is essentially the same thing in a different form. These sulfites are simple to add to a wine, but there are some things you should know about using them.
Sulfites Are Funny
In reality sulfites are a little funny in how they react to a wine or wine must. When adding a sulfite to a wine, not all of it wants to stay there. Some of the sulfite wants to leave – escape like as a gas, much like CO2 carbonation wants to escape from a bottle of soda pop. It take time for the free SO2 to leave the wine, but eventually the amount of free sulfite in the wine will be only minor.
The other half of this story is that while a portion of the sulfites leave the wine as a gas, known as free sulfites, there is another portion of the sulfites that want to stay. These are the sulfite molecules that actually bond to the wine and are quite comfortable where they are. This portion is known as bound sulfites.
Here’s The Twist…
Even though some of the sulfites stay in the wine, you still need to replenish the wine with additional doses of either Campden tablets, potassium metabisulfite or sodium metabisulfite. This is because the bound sulfites that remain in the wine have no ability to protect it. They do nothing. They are just there.
- Before the fermentation
- After the fermentation
- Right before bottling
By adding sulfites at these three time you are making up for the free sulfites that have left.
Why Does All This Matter?
It matters because it is possible to add too much sulfites to a wine. Each time you add a dose you are adding more sulfites that will permanently bind with the wine. Add too many doses and your wine may become victim of an overdose. The result is a wine that has a permanent sulfur taste.
Here’s The Good News…
It takes a significant amount of bound sulfites to detectable within the wine’s flavor. If you only add the three doses mentioned earlier, you will never have a problem with flavor – it will be will below the threshold of perception – but start adding extra doses of sulfite to your wine after each racking or while your wine is bulk aging, then your wine’s flavor could start to suffer.
If you are concerned about your wines having enough free sulfite and want to add more sulfite doses than the three mentioned above, then the best thing you can do is to test. This can be done with a simple titration kit. The most popular SO2 tester for the home wine maker is Titrets by Chemetrics. These little test ampules also need a special hand-tool to perform a test.
By taking a small wine sample you can quickly determine how much free sulfite is in your wine. By knowing this you won’t be adding more sulfites than necessary to your homemade wine whether they be bound or free.
Happy Wine Making,
Ed Kraus is a 3rd generation home brewer/winemaker and has been an owner of E. C. Kraus since 1999. He has been helping individuals make better wine and beer for over 25 years.