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potassium metabisulfite

Free SO2: When and How

Protecting your wine with free SO2

Keeping the required amount of free SO2 in your wine is one of the important post-fermentation care steps you’ll need to stay on top of. While some people decide not to add SO2 (which is a personal preference, though we at Musto Wine Grape definitely recommend keeping the proper amount of free SO2 in your wine at all times), others choose to keep their wine protected by using it diligently.

Why we add it

To keep the wine protected. KMS serves as an antimicrobial and antioxidant and as such is a very important part in keeping your wine out of harm’s way. Without it, your wine can go bad very quickly.

How to test free SO2

Aeration oxidation method, manual ripper method, Vinmetrica, Hanna titrator, titrets

Setup for “aerative oxidation” method of checking free SO2. Though time intensive, it yields exact and accurate reuslts.

When to add it

  • During crush (to kill off any unwanted native yeast)
  • When fermentation has completed (be sure that MLF has completed as well, if that’s the goal)
  • During aging. Example: Each month many winemakers will test SO2, make any SO2 adds if needed, and then top it off.

Investing in Vinmetrica SO2 wine analyzer makes testing easy

How to add it

You’ll need to get potassium metabisulfite, if you don’t already have it. You may prefer to use campden tablets, which is fine too. Make sure it says potassium metabisulfite rather than sodium metabisulfite. The easiest way to figure out how much free SO2 you’ll need to add is to know your pH, first of all. Then you’ll need to decide if you’re using .8 or .5/6 molecular SO2. .8 is usually used for white wines, whereas .5 is used for red wines. Measure your free SO2 if you have a way of doing so. Then use the graph below to figure out what the target free SO2 is. From there you will likely choose an easy-to-use online resource such as wineadds.com to find out exactly how many grams of potassium metabisulfite should be added. Mix it with a small amount of water to ensure it can become completely incorporated into the wine.

*Remember: just knowing your target free SO2 in ppm does NOT tell you how many grams you will be adding. You need to figure that out as a second step, with an online SO2 calculator*

Graph indicating required free SO2

Now that you have a solid understanding of why, how, and when you add meta, you may want to delve into some deeper questions, such as…

Why do I need to keep adding meta? If I add a certain amount shouldn’t it stay at that number?

This is a great question. There are a lot of variables that go into answering this in as cohesive a way possible, and this could really be a topic in and of itself. Let’s keep it simple here: there are two measurements of SO2 in wine: free and bound. The free SO2 is what is actively protecting the wine, whereas bound SO2 is what has already tacked on to other compounds within the wine and as such is no longer able to actively protect it in the same way. Both are important numbers, but if a winemaker is only checking one, it’s going to be free. Over time free SO2 can become bound to various acids, solids, sugars, bacteria, yeasts, etc., that are present in the wine, which is why this number will not necessarily stay constant, especially immediately.

Why does pH affect how much SO2 I need to add?

A rule of thumb to remember is that higher pH = higher free SO2 requirement. Lower pH = lower free SO2 requirement. The chart below demonstrates the amount of free SO2 required base don the pH of the wine. This is just one of the many reasons that checking and knowing your wine’s pH is critical.

Do I need to measure total SO2 as well?

Knowing this number is important, but not as crucial as knowing your free SO2. It’s also a little less accessible of a test to run, which is why most home winemakers don’t choose to pursue knowing the total SO2 of their wines. It is possible to overadd SO2 and have the total SO2 be higher than desirable which can be problematic, so be sure to keep a running log and closely track how much you have added from the beginning of the wine’s life onward.

The Winemaker’s Think Tank: Vol 5 – Is Malocatic necessary in White Wines if it has not been inoculated?

Wine expert testing wine silhouette image

What’s the Winemaker’s Think Tank? 

Every Thursday we will post about a few frequently asked questions that our winemaker has answered. If you have a winemaking question you would like to have answered, please email us at support@juicegrape.com and we will try to get into next week’s post. Cheers! 🙂

Is Malocatic necessary in White Wines if it has not been inoculated?

When considering the stability of a white wine in preparation for bottling, sugar and microbial stability are of great importance. After fermentation, if MLF is not purposefully inoculated by the winemaker, the addition of Lysozyme may be considered as to retard any naturally present MLF bacteria from beginning to ferment. If the level of SO2 is kept up to is suggested level (contingent upon pH), the Lysozyme may not be needed as the SO2 will prevent the bacteria from fermenting. If the winemaker is trying to use a low amount of sulfites in their wine, I would suggest the use of Lysozyme to inhibit any bacterial growth.

Equally as important, is the use of sterile filtration. If the wine is processed through a sterile filter (.45µ), bacterial and yeast cells should be eliminated. This will physically prevent the bacterial spoilage of the wine. If the winemaker chooses to back sweeten the wine, this filtration will also help prevent any refermentation within the bottle. When it comes to back sweetening, I also always recommend chemical as well as physical sterilization of the wine to prevent fermentation and off aromas to develop within the bottle. Potassium sorbate may be used on any wine that has not gone through malolactic fermentation. If it is used on a wine that has undergone MLF, remaining MLF bacteria can begin to metabolize the sorbate, resulting in a strong geranium odor. In my experience, I typically add sorbate and sterile filter the wine, then bottle, without the addition of Lysozyme. I am meticulous about the level of SO2 remaining above the suggested amount , and I typically add an additional 10ppm before bottling to ensure prolonged sterility within the bottle.

While you certainly can conduct a chromatography test upon the wines to detect the presence of acid, both malic and lactic exist naturally within the grape, so the chromatography test will not be especially helpful when looking at a wine that has not gone through MLF. As long as you keep a vigilant watch upon your sulfur dioxide levels and pH, and use sorbate when sweetening, you should be fine.

We hope this information helps with your winemaking. If you have any follow up questions or winemaking questions in general, please email us at support@juicegrape.com. 

The Winemaker’s Think Tank: Vol 4 – What is the best way to sanitize my equipment?

Wine expert testing wine silhouette image

What’s the Winemaker’s Think Tank? 

Every Thursday we will post about a few frequently asked questions that our winemaker has answered. If you have a winemaking question you would like to have answered, please email us at support@juicegrape.com and we will try to get into next week’s post. Cheers! 🙂

What is the best way to sanitize my equipment?

It is important to differentiate between cleaning, sanitizing, and sterilizing. Cleaning is removing any dirt, grape debris, or build-up from your equipment. Sterilizing is the process via heat or chemicals of eliminating all micro-organisms, which is nearly impossible in a home winemaking environment. Sanitizing is the goal for home winemakers. Sanitizing is the removal of harmful micro-organisms from the winemaking equipment. This will give the winemaker the healthiest environment possible for their wine. One of the most chemically and cost effective ways to sanitize winemaking equipment is by using potassium metabisulfite. Potassium metabisulfite works best in an acidic environment. To create a strong sanitizing solution, mix 2 tbsp. of citric acid and 1 tbsp. of potassium metabisulfite with 5 gallons of warm water. Mix all of these in a 6 gallon pail. You can now use this solution to sanitize all of your equipment. Submerge or rinse all of the equipment in this solution. This solution will sanitize the equipment of any harmful bacteria that could spoil the wine. Any tool, vessel, or hose that touches the wine should be rinsed thoroughly with the solution to prohibit contamination.

Also, check out our Youtube Video where our Bootcamp Professor Frank Renalid weighs in on sanitation

 

We hope this information helps with your winemaking. If you have any follow up questions or winemaking questions in general, please email us at support@juicegrape.com.