Wine Making: Vinegar in Wine
There's something about the wine you're drinking that may surprise you. There's vinegar in it.
It doesn't matter if you made the wine using fruits from your own backyard or from pre-packaged juices like we offer. It doesn't even matter if you made the wine yourself or picked up a bottle from the local liquor store. There's vinegar in it.
In fact, vinegar is an integral part of wine. That is to say if a wine contained absolutely "zero" vinegar it would tasteless eventful, lacking of character and out of balance. There have even been some wineries that have been known to encourage a minimal amount of vinegar production to enhance the character of their wine in a controlled and subtle way. This may all sound absolutely weird to you, but the fact is that the natural process of making wine lends itself the production of some vinegar. There's simply no way around it. Here's why...
Why Is Vinegar In Wine?
Vinegar is the result of a process. Much like sugar is converted into alcohol during a fermentation, alcohol can be converted on into vinegar. Veteran winemakers refer to this vinegar as "acetic acid"--one of the many types of "volatile acids" that can occur in a wine.
Much of the vinegar that may be in a wine is produced by a bacteria known as acetobacter. This microorganism is naturally everywhere: on the skin of the grape; floating in the air; on your wine making equipment. This acetobacter consumes the alcohol and creates acetic acid (vinegar).
But what many home winemakers do not realize is that vinegar is also produced by the yeast as well. That's right. The yeast also takes a fraction of the sugars available to them and reduce them on down to acetic acid during fermentation. So, if your goal is to make a wine that is *vinegar free*, your efforts will be ultimately futile.
What's The Point Of Telling You This?
The point to all of this is to help you understand that vinegar plays a definite and acceptable role in the make-up of any wine, whether it be a Grenache Rose from the local liquor store or blackberry wine from your own backyard. It is not something to be feared but rather something to be understood and managed.
Your role in all of this, as a winemaker, is to limit the production of vinegar. Keep it to a reasonable level, one that is in harmony with the wine. If the acetobacter is left to its own natural coarse, then yes, you will eventually end up with a batch of full-fledge vinegar ready for your next salad. But, with a little bit of understanding you can limit the vinegar production to a reasonable amount with minimal effort.
Putting Vinegar In Perspective
The production of vinegar and other volatile acids in a wine is considered undetectable at levels of .05% or less by volume. And, it is considered acceptable in concentrations as high as .10% by volume. California, for example, has put limits on volatile acid volume at .10% for whites and .12% for reds. Australian wines are allowed to have up to .15% by volume.
Domesticated wine yeast will produce volatile acids--mostly vinegar--in the range of .02% to .06%, depending on the conditions of the fermentation. Warmer, faster fermentations tend to produce more volatile acids than cooler, slower fermentations. Wild yeasts will produce much higher levels of volatile acid.
The vinegar is usually noticeable as an odor coming from the wine before it is noticeable as a flavor within the wine. The odor is what one could described as fingernail polish.
Many novice winemakers mistake the flavors and bouquet of a dry wine as being that of vinegar. One must be careful when assuming their wine is turning to vinegar. Quite often it is only a case of the winemaker not liking drier wines. This type of problem can easily be solved by making a final adjustment to the sweetness of the wine and then adding a wine stabilizer to prevent the occurrence of re-fermentation.
How To Control Vinegar Production
There's not much you can do to control vinegar production during fermentation other than to keep the fermentation temperature below 75 degrees F., as mentioned earlier. Doing so will keep the volatile acid production done by the yeast well below acceptable levels.
It is acetobacter that we must primarily concern ourselves with when we talk about controlling the volatile acids in a wine. During the fermentation the acetobacter is not able to produce vinegar to any relevant degree. This is because of the inhibiting effects CO2 gas has on acetobacter--assuming you have a vigorous, healthy fermentation. But, once the fermentation has ended and the protective CO2 gases are no longer being produced, it is then time for measures to be taken that will help to control the acetobacter.
It is important to understand that the production of vinegar is an oxidative process. In other words it takes oxygen to produce vinegar. Without oxygen the acetobacter poses little threat. So, the key to keeping vinegar production to an acceptable level is to keep the oxygen away from, and out of, the wine.
1. There are two basic ways of accomplishing this task:
The first way to reduce the oxygen made available to the acetobacter is to store the wine in a container that has next to no head-space.
During the fermentation the head-space is of little consequence. Even fairly large head-spaces are of little issue while an active fermentation is present. This is because the head-space is being filled with protective CO2 gas from the fermentation during this time, but after the fermentation has completed and the container has been opened and exposed, then head-space does become an issue.
After the fermentation has completed you will want to either move the wine to a more appropriate-sized container that will provide little head-space or you will want to top-up the container that the wine is currently in. For more information about this you may want to take a look at the article, "Topping Up Your Wines".
2. The second way to reduce the amount of oxygen that is available to the acetobacter is to use sulfites. This would be items such as: Campden Tablets, Sodium Bisulfite and Potassium Bisulfite. Any of these items will be effective in not only controlling the amount of oxygen available to the acetobacter, but they are also effective in destroying the bulk of its existence.
It is important to note here that you should not use sulfites during a fermentation as this will interfere with the performance of the yeast just like it does the acetobacter.
Fixed Acids Vs. Volatile Acids
There are two major categories of acids in a wine: "fixed acids" and "volatile acids".
Fixed acids are acids such as citric acid, tartaric acid or malic acid. All three make up Acid Blend, commonly used in wine recipes. Other examples of fixed acids would be the tannic acid found in Wine Tannin; or, the Ascorbic Acid used in some wines to preserve flavor and color.
These acids are called fixed acids because they are stable within the wine when stored under normal conditions. As the wine sits the level of these acids do not change. They are "fixed."
On the other hand, volatile acids such as vinegar are not stable. If a wine sits open at normal temperatures, vinegar along with other volatile acids will slowly dissipate from the wine. And, at warmer temperatures they can dissipate fairly rapidly. This is one of the reasons that vinegar effects the bouquet of a wine so easily. What you are smelling is the vinegar as it slowly dissipates from the wine.
It is this difference between fixed acids and volatile acids that allows the home winemaker to do their own test for volatile acidity in their homemade wines.
How To Test For Vinegar In Your Wine
Professional wineries will test the volatile acidity (vinegar) by distilling it off of the wine to obtain a measurement. This method is somewhat accurate but hardly practical for the home winemaker. The large wineries will resort to chromatography analysis. It is very accurate, but very expensive. Again, making it impractical for the home winemaker as well. But there is another method that is much easier to perform, however it is not quite as accurate. Having said this, it is accurate enough for the average home winemaker's needs. It involves comparing two acid level readings taken with an Acid Test Kit.
The Acid Test Kit will give you the percentage of acid in a given wine by volume. For example, a typical reading might be .65%. This percentage includes both fixed and volatile acids. If one were to boil the volatile acids off of the wine and take another reading, they might get .60%, or maybe .55%, depending on how much volatile acid was in the wine. By comparing the second reading with the first then you can determine the level of volatile acids (mostly vinegar) that is in your wine.
To take the above example further, in the case of a second reading being .60% this would means that your wine has a volatile acid level of .05% (.65% less .60%). If you ended up with a reading of .55% then in this example your wine would have a volatile acid level of .10%(.65% less .55%).
The boiling process needs to be done with some care. First, the sample of wine you use should be accurately measured. Starting with an even pint or cup as a sample is reasonable depending on the size of sauce pan you have available.
Boil the wine until it is roughly 1/3 its original volume. Add boiling water--distilled preferably--to the wine to bring it back close to its original volume. And, then allow it to boil down to 1/3 its original volume, again. Repeat this process for a third time.
Once you have completed the boiling process and the sample has had time to cool to room temperature, it may be necessary to do a final adjustment with more distilled water before taking your second reading. It is very important that the sample ends up being the exact same volume as when you started. Remember, accuracy is important here.
The last step is to take your second reading with the Acid Test Kit and compare that reading with the one you took of the sample of wine that was not boiled, and you are done.
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