Have you ever noticed after finishing a bottle of wine that on occasion there is a dark dusty-looking deposit clinging to the bottom of the bottle? Have you ever had a wine become cloudy in the bottle after it was once beautifully clear?
These are two examples of what can happen when a wine is unstable. What is meant by "unstable" is simply, there are still changes that may occur in the wine when the conditions are right.
There are many changes that occur during the production of a wine - some organic, some chemical - some good, some bad. Some are obvious such as a fermentation. Some are more subtle such as the enzymatic changes that take place during the aging process.
What Is Precipitation
One type of change that can occur in a wine that causes a lot of problems for the unsuspecting winemaker is called precipitation. Precipitation is when particles occur in a wine from out of nowhere. They are solids that are created from the liquid.
These precipitations occur over time when there is more of a substance in the wine then the wine can hold. It's no different than a cloud trying to hold more water vapor than the climatic conditions will allow. The clouds will precipitate the water in the form of rain.
Temperature is a big factor in determining if a precipitation will occur in a wine. To take our weather example a little further, the warmer the air gets the more likely the clouds will produce rain. The opposite holds true as well.
The same is true for wine, certain solids are more likely to precipitate out of the wine when it is warmed up. There are also certain solids that are more likely to precipitate out of a wine when it is cooled down.
Some wines will not precipitate anything regardless of temperature. These wines are said to be "temperature stable". But in general, most wines will precipitate something when taken to an extreme, whether it be hot or cold.
Most of the precipitation that occurs in wine is caused by from either excessive tartaric acid or excessive wine tannin. Tartaric acid is the major source of acid found in grapes. Tannin, also known as tannic acid, comes from the skins and stems of the grape as well as many other fruits.
When their concentration levels are beyond the saturation point of that particular wine, at a particular temperature, then precipitation will occur when given enough time. Quite often it will show up several months after the wine has been bottle, making a perfectly good tasting wine become visually unappealing.
TARTARIC ACID PRECIPITATION:
This type of precipitation results as small, white to beige colored flakes that will stay suspended in the wine for some time and then eventually settle to the bottom in the form of cream-of-tartar. This type of precipitation is most commonly associated with white wines.
Wines that are stored in cooler areas are more likely to produce this type of precipitation than wine stored at room temperature. But, it may occur at any time with wines that have extremely high levels of tartaric acid.
TANNIC ACID PRECIPITATION:
This type of precipitation will be seen as a dark, dusty deposit at the bottom of the wine bottle. You will find this type of precipitation almost exclusively in heavier red grape wines, such as Pinot Noir, and also in darker berry wines - elderberry being the primary candidate.
Unlike tartaric precipitation, tannic precipitation is more likely to occur when the wine is stored at a warmer temperature. But, it may also occur very slowly at cooler temperatures in wines that are extremely heavy in tannin.
The dark deposit that is created by this type of precipitation is not the tannic acid itself, but rather tannic acid that has bonded with various types of proteins in the wine - usually color pigmentation.
Temperature Stability Tests
Before getting all bent out of shape thinking your wine is going to "flake-out", there are a couple of simple tests that you can perform on a given wine to determine if it is unstable and has the potential for precipitation.
-The first test is the "cold stable test". Take a small portion of the wine, say about 1 cup, and freeze it. After it has frozen solid, then allow it to thaw. If you see an abundance of creamy looking flakes, then your wine is not cold stable.shop-bentonite.png
-The second test is the "heat stable test". Take a small portion of the wine and bring it to just short of boiling then allow it to cool down for a few hours. If you see an abundance of dark dusty looking precipitation, then your wine in not heat stable.
Now realize, that a little bit of precipitation in either one of these tests is okay. We are taking the wine to both extremes - temperatures they will never actually encounter during storage, so a little bit of precipitation is acceptable.
Also, it is important to note that these tests should only be performed on wines that have been given an abundance of time to settle out the wine yeast and fiber particles from the fermentation. Otherwise, you will get these items depositing as well, making it hard to determine these tests' results.
What Can You Do About It?
It is important to note here that filtering wine has no effect on whether a wine will precipitate or not. A beautifully filtered wine can become cloudy or with ugly deposits just the same as an unfiltered wine. So filtration is not the answer to this type of problem. However, there are a couple of things you can do to help eliminate the chance of these deposits from occurring in your bottles.
COLD STABLE TREATMENT:
If you have determined that your wine is not cold stable, then you should treat it by cooling the entire batch down to 35 to 45 degrees Fahrenheit for 1 to 2 weeks before bottling. The idea here is to cause all of the excess tartaric acid to precipitate out now, so that it will not occur later in the bottles.
To help trigger the precipitation, it is recommended that you add 1/4 teaspoon of cream-of-tartar crystals for each gallon of wine. This is the same cream-of-tartar you will find in the spice section of your local grocery store.
To speed up the process, gently stir the wine once a day or on occasion to keep the flakes suspended, so that they may attract more precipitation.shop-wine-tannin.png
HEAT STABLE TREATMENT:
The most effective way to heat stabilize a wine is to heat it up. Unfortunately, this is not a practical solution because of the other effects heat has on wine such as oxidation and denaturing. If you have determined that your wine is not heat stable, the best coarse of action is to treat it with a full dose of Bentonite. Bentonite is a wine clarifying agent that is regularly used by wineries. Not only does it effectively clarify particles that may be linger from a fermentation, it also has the ability to induce protein precipitation, which is what tannic acid would eventually cause on its own if left untreated.
To help trigger the precipitation, it is recommended that you add 1/4 teaspoon of wine tannin for each gallon of wine. This should be done at least a few hours before the Bentonite treatment is performed.
"Using Bentonite As A Wine Clarifier"
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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.