By: Tom Payette, Winemaking Consultant
Potassium Bitartrate Stabilization
During the winemaking process and before bottling, there may be instability with a juice or wine termed Tartrate Stability or Tartrate Instability. Unknowing customers often view these crystals as a fault and are therefore unsure of whether or not to consume the wine. Once a customer is turned off by sediment, such as a tartrate precipitate, it may be difficult to get them to return to your label. An in depth discussion below is to help winemakers achieve desired results in their cellars not undesired results in their bottled wine! Winemakers are encouraged to make sure wines are bottled that will be sediment free.
Tartrates are, very simply, a chemical salt made when potassium and tartaric acid combine making cream of tarter. This cream of tarter [Potassium Bitatrtate] is harmless and is used, in the refined form, to cook meringues. When most grapes arrive on the crush pad there is often a significant quantity of tartaric acid and potassium available in the grapes to result in instability. Furthering the complication is the fact that the crystals are encouraged out of solution, forming further precipitation, in the presence of alcohol. The fact that the winemakers have completed a successful fermentation will only force more of the crystals to precipitate. The processes to remove these crystals are largely a time temperature relationship. Over time, and at low temperatures, most to all of the tartrates will form and fall out of solution.
3.65 pH Bifurcation *
A very interesting phenomenon does exist with tartrate stabilization in wine made from grapes that all winemakers should understand. (This may not apply to fruit wines) For a wine above a pH of 3.65, one should expect the pH to rise as tartrates form and fall out of solution. For a wine below a pH of 3.65, the pH will drop to a lower pH value. The shift, of the pH, is usually about 0.06 pH units but it can go as high as 0.19 pH units. This knowledge can be used, factored into and forecasted by the winemakers’ ultimate plans for a certain wine’s final pH.
Tartaric acid and pH relationship
Noting the example above, one must understand another relationship. In both examples, whether the pH rises or lowers during tartrate stabilization, the tartaric acid level will decrease in the wine as it has formed in a salt and precipitated. The tartaric acid has formed with potassium and become insoluble at that temperature during that time. If the wine were to warm, however, the salt could re-soluablize negating the above statement.
Temperature and Potassium Bitartrate Formation
As noted previously, the precipitation is largely influenced by a time temperature relationship. Wine allowed to store over long periods of time will most likely achieve stability and it can be bottled. With the advancement of sophisticated chilling systems in the wine industry, another process can be used. Wines were often chilled for two to three weeks at 27 degrees F and allowed to drop their tartrates during this time. This process was often successful but it did have its failures due to complexing agents that prevented the tartrates from forming.
Perhaps contact seeding is more widely used today especially with wines that are blended late in the winemaking process or for getting younger wines ready for bottling sooner. This process rarely fails and it does allow acid additions to be made even hours prior to using this process. Some winemakers claim this action can be intrusive and beyond gentle processing; yet, others would have it no other way.
For those interesting in contact seeding, a procedure follows. One must have an adequate chilling system, mixer, tanks that have little temperature stratification and a filtration system that can filter reasonably rapidly. A properly sized plate and frame filter is sufficient for most winemakers while using a pore size pad of roughly 7 microns. It is assumed the wine is clean enough to go through the filter pads without clogging and at a rate that will not allow the wine to warm too much potentially redisolving the tartrates previously formed during the filtration process. It is best to always check a wine first to make sure the wine is unstable before proceeding with this process. One may be able to eliminate this process if the wine is already stable.
1.Chill the wine in need of stabilization to approximately 27 degrees F or potentially lower if the alcohol level is high enough and if greater stability is desired. The wine will be stable at the seeding temperature of the wine at seeding so this temperature reduction step is critical. (In the unusual case that the wine is below 8% alcohol, one would not want to chill the wine this cold.)
2.Start to mix the wine with a Guth or Keisel style tank mixer after the desired temperature has been reached. Wait until the wine is thoroughly mixed and then double check that the desired wine temperature has been achieved and holding. (Mixing may be done in a non-splashing pump over fashion with a pump, or two, that does not bleed any air into the system)
3.Weigh 3.0 (three) grams of Potassium bitartrate for every liter of wine in the tank. Example: for a 5000 liter batch of wine we would weight out 15000 grams of potassium bitartrate or 33.0 pounds.
4.Mix this amount of cream of tartar in water or wine before adding it to the tank. (This step may be avoided but make sure no clumps exist in the cream of tarter and understand a larger quantity of oxygen may go into the wine if the substance is added dry)
5.Add the cream of tartar mixture to the chilled wine while mixing and mix for 3.0 hours or longer. Make sure all the cream of tartar stays in solution and settling does not occur. Make sure the temperature has remained at the desired level, as well, during this process.
6.After the 3.0 hours, mixing may stop but the chilling must remain on and continue to hold the desired temperature.
7.Allow the wine to settle overnight, or longer, if keeping the wine cold is not a concern. [Recent research has shown an additional three days at 27.0 degrees F will improve the final conductivity results favorably on the wines.] The wine could remain in contact with the seed for months as long as the temperature of the wine is not allowed to rise. After the overnight settling period and when filtration is desired.
8.Vent the tank and start from the racking valve filtering on coarse filter pads making sure the filtration will go rapidly. (One may want to remove any sediment “plug” first out of the racking valve by purging into a bucket before starting filtration.)
9.Continue to filter very cold into a clean, tartrate free, receiving tank.
10.Filter down under the manway door to the bottom of the tank as any filtration would be performed making sure to get all of the wine possible out of the tank. Leave the solids behind.
11.If using water to push the wine through the filtration system keep in mind these crystals are water-soluble. Make certain to use cold water and very limited amounts to not redissolve the cream of tartar making the wine unstable once again. Do not dilute the wine with the water. Perhaps consider using CO2 or nitrogen as well.
12.It is recommended to purge or sparge the receiving wine tank with Carbon Dioxide and the tank headspace of the wine tank being filtered during this process to eliminate or reduce the potential for oxygen uptake. Other gases may be used such as nitrogen or argon. (Keep in mind the principal that gases are more easily dissolved into a cold liquid solution during this step.)
13.Once the filtration is finished one may allow the tank of wine to warm and a representative sample of the tank’s contents may be taken to test that the cold stabilization action was successful and completed as desired.
14.Always double check the stability of the wine just prior to bottling and remember if more tartaric acid were added – the wine may become unstable once again.
Time / Energy / Quality
The above process works very well to achieve cold stability. The cream of tartar needed does have a cost factor yet the payback may be in the limited cooling cost for shorter periods of time during this process. Others argue this process is damaging to the wine and it is over production on wine to support chilling a tank for 14 days or more. This process will often work, yet the longer a winemaker stores a wine at cold temperatures – the more chance that the same wine will take in more dissolved gases. This greatly increases the chance for oxygen uptake and potential oxidative reactions with that wine causes further damage. Much of the above is determined by how each winemaker handles his or her wine and each factor should be considered.
Calcium Tartrate Stability Unaffected
The reader should keep in mind that the process of cold stabilization in this manner does not necessarily affect calcium tartrate stability and many of the lab tests to check stability will not measure this form of instability either.
The winemaker must keep in mind that wines blended after cold stabilization must be reestablished or at least checked to determine their stability. Two cold stable wines blended together will not always result in a cold stable wine and most often will reveal an unstable wine due to the chemistries of each wine and their resulting blend. This may even be true with same blends cold stabilized separately.
Make sure when purchasing the seed that it comes from a company that is aware of your use. The cream of tartar seed size needs to be small enough to make sure the crystals have the proper surface for the seeding to be effective. The seed particle size is best at 35 micrometers. This will give the fastest rate of precipitation and growth. A mix between 30 and 140 micrometers will do fine for this operation and is most likely the size mixture found commercially.
One may re-use the seed from tank to tank using on whites first and then on reds. If the seed is used in conjunction with bentonite, after cold stabilization has been achieved, then the seed must be retired. This re-use of the seed may greatly drive down the cost of the seed per gallon as one moves it from tank to tank. [The author has used one set of seed for over 40,000 gallons (8 – 5000 gallon tanks) of wine with success and has not experienced a failure of the process] Cross-contamination is less of an issue at this time because the wines are generally moving toward filtration and bottling in stainless steel tanks or equivalent for sanitation purposes.
Ion exchange and cross-flow filtration are rapidly approaching our industry. These processes can be used to obtain cold stability should your winery have the technology and equipment to do so.
In step three above the author has had success reducing this amount to 2 grams per liter as long as the wine is clean, chilled properly and at a desired cold temperature.
Common sense tells us that if we can do this process in the winery, during colder winter temperatures, our chilling systems will be more effective and the cellar temperature will be more conducive to the complete process. This applies to the filtration and making sure the wine does not warm too much during filtration.
Be careful when rinsing the tank after filtration. Ice may fall!
This is just one method of achieving cold stability for a winemaker working with grape based wines. Other ways are successful and may achieve the same results just as well. Each winemaker is encouraged to try the process that works best for them and their particular cellars. This process does have the quality of shorter chilling time and reduced utility bills plus faster turn around time for a specific wine – should those goals be desired. Recall non grape fruit based wines may perform differently.
* The 3.65 Bifurcation term was not located in any research literature by the author and it is a term the author has used to describe this phenomenon in his cellar work.
Tom Payette, Winemaking Consultant, has over 30 years’ experience with winery start-ups and assisting wineries already established in the industry.