Tuesday, August 16, 2011

The Ice Age is Over

If there is one machine that will truly make my life easier, it is the electrodialysis filter that will soon be showing up on our loading dock. This filter eliminates the cold stabilization process currently used to prepare wine for bottling. In large production facilities, it is essential to cold stabilize wine. Cold stabilization refers to the process of removing excess tartaric acid as its salt, potassium hydrogen tartrate (KHT). The acid crystal is considered undesirable in young wines by American consumers, and we make quite an effort to ensure the chance of them forming in a young bottled wine is removed.

At wine pH, most acids will be at least partially deprotonated. In other words, they will exchange a hydrogen with a molecule of water and temporarily be left with a negative charge. This process happens countless times per second, but averaged over time the negative charge is available for reaction. When a potassium ion, which is positively charged, meets the negative charge on the tartrate, a stable ionic bond is formed and the molecule precipitates (becomes solid). This happens naturally with aging, but there are ways to accelerate the process. The usual way takes advantage of solubility.

Temperature greatly affects solubility. As temperature falls, so does solubility. Temperature is related to molecular vibration, more simply the space created between molecules by like-charge repulsion. The majority of molecules in wine are water molecules, as they are cooled their vibration slows and they move closer together. This literally squeezes out molecules which are unable to fit between the lattice. Modern wineries use a glycol cooling system to lower wines below the freezing point of water and precipitate out KHT molecules to settle at the bottom of the tank. If they do not perform cold stability and bottle soon after harvest, tartaric acid crytals will appear in the wine bottle. Additionally, we add an excess of KHT to the tank once it has cooled to provide a substrate for additional KHT precipitation. The process takes somewhere around two weeks to a month, during which time thick ice coats form on the jackets used to cool the tank.

Once cold stability is confirmed through a lab conductivity test, the wine is ready for filtration. It cannot be allowed to warm before filtration or the KHT crystals will dissolve back into solution. Our method of choice is a crossflow filter. At 8 gallons per minute it can be quite a process to filter just our Pinot Noir, and during the summer it is taxing to chill large tanks to the necessary temperature. That is why I am so excited for our new technology.

ED filtering is not new, but it is still very expensive to get started. However, the savings start paying for it immediately. Electrodialysis filters use an electric charge coupled with ion selective filters to attract potassium ions out of the wine. By removing excess potassium ions and some tartaric acid ions, the wine not longer has the chemical potential to precipitate tartrates in the short term. It is inevitable that it will happen eventually, but the amount is usually small and at that point, desired by the consumer as a show of maturity.

The filter does not require the wine to be cooled, making it a huge power saver. The crossflow filter can be run at cellar temperature as well, which speeds it from 50-100%. The filter also allows us to cut down the time required to prepare a wine for bottling. At the speed we are expanding every second counts. To me, this machine made absolute sense as a purchase. It saves us money, time, lab analysis, and me getting hit in the head by falling ice jackets. Oh, and I might just sleep a little better this year too.


  1. I know very little about chemistry, and less about wine, but I find this blog fascinating! Keep up the good writing. I look forward to learning more from you about wine, my home state of Oregon, and getting a little chemistry refresher!

  2. So does this mean more and more overly sweet, highly alcoholic, one note wines? We've almost given up on American wines, and we used to be big fans.

  3. @Kale -
    I'm glad you brought this up it is a perfect post to write....I will get it up today