Chapter 10

Tartrate Stabilization of Wine

Measurement of Cold Stability of Wine

An analytical test should precede cold stabilization and repeated following cold stabilization to verify the process. There are several analytical options available for evaluating cold stability. The three most commonly used methods are visual, concentration product, and conductivity. Results of both these cold stability methods should be used as guidelines, as they are not indicative of absolute cold stability due to the complex variability of colloidal interactions.

Three-Day Freeze Test

This test is the preferred method for assessing cold stability and is the industry standard. Samples are kept at -4 degrees C (25°F) for 3 days and then visually inspected for the presence or absence of crystals.

Freeze/Thaw Test

The freeze/thaw test is a visual test for the detection of crystal formation. The freeze test involves freezing a wine sample until it is the consistency of a slushy. The freeze test effectively increases the concentration product (CP) value by raising the alcohol and concentrating the potassium ion (K+) and the tartrate ion (T2-). Test time commonly ranges from several hours to several days, with overnight being a common descriptor.

Modified Mini Contact (UC Davis) Conductivity Test

The conductivity test is a far more accurate means of predicting cold stability, and involves seeding the wine sample with finely ground KHT crystals. This test is run at a specified temperature over a 30-minute time period. If the change in conductivity of the sample is 5 percent or more (due to precipitation of KHT and a resulting decrease in conductivity), the sample is considered to be unstable with respect to KHT. When conductivity drops by less than 5 percent over the test period, the wine is generally considered stable, although wineries often use a more stringent criterion of 3 percent (Hornsey, 2007).

Potassium Concentration Product Test

The Potassium Concentration Product (KCP) method estimates the relative KHT stability of wine at a given temperature and is used as an indicator of the potential formation of KHT. The pH and the ethanol content of the wine determine the percent of tartrate in the bitartrate ion (HT-) form. The concentration of bitartrate (HT-) and potassium (K+) are used to calculate the KCP. This number is expressed using exponents: KCP x 10-5.

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