WINETECH Technical Yearbook 2021

of which are determined by pH. With increasing pH, the H 2 T-percentage decreases, the T -2 -percentage increases and the HT-percentage increases initially to a maximum at a pH of 3.6 to 3.7, whereafter it decreases again. The concentration product (CPK HT ) is calculated by the following formula: CP KHT = (K (mg/L) ÷ 39 100) x (tartaric acid (g/L) ÷ 150.1) x (% bitartrate ion ÷ 100). Concentration products differ at different temperatures and wine types (www.etslabs. com). Researchers also differ concerning the marginal stability value for wine. For white wine it is 8.0 to 9.4 x 10 -5 and red wines 17.6 to 18.0 x 10 -5 . If it is lower than these values, the wine is seen as stable.

This method however requires advanced analyses executed by wine laboratories. All the mentioned stability tests have a degree of uncertainty and also cannot indicate future stability. This is not necessarily due to the test method, but rather as a result of changes in the wine composition over time. A conductivity test, which can determine the saturation point (TSAT) at different temperatures, can determine the status of a wine’s cold stability (Carey, 2021). REFERENCE Carey, R., 2021. Cold stabilization testing has many options. Wine Business Monthly , May 2021: 26-33.

at room temperature the wine is shaken. If the crystals are then dissolved the wine is seen as stable, but if it is not dissolved it is seen as unstable. The disadvantage of this test is the reliance on visual appearance. If the crystals do exist, but are invisible, a wrong conclusion will be made. With the cooling test a wine sample is kept at -4°C for three days. If crystals do appear then, but dissolve again at room temperature, or no crystals appear after cooling, the wine is seen as stable. The conductivity test uses the conductivity of wine at a certain temperature to deter- mine its cold stability. The conductivity of wine is influenced by temperature and at lower temperatures the conductivity is low- er. After the wine is cooled to the required

temperature of 0°C for white or 5°C for red wine, up to 4 g/L of potassium bitartrate is added to it and stirred for 30 minutes. If the wine has already been cold stabilised in any way, the dosage of potassium bitar- trate can be diminished. If the conductivity does not decrease more than 4% when the required temperature is reached, the wine is seen as cold stable. The calculation of the concentration product of potassium bitartrate (CP KHT ) is a more complex way of testing cold stability. Tartrate instability is determined by the temperature, pH, tartrate concentration and the composition of the tartrate concentration. The latter consists of tartaric acid (H 2 T), bitartrate ions (HT - ) and tartrate ions (T -2 ), the percentages

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