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g WINE g rAoKw i n g rape M ING A. Freeze test The most basic version of this test is to freeze a wine sample, then thaw it and look for the presence of crystals. Common variables of this test include the pretreatment of the sample (filtration compared to none); addition of KHT powder or not; sample size; freezer temperature; length of time in freezer (hours to days); thawing regime; temperature of evaluation and method of evaluation (visual compared to turbidity). Test time commonly ranges from several hours to several days, with "overnight" being a common descriptor. Freezer temperatures also vary; the sample must change state from liquid to a solid. As a rough rule of thumb, the freezing point in: ºC = -0.5 x % alcohol (v/v) (Table I). Ultra-clear wines may occasionally refuse to freeze, invalidating the test. The freeze test effectively increases the concentration product (CP) value by raising the alcohol and concentrating the potassium ion (K+) and the tartrate ion (HTa-). It induces nuclei through the increase in the CP compared to the holding capacity and kinetic limitations of the wine, to overcome the energy barrier for nuclei formation and/or use of ice crystals or scratches in the container surface for heterogeneous nucleation sites. Table 1: Estimated Approximate Freezing Temperatures of Wine Alcohol TemperatureTemperature (% of vol) (Centigrade) (Fahrenheit) 10.0% -5° 24° 12.0% -6° 23° 14.0% -7° 21° 16.0% -8° 17° Questions about the freeze test involve how to deal with crystal formation and melting, the optimization of concentration and time and the lack of control of diffusion. The extreme nature of the test—actually changing physical state— makes the predictive index hard to understand. False negatives and false positives are definite possibilities. Despite these concerns, it is a commonly used test due to its speed, low expense and ease. B. Cold-hold test (with or without inputs) This test involves chilling the wine for an extended time, then evaluating the wine for crystals. These tests differ from freeze tests (above) in that the wine does not solidify or become slushy, and the time stored cold is generally longer, from several days to several weeks (or several months in some cases). Many of the coldhold challenge tests are listed at -4ºC. However, in actual practice, the coldhold temperature will become that of the winery's laboratory refrigerator, which may or may not be properly documented. Common variations of this test include pre-treatment of the sample (filtration or not); additions of KHT powder to overcome the lack of seed in a filtered wine; different sample sizes; a wide range of refrigerator temperature and fluctuation; a variable length of time in refrigerator (days to weeks or months); different warming regimes; different temperatures of evaluation; and various methods of evaluation (visual or turbidity). The "cold-hold" test may most closely mimic, on a short time scale, the actual situation a wine must survive, if the treatment inputs are properly defined and managed. As a predictive index this imitation of potential actual condition has great appeal, but the shorter time frame can cause concern, as a falsely reassuring test could result. Cold-hold tests were used to develop many of the predictive models for faster pr actica l win ery & vin eya rd APRIL 20 13 59