Issue link: http://winesandvines.uberflip.com/i/116287
g WINE g rAoKw i n g rape M ING tests. Cold-hold, with and without seeding, and held for extended time periods (months) at various temperatures, was used as the method to obtain the concentration product and the degree of saturation models. Three days at -4ºC (24.8ºF) cold-hold was used in modeling the "DIT" test, while six days at -4ºC cold-hold was used in forming the "ISTC-50" tests. Conductivity tests have had only limited success in determining the calcium tartrate stability primarily due to the lack of effective nucleation. As currently used, most of these tests make few claims on being effective calcium tartrate stability predictors. Lab Testing Category II: Conductivity methods This test measures the change in conductivity over time of a chilled, mixed and heavily super-saturated (using powdered KHT "spiked" into the sample) wines. Common operator-chosen variables include test temperature; quality, mesh size, and amount of seeding tartrate powder; time of running the test; and acceptable conductivity change (either in percentage or absolute values). Equipment variables include the ability to hold the selected temperature during the test, mixing intensity and speed, and choice of meter and probe sensitivity and ruggedness. All of these variables may impact the test. The published method specifies to run the test until two or three consecutive measurements are the same (usually less than 30 minutes). The perceived simplicity of the test has been the major source of mis-application. This general category of test uses the conductivity method as an indirect measure of potassium ions; conductivity can follow the change in potassium concentration in the sample during treatment. Conductivity is used rather than primary potassium analysis because is it rapid, relatively inexpensive and can be monitored "real time" during the test. Conductivity can be affected by fluctuations of hydrogen ion concentration (changes in pH) or uncontrolled changes in temperature. Use of potassium testing to confirm conductivity results is limited by the current precision of potassium measurements (although this is changing rapidly), but could certainly be used as a research or confirmation tool when conductivity may be affected by these factors. 60 p racti c al w i ne ry & v i n e yard APRIL 20 13 A. "Mini Contact" Conductivity Test, Variation I: "UC Davis Conductivity Test" There is tremendous variation in the quality of the equipment and the ability to control or document the critical test parameters, resulting in poor method performance. The scientific appeal of this test is that it removes the kinetic limitations and, by choosing the temperature appropriately near the lowest expected temperature the wine is to experience, models it to that situation. Recent commercialization of the cooling/mixing/conductivity system by both French (the "Stabilab" available from Oenodia) and Italian (the "Checkstab" available through Alpine Scientific) equipment manufacturers have introduced more precision into temperature control, conductivity measurement and time recording as it applies to the application of this test method. These (and other) brands of instruments are capable of running various versions of conductivity testing. Most can run the "Davis" test with much better overall control, and may result in improved performance while still offering the advantages of the method. B. "Mini Contact" Conductivity Test, Variation II: "Degree of Tartrate Instability" (DIT) This test measures the change in conductivity over time of a chilled, mixed