Abstract
The saturation temperature of potassium hydrogen tartrate (KHT) in port wines was experimentally determined by conductivity measurements as a function of temperature. Based on different fittings of these experimental values, a new method is proposed to predict the tartrate stability of commercial port wines, avoiding a time-consuming experimental procedure. The linear fitting tested for both curves (with and without crystals) may explain why the Würdig equation is commonly used to estimate saturation temperature. However, the quadratic/ exponential approach also evaluated enables a better estimation of saturation temperature, as a good agreement with the experimental values was obtained (σ = 0.7°C), in the range of 15 to 35°C.
- Tsat: temperature of saturation (°C)
- KHT: potassium hydrogen tartrate
- T: temperature (°C)
- C: conductivity (μS·cm−1)
- A-type: conductivity measurement of wine without KHT addition
- B-type: conductivity measurement of wine with 4.0 g/L KHT addition
- ΔC: conductivity difference (B- and A-type measurement) at a given temperature (μS cm−1)
- K: slope of a given conductivity curve (dC/dT, μS·cm−1·°C−1)
- n: order of derivative
- P1: null order coefficient used in the estimation of dnC/dTn
- P2: first-order coefficient used in the estimation of dnC/dTn
- Tref: temperature at which conductivity measurements are made, or at which derivatives are calculated (°C)
- Q1: first parameter of Würdig equation (°C)
- Q2: second parameter of Würdig equation (μS·cm−1·°C−1)
- a1: second-order coefficient for description of conductivity as a function of temperature (quadratic approximation, μS·cm−1·°C−2)
- b1: first-order coefficient for description of conductivity as a function of temperature (quadratic approximation, μS·m−1·°C−1)
- c1: null order coefficient for description of conductivity as a function of temperature (quadratic approximation, μS·cm−1)
- a2: preexponential term used in the approximation of the conductivity as a function of temperature (exponential approximation, μS·cm−1)
- b2: exponential term used in the approximation of conductivity as a function of temperature (exponential approximation, °C−1)
- D: slope calculated for B-type curves (μS·cm−1·°C−1)
- σ : standard deviation
- f: general function for conductivity
- g: general function for conductivity derivatives
- ε: error in conductivity measurement (μS·cm−1).
- Received December 2004.
- Revision received March 2005.
- Copyright © 2005 by the American Society for Enology and Viticulture
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Vol 56 Issue 3
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