Mini-contact test

The mini-contact test is based on homogeneous induced nucleation, which is faster than primary nucleation. However, this test does not take into account the particle size of the seed tartrate, although the importance of its effect on the crystallization rate is well known. The operative factor in this test is the surface area of the liquid/solid contact interface. Furthermore, this test defines the stability of the wine at 0°C and in its colloidal state at the time of testing. In other words, it makes no allowance for colloidal reorganization in wine, especially red wine, during aging. 

It should be noted that mini-contact test results tend to overestimate a wine s stability and therefore the effectiveness of prior treatment. This statement is based on work by Boulton (1982). After 2 hours contact, only 60-70% of the endogeneous tartrate has crystallized and therefore the increase in weight of the crystal precipitate is minimized. These results are interpreted to mean that the treatment was more effective, or the wine more stable, than was actually the case. In order to make the mini-contact test faster, more reliable and compatible with the dynamic contact process, the Martin Vialatte Company proposed the following variant in 1984 seeding a wine sample with 10 g/1 of cream of tartar and measuring the drop in conductivity at 0°C. 

As this test is based on measuring the wine s electrical conductivity, it has the tremendous advantage that there is no need to collect the precipitate by filtration and determine the increase in weight. This new mini-contact test, measuring conductivity, is much faster (5-10 min instead of 2 h). Furthermore, by comparison with the first variant of the mini-contact test, as the contact surface (A) and, consequently, the state of supersaturation of the wine are multiplied by 2.5 (adding 10 g/1 of KTH instead of 4 g/1), it gives a more accurate assessment of a wine s stability. 

Table 1.13. Values of the concentration products of wines and the corresponding percentage drop in conductivity produced by the mini-contact test...

Table 1.14. Demonstrating the limitations of the reliability of the mini-contact test in assessing the stability of a wine by adding increasing quantities of potassium bitartrate and measuring the percentage drop in conductivity...

Table 1.15. Influence of tartrate particle size and mini-contact test time on the percentage drop in conductivity of the wine...

Figures 26.9(a) and (b) show how laboratory techniques can assist in the apphcation of GAC for the removal of geosmin and MIB. Figure 26.9(a) shows the results of a mini-column test on GAC removed at various intervals from a GAC pilot plant [17]. The percent removal of MIB was measured in the laboratory by running a mini-column test at the same empty bed contact time as that used in the pilot. Further details can be found in [68]. The results indicate that GAC filters could be tested at regular intervals for the removal of MIB using a simple laboratory trial. Figure 26.9(b) compares the experimental data points obtained during a SBA test with the HSDM fit and predictions [68]. The carbon had been preloaded for 2 years in a pilot plant. The predictions and the...

Certain aspects of the operation of mini-fuel cells with a large contact surface area between cathode and ambient air were examined by Schmitz et al. (2004) for a methanol-air mini-fuel cell. They studied the elimination of product water when the open contact surface area was in different spatial orientations pointing up horizontally, and vertical. The tests were conducted while ambient temperature varied between 25 and 31°C. It was found that cell operation was more stable with a vertical orientation of the contact surface area. In this orientation, the values of relative humidity at points close to the contact surface area were lower than in the horizontal orientation. As an explanation, the authors suggested that the water vapor produced will partially condense, yielding liquid droplets, which, under the effect of gravity, will slip down the vertical surface. 

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