Application of membrane filtration technology in the production of low alcohol wine

The membrane treatment method was combined with the method of stopping alcohol production. Hollow fiber ultrafiltration membrane was used in the late stage of yeast fermentation to remove the excess yeast cells and reduce the amount of alcohol produced by yeast, so as to prepare low alcohol wine. It can maintain the original taste and various functional components of wine to the greatest extent, and the production cost is low, easy to operate.

Test method

Record the hours and flow rate of tartar removal by dead-end filtration (taking diatomite filtration as an example), and the hours and flux of tartar removal by membrane separation, and make a flow-time curve (membrane flux) to compare the filtration performance of the two, as shown in Figure 2 and 2. The main physical and chemical indexes of wine should be detected by referring to the wine industry manual; Sensory evaluation test of wine quality changes using triangular tasting method

Membrane component selection

With the increase of ultrafiltration time, the membrane flux decreased gradually, but the rate of change was different. In the first few minutes, the membrane flux decreases rapidly. This is because at the beginning of ultrafiltration, the gel layer thickens continuously and the concentration polarization increases continuously, resulting in a rapid increase in resistance and a substantial decrease in membrane flux. After 20min of ultrafiltration, the decrease amplitude of membrane flux decreased and gradually became stable, which was because a stable boundary layer was established on the membrane surface and the adsorption effect was observed

Tends to be saturated so that the membrane flux is relatively stable; When the ultrafiltration time approached 2h, the membrane flux showed a slow decline. This was because with the progress of ultrafiltration, the sample concentration ratio increased and macromolecular substances continued to be deposited, resulting in the worsening of membrane surface pollution, which further reduced the membrane flux. Two kinds of ultrafiltration membranes with different molecular weight showed the same change rule during ultrafiltration. Therefore, during the test, ultrafiltration was performed for 20min to stabilize membrane permeability, and then ultrafiltration was recirculated for 60min to 100min.

Cleaning and regeneration capacity of filter membrane

The regeneration ability of filter membrane is an important performance of membrane materials, which reflects the reuse ability and economic performance of membrane materials, and directly affects the promotion and application of membrane. It was found in the experiment that the flux of CMF filter membrane was basically restored to the original level after simple hot water cleaning. However, the overall filtration performance was improved due to the deep cleaning of the filter membrane after hot alkali cleaning, especially the performance in the middle stage of filtration was significantly improved. The experimental results show that CMF membrane material has good cleaning and regeneration ability, and also indicates that the pollution of the membrane is mainly concentrated on the surface of the membrane, without embedding into the membrane hole, and the deposition of pollutants may be loose and easy to remove.

In microporous filtration, the initial filtration pressure is a very important process parameter. If the pressure is too large, the radial force will weaken the effect of shear force, reduce the mass transfer coefficient (K), accelerate the concentration polarization of the membrane surface, and promote the plugging and embedding of pollutants into the membrane hole, which is easy to cause deep pollution of the membrane. The CMF equipment used in this experiment can adjust the working pressure indirectly through the flow rate. The experimental results show that, when the flow is not controlled at the initial stage of filtration, the flow attenuation is fast, and the time remaining above 33.3L/(h·m2) is only 4h. After 8h, it is reduced to the low limit flow of 15.0L/h. After the implementation of flow control, the time remaining above 33.3L/(h·m2) can reach 6h. The flow rate remained at 28.3L/(h·m2) after 9h.

Effects of CMF filtration on main physicochemical indices of red wine

The main physicochemical indexes of wine were tested in the experiment. After CMF filtration, the stability and bacterial indexes of wine reached the standard, and the main physicochemical indexes such as alcohol intensity, total acid, volatile acid, pH value, chroma and tannin had little change, while the indexes of reducing sugar, total SO2 and free SO2 were slightly reduced. Figure 1 shows the changes of pentosan in liquor before and after ultrafiltration.

There are differences in physical and chemical index detection and sensory evaluation between membrane separation and dead-end filtration.

In the early stage of red wine filtration, some large particles, such as residual pulp fibers and proteins, are mainly able to affect the membrane flow. They are adsorbed on the membrane surface through various mechanisms (electrostatic action, hydrophobic effect, charge transfer, etc.), but these large particles will not completely block the membrane pore, and the amount is small, which has little influence on the membrane permeability. However, when the adsorption of these large particulate matter reaches a certain degree (in the middle stage of filtration), the material flow velocity in some areas of the membrane surface will be significantly reduced, resulting in the precipitation and accumulation of fine impurities in this area, forming concentration polarization, and the flow attenuation amplitude will increase. Due to the existence of tangential velocity, the flow attenuation trend can be suppressed to achieve equilibrium (in the later stage of filtration), and the “bridging effect” of large particulate matter in the early stage prevents small pollutants from embedding into the membrane hole and causing deep pollution, thus forming a relatively stable flow rate in the later stage of filtration. This analysis can also be verified in the efficient regeneration of CMF filter membranes.

To sum up, due to the termination of fermentation in the middle, the sugar fermentation in the wine is not complete, so the sugar content of low-alcohol wine is slightly higher. Due to low alcohol, easy to be infected with miscellaneous bacteria, so, for the late sterilization requirements are very high. Hollow fiber membrane can be used for ultrafiltration of low alcohol wine to remove bacteria in wine, reduce the loss of wine and the formation of wine feet, and increase the production of finished wine. Reduce the effect of oxidative Browning substances and bitter astringent ingredients.

Post time: Jan-06-2023