Vacuum degassing to remove unwanted components from the liquid
Gas dissolved in a liquid can be annoying. Oxygen can degrade the beverage, and carbon dioxide changes the pH, making bottling more complicated. At this point, these gases can be removed using a vacuum.
Anyone who leaves a cup of fresh tap water at room temperature or heats a pot of water knows a phenomenon: as the water temperature rises, bubbles form on the wall or bottom of the glass. They mainly contain carbon dioxide and oxygen. These gases enter the water from the air, most of which are already in the water at the waterworks. In the waterworks, the water is repeatedly aerated during the treatment. In particular, these two gases will dissolve in the liquid.
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At the beginning of the 19th century, British chemist William Henry found that the solubility depends on the partial pressure of the gas and the temperature of the liquid. It rises with increasing temperature and decreases with decreasing pressure.
Gas will affect shelf life and taste
In the production of juices, wines, beer and soft drinks, even small amounts of gas can quickly develop into undesirable factors. For example, dissolved oxygen promotes bacterial growth and destroys vitamin C and other antioxidants. This can affect the odor, taste and shelf life of the beverage, as well as discoloration and loss of appetite. The dissolved carbon dioxide floats the fiber portion and the fruit pieces and then deposits on the surface. Free bubbles also promote the formation of foam, especially in previously heated beverages. In this case, it is often necessary to drastically reduce the pouring speed.
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The vacuum can subtly remove unwanted gases from the processed liquid. For example, in a spray degassing process, water is sprayed through a nozzle into a vacuum vessel having a pressure of less than 300 mbar.Under the negative pressure of the degasser, the bubble expands and ruptures.
With/without stripping gas
Film degassing is mainly used to produce juice, wine and beer. In the cylindrical container, the beverage liquid flows around the hollow fiber membrane, and the hollow fiber membrane allows only gas to pass. The dissolved gas penetrates the membrane and the vacuum pump draws it out by suction. In order to keep the residual gas content as low as possible, it is also possible to use a stripping gas on the gas side. Nitrogen is usually used for this purpose. In any case, a vacuum is applied to the gas side. The pressure drop "sucks" out the dissolved gas from the liquid.
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For the production of gas-free mineral water requiring a particularly low residual oxygen and carbon dioxide, degassing is accomplished by several columnar vessels in series. A similar process exists in the chemical industry where it is desirable to avoid adverse reactions of liquid components.