Figure 1 below shows a fruit juice process with multiple potential sources of particles and organisms and possible locations for filters to help control or remove them.
Filtration in Juice Production
Raw juice has a very high load of particles and organisms, even after bulk filtration. The cartridge filters shown in the figure are used to remove the particles and organisms that may adversely affect product quality and safety.
Of particular concern are organisms that are known to survive heat treatment and are common in some juice processes. Organisms such as “thermo-acidophilic bacteria”, or TAB, especially Alicyclobacillus species, occur naturally in fruits and are resistant to pasteurization. Other heat-resistant, "flat sour" organisms can enter the process with outside ingredients. Sugar, for example, can be a carrier of the spores of Bacillus and other bacteria and mold species.
Visit our application pages to learn more about how filters are used to protect your product quality.
As ingredients are brought into the process, removal of sediment and other suspended particles helps control product quality. Unwanted particles are removed to begin clarifying the product and reduce the amount of material that could create off flavors. Housings marked “1” in the figure are chosen depending on the level of particle content in each ingredient. Performed using depth filtration media, the filters can remove only visible particles (> 20µm) or smaller particles (>5µm) according to process requirements.
While sediment removal is an important first step in creating clear juice products, the further removal of particles and organisms is another critical filtration process for clear juices. The choice of pore size and media for the final clarifying filter (housings marked "3") depends on the level of particulate in the juice. Depth media with pore sizes of 1 or 3 microns may be appropriate. Some producers may choose sub-micron rated depth media. Membrane filters are not usually used at this stage.
There are many possible bacteria and molds that could enter the process, but all can be removed just before packaging using membrane filters. Organisms can enter the bottle from two directions. The water itself can carry organisms. Even spring water from an underground source has some bacteria. The bottles can also bring organisms from the environment or from the water used to wash and rinse them.
Housings marked "6" in the figure are in place to capture most, though not all, of the fine particles and organisms that are in the product water or package wash/rinse water just before packaging. The filter is usually a membrane filter with pore sizes of 0.45µm to 0.65µm. This filter captures the bulk of the organisms and protects the critical final filter from being overloaded and fouling prematurely.
Immediately before the juice is packaged, the final filter removes the last of the spoilage organisms from both the final product and water used to rinse containers. The result, if the correct filter is chosen, is a clear juice with the flavor and color desired by consumers. The key is choosing a filter designed to allow flavor elements and color to pass while capturing the bacteria that could cause spoilage.
Filters used for this final step are membrane filters with 0.45µm or 0.65µm pore sizes, though the filters for water filtration may have 0.22µm pore sizes. The filters for product are designed with membrane structures that will capture the bacteria, but allow color bodies and the flavor elements to pass. Each producer chooses the appropriate filter based on testing and the nature of the organisms that must be removed. Critical Process Filtration partners with juice producers to test and validate the performance of filter designs and to create filtration systems that produce the best and safest product in the most cost-effective way.
Ingredients may be stored in tanks before mixing and the final product is usually stored for staging before packaging. Filtration acts as a critical contamination control step protecting ingredients and final product from particles to environmental organisms. For juice operations, the vent filters act as a barrier to prevent airborne contaminants such as dust, bacteria and mold from entering the tank and potentially spoiling the product.
Hydrophobic membrane filters are used for this filtration application. The hydrophobic nature of the membrane prevents water droplets from collecting on and wetting the membrane, which would block the flow of air and lead to tank failure. Tank vent filters with 0.22μm pore sizes are usually used because of their ability to block bacteria from entering the tanks.
Normal atmosphere is sometimes not allowed to contact the final product in the final package. This is done if oxygen might promote the growth of undesired organisms or cause oxidation of the product that affects flavor quality. Normal air may be replaced in containers with process gases – usually nitrogen, carbon dioxide or a combination. As the containers are filled, a process gas "blanket" is injected into the container to displace air before container closure.
The process gas filter (housing 6) assures that no particulates or bacteria are carried by the gas to the container. In most facilities, hydrophobic 0.22µm membrane filters are used to make sure all bacteria are removed.
The figure above shows the filter locations for the juice process as the ingredients are brought to the final mix and packaging facility. Ingredients could also be produced inside the facility and filters may be used in those processes. Critical Process Filtration can help with system design for filters used in ingredient production, as well.