Concentrated juice refers to fruit juice that has been extracted and then partially evaporated to remove water, resulting in a higher concentration. Some concentrated juices may have a sugar content exceeding 65°Brix. When making juice, an equal amount of water (equivalent to what was evaporated during concentration) is added back to the concentrate to dilute it, producing reconstituted juice. Compared to fresh juice, concentrated juice has a higher concentration, offering advantages such as higher density, lower cost, easier transportation, convenient storage, and stable quality. It is widely used in tea and beverage shops for making various mixed drinks. However, compared to freshly squeezed juice, some active components are degraded, nutrients are lost, and the flavor may change.

Currently, thermal concentration is the primary method for producing concentrated juice. The physical and chemical reactions induced by heat treatment directly affect the color, aroma, and taste of the juice, as well as degrade its bioactive compounds. Common thermal concentration methods include atmospheric heating and vacuum heating.

Atmospheric Heating Concentration:​ During heating, boiling water generates a large amount of steam, which drives the evaporation of moisture from the juice. The non-volatile components remain, increasing the concentration of soluble solids.

Vacuum Heating Concentration:​ This method preserves more beneficial components than atmospheric heating. By reducing the boiling point of the juice under negative pressure, water evaporates quickly at lower temperatures, improving efficiency, minimizing the loss of heat-sensitive compounds, and enhancing product quality.

Non-thermal concentration techniques include freeze concentration and ice-temperature concentration, both conducted below freezing. Compared to thermal methods, these techniques better preserve the original flavor and color of the juice.

Freeze Concentration:​ Part of the water in the solution is frozen into fine ice crystals and removed from the liquid phase to achieve concentration. While this method retains flavors, aromatic compounds, and vitamin C effectively, its efficiency is low—it cannot concentrate juice beyond 55%. Additionally, removing ice crystals may carry away some juice, causing losses. Freeze concentration also fails to deactivate microorganisms or enzymes, requiring further sterilization or frozen storage.

Ice-Temperature Vacuum Concentration:​ Conducted under negative pressure, this method dehydrates juice at temperatures below freezing but above the ice point. It slows physicochemical changes, reduces polyphenol degradation, and clarifies the juice. Compared to freeze concentration, it requires slightly higher temperatures, preserving the juice’s original color without extreme cold. Ice-temperature concentration retains nutrients well and is cost-effective in terms of equipment.

Reverse Osmosis (RO) Concentration:​ A membrane separation technology that uses pressure and concentration gradients to purify and concentrate solutions. RO does not require heating, operates at room temperature without phase change, and minimizes volatile aroma loss, reducing solid loss to as low as 1%. It preserves the juice’s natural flavor, clarifies it effectively, and consumes less energy than thermal or freeze methods. Since RO is performed in sealed pipelines, oxidation is avoided. However, standalone RO has limited functionality and must be combined with ultrafiltration and vacuum concentration for optimal results. This technology is still developing and is mainly used for pre-concentrating juice.

From Freshco Industry ltd