The process of clear concentrate production

• 1.Raw material

Sour cherry, apple, grape, and pomegranate are the main raw material to produce clear concentrate. Pear and quince also are used for both clear and cloudy concentrate production.

• 2.Washing

To separate external components such as soil, sand, dust, leaves, etc., and eliminate possible insecticides on the fruits, they should be washed. In addition, this step reduces the microbial load of fruits to a certain amount.

• 3.Separation

The juice should be made of healthy, fresh, and edible fruits. Furthermore, the material composition of the fruits may differ based on the degree of ripeness and can affect some properties of the fruit like color and taste. Therefore, separating rotten, crushed, etc. fruits must be done before other processes.

• 4.Destalking

This step runs on sour cherry and grape. The sour cherry deerstalking machine has numerous rubber rollers with adjustable distances, which move in opposite directions. Sour cherry tails are stuck between the slope rollers and are separated from fruits.

• 5.Crushing

For efficient pressing, fruits should be crushed and cell walls break first. Therefore, sour cherries and grapes pass through two rollers with an adjustable distance that rolls in opposite directions. It should be noticed that excessive breaking of the sour cherry cores leads to dissolving the core amygdalin in the juice. The produced hydrocyanic acid resulting from amygdalin and benzaldehyde decomposition (almond aroma) influences the juice quality which should be avoided. Apple, pear, and quince are chopped in a fruit mill. Chopped fruit is called “mesh”.

• 6.Mesh heating

The activity of two enzymes ortho-diphenyl oxidase and par-diphenyl oxidase (naturally found in fruits) causes fruit browning (enzymatic browning) as soon as the tissue disintegrates. Substrates of this reaction are often from the ortho-dihydroxy phenol group of the compounds.

To avoid the negative effects of this process, thermal enzyme deactivation is one of the essential methods. Sour cherry and grape mesh is heated at 85-90˚C for 2-4 minutes. Double-walled tubular heat exchangers are commonly used for this purpose. In this system, water steam is used to heat the juice. For cooling it by 50˚C (for fermentation), cold water is used.

Mesh heating is generally eliminated in the case of fruits like apples, pears, etc.

• 7.Mesh fermentation

Fermentation is a series of biological actions performed by enzymes. In addition to pectolytic activity, the applied enzymes have cellulosic, hemicellulosic, and proteolytic activity too. The added enzymes make cell rupture easier during the pressing step and increase pressing efficiency. Based on the enzyme’s activity, 10-20 g solid enzyme and 100-200 ml liquid enzyme per 1000 kg mesh enzyme is needed. The optimum temperature for maximum enzyme activity is 45-50˚C and the active period of the enzyme is 1-2 hr., depending on the type of enzyme. The optimum amount of enzyme is specified by the “drop test”.

• 8.Pressing

Among different methods of extracting fruit juice from mesh (diffusion, liquefaction, etc.) pressing is the most common method. Based on the working method of the press, there are two types of it: continuous and non-continuous. In addition, the press efficiency may be different depending on the press type, the juice composition, and the juice yield of the fruit. For example, depending on the press type, the juice yield in apple, grape, and sour cherry is 65-83%, 70-85%, and 65-75% respectively.

• 9.Dearomatisation

Dearomatisation is a step before concentration or clarification. To achieve a better and more natural aroma, dearomatization is better be done before clarification. The dearomatization system consists of different sections including evaporator, fractional decomposition, and cooler. To get 1-liter aroma concentrate, 150-250 liter juice should be concentrated (0.4-0.6%). The obtained aroma concentrate will be added to the concentrate again in the dilution stage to make the juice.

• 10.Clarification

The temperature of outflow juice from the de-aromatization system is 90-92˚C. The juice temperature in the clarification tank is 45-47˚C. Destination and starch disintegration is done via an enzymatic method. Then, the fluctuation (clot) is created at the same temperature or at 20-25 ˚C by adding auxiliary materials. The juice stays in the tank until the clot is settled. The clot is separated from the juice afterward or it is done by flotation.

• 11.Filtration

Plate or cover filters are used to filter the juice. Recently, vacuum filtration is in use commonly.

• 12.Concentration

The clear juice is stored after concentration. In addition to volume reduction, the advantage of this method is to preserve the concentrate against microbiological spoilage and chemical changes.

These three methods of concentration:

• A.Thermal concentration
• B.Freezing concentration
• C.Reverse osmosis concentration

Thermal concentration is the most common among other methods that are done in an evaporator. There are different types of evaporators including tube, plate, film cutter, and centrifuge. At the end of this process, the dry matter of the juice is 70-72%.

In the freezing concentration method, the juice freezes and depending on the coldness, some amount of its water turns to ice. A separator separates the frozen portion and the dry matter in it is increased. For example, if the apple juice contains 11% dry matter, 81% of the juice water is separated in form of ice at -5 to -8 ˚C freezing temperature. Then, the dry matter percentage increases by 40%.

The freezing concentration method needs less energy compared with the thermal concentration method (80 kcal is needed for freezing 1 kg water which is 30% of the three-stage evaporator in the thermal method). However, expensive form of energy, which is used in this method and costly installation and machinery, has made this system’s application 2-7 times more expensive compared with a thermal method. Therefore, freezing concentration method is only used limitedly in case of the orange juice, which is sensitive to the heat. The final dry matter depends on the juice viscosity, which is about 40-50% for fruit juices.

The mechanism of the reverse osmosis method is as follows:

The juice passes through a selective membrane under higher pressure than the osmotic pressure of the system. In this situation, water along with some other small molecules of the juice selectively passes through the membrane, and depending on the membrane permeability and pressure, the juice dry matter can increase by a maximum of 25% economically.

• 13.Storing

The temperature of the outflow concentrate (40-60˚C when leaves the evaporator) must be reduced for storage. The storage condition depends on the percentage of the concentrate dry matter (Brix). If the dry matter percentage is 68-72%, it can be stored in stainless steel tanks or suitable barrels at 4˚C but if it is less than that, other methods like freezing, hot filling, or sterile filling should be used.