Cross-flow filtration of fruit juice

3. Juice Production

The steps and the process parameters followed during the production of cherry and black currant juice at Vallų Saft are shown in appendix 1 and 2. The production process of these two types of juices is quite similar, and it is done according to the following procedure:

The cherries or berries are deposited in the buffer tank. During summer, the fresh fruits are transported to the crusher with the help of a conveyer belt (capacity: 20 tons/h), and the rest of the year, frozen berries or cherries (approx. 0° C) are transported with the help of a defrosting conveyer belt (capacity: 10 tons/h)

Crushing

The berries or the cherries are crushed differently depending on the type, and approximately 25% of the stones are crushed when producing cherry juice. In this way, chemical compounds, i.e. benzaldehyde and hydrogencyanide, are released

Spiraflow

	The crushed fruits are pumped to the spiraflow (capacity: 20 tons/h) with a max. pressure of 40 bar
	The fruit mass is heated to approximately 75oC in the spiraflow. The running time is 8 min and the holding time 2 min. The fruit mass is heated in order to denature the undesired enzymes found in the berries or cherries, i.e. perioxidase and polyfenoloxidase. These enzymes oxidate the phenols
	The fruit mass is cooled down to 45–55oC before enzyme treatment

Enzyme treatment

Enzyme treatment is different for cherries and black currant. Black currant contains a larger amount of pectin. Pectin polymers have the capability of developing stabilising gels in contact with water. These polymers should be destroyed in order to achieve an acceptable yield. 8–10 l of pectinase are used per 20 tons of berries. The enzyme treatment takes place for 2-6 hours (depending on the amount of pectin) at 50oC. Occasionally, ½ - 1 l of pectinase per 20 tons of cherries are added when producing cherry juice. In this case, the enzyme treatment takes place for ½-1½ h at 50oC

Pressing

The fruit mass is then pressed in batch of 500-1500 kg. At Vallų Saft, there are 3 bucher pressers with a pore size of 5 mm2, and between 4 and 7 tons of fruit mass are pressed per hour

Pasteurisation

	The juice coming from the presser is pasteurised for 60 seconds at 98oC with a flow of 18 tons per hour
	After pasteurisation, the fruit mass is cooled down to 45-50oC

Clarification

During clarification, 0.6 kg of gelatine dissolved in 40 l of water are added to 20 tons of juice. All this is stirred for 5 min both before and after adding 5 kg of kieselsol. This step takes place for 2-6 hours, depending on the sedimentation. Gelatine is a collagen protein, which attaches to polyphenols and pectines. These floculant formations get attached to some other components, i.e. kieselsol, and finally they sediment. During clarification some enzymes can be added in order to help the sedimentation: pectinase (½-2 l pr. 20 tons) when producing black currant juice and amylase (2 l pr. 20 tons) when producing cherry juice. Amylase breaks down starch, resulting in an increase on the efficiency and rate of the sedimentation process

Filtration of sludge

After clarification, the juice is separated in two: the supernatant or top juice and the sediment. The top juice is centrifuged at 45° C in order to remove the flocculant agents. The sludge obtained after centrifugation follows the same procedure as the sludge obtained during sedimentation. Both are pre-filtered at 45° C through a vacuum filter. 440 kg of perlite (filter aid) are added to 60-100 tons of juice. The transmembrane pressure (TMP) should be 0.4-0.5 bar and the vacuum filter has a capacity of 5-8 tons per hour. This step takes place for 10 hours. After that the filter is rinsed and more perlite is added

Pressure filter and ultrafiltration

The centrifuged and vaccum filtered juice is thereafter filtered through a pressure filter or an ultrafiltration system. The pressure filter has a pore size of 50 mm and 80 kg of kieselguhr are added per 80-100 tons juice. The temperature should be approximately 8oC, and the TMP 2 bar. The capacity of the filter is between 5 and 12 tons per hour, and this step takes place for 10 hours. After that the filter is rinsed. Ultrafiltration is carried out at 45-50oC, the cut off value is 200,000 Dalton (approximately 0.2 mm), the TMP is 4.5 bars, and the capacity of the system is approximately 4-14 tons per hour for 10 hours. The retentate obtained after ultrafiltration is centrifuged. It might be necessary to filter the juice again through the pressure filter after ultrafiltration when producing cherry juice due to the precipitation of some compounds during cooling

Pasteurisation

The filtered juice should be pasteurised at 98° C for 30 seconds when producing aseptic juice. The aseptic juice is stored in a sterile tank at 10oC. The yields for black currant and cherry juice are approximately 90% and 83%, respectively.

Evaporation

The filtered juice should be cooled down to 5oC when producing concentrated juice, if this is not evaporated on the same day. Evaporation can take place in two different ways: the filtered juice is either evaporated at 95oC from 12 to 23-25oBrix or processed through a 2-steps system (also called turbo). The final evaporation from 23-25 to 68oBrix takes place on a 4-steps system at 90-98oC with a flow between 8 and 14 m3/t. The concentrate is stored in a sterile tank at 10oC

In order to control the process, different analyses and measurements should be performed during production (appendix 3). A batch should meet all the quality requirements after each step.