Reprocessing of NFC

In the USA, some NFC is moved in bulk by road and rail tankers to juice packers across the coun- try, but most NFC is fi lled into retail packages in Florida and dis trib ut ed from there. Shipping from Florida to Europe in bulk is done in fro zen drums and aseptic bag-in-box con tain ers. For Brazilian NFC, overseas shipping also occurs by bulk sea tanker. Overseas shipping of pack aged prod uct is at a cost disadvantage compared with ship- ping bulk juice. Moreover, the additional delay in transport time adds to dif fi cul ties with logistics and fore cast ing for the packaged product.

Traditionally, NFC taken from storage at the fruit processor’s site for reprocessing is blended with juice from a different part of the season and/ or with pulp. The juice blend is then repasteurised prior to fi lling into consumer pack ag es.

Alternatively, specially designed equipment can be used to transfer juice from aseptic bulk bags to consumer packages, via an aseptic tank, without the need for repasteurisation.

When NFC is shipped overseas, blending with other orange juice varieties and pulp may take place at the juice facilities at the reception

5.6 NFC production

Frozen concentrate storage Evaporator

Concentrate blend tanks

Plate cooler Essence recovery Condensate to fruit washing Juice from clarification

5.7 Concentrate production

Globally, most orange juice is produced as con cen trate. Juice from the clarifi cation step is evap o rat ed to remove most of the water (see Fig ure 5.15). Currently, the most widely used cit- rus evaporators are of tubular design, although plate and cassette evaporators are also installed in citrus plants.

The evaporators are designed for the enormous juice volumes commonly processed in large citrus plants, where evaporator capacities can exceed 100,000 kg/h (about 220,000 lbs/h) of water evapo- rated. Versions with as many as seven effects are installed (seven effects means basically that the steam is reused to evaporate water in seven steps). Such systems have a very low specifi c steam con- sumption; only 1 kg (2.2 lbs) of steam is used to evaporate 6 kg (13.2 lbs) of water. However, ad- ditional effects increase the residence time for the product in the evaporator accordingly.

During the 1970´s and 1980´s, there was a large expansion in concentrate capacity in the ma jor citrus markets of Brazil and Florida. To day, lit tle increase in evaporator capacity is need ed in these regions, but new evaporators are being in stalled to satisfy the requirements of oth er expanding orange-producing regions.

5.7.1 TUBULAR EVAPORATOR SYSTEMS The most common type of tubular evaporator

system used for orange juice is the TASTE evap o ra tor. It is generally described as a con- tin u ous, high-temperature short-time evap o ra tor of the long, vertical tube falling-fi lm type. The name is an acronym for Thermally Ac cel er at ed Short-Time Evaporator. It was designed and de vel oped in Florida, and today this type of evap o ra tor is manufactured in many dif fer ent coun tries. These evap o ra tor sys tems are ded i - cat ed to citrus fruit.

Fig. 5.15 Flow chart of concentrate production. 5.7 Concentrate production

1 Preheated juice Steam Steam Condensate Concentrate

65 °Brix _{Juice 12 °Brix} = Product stage 1 2 7 6 5 3 4

A fl ow diagram of an evaporator with seven product stages is pre sent ed in Figure 5.16. The juice is fi rst preheated to 95–98 °C. Holding at pas teur i sa tion temperature stabilises the juice by means of mi- crobial and enzyme inactivation. The prod uct then passes through a number of stag es un der vacuum until a concentration of up to 66 °Brix is achieved. By this time the product tem per a ture has fallen to about 40 °C. The res i dence time in the evaporator is typically 5–7 min utes or longer.

Good distribution is of primary importance in the design of an evaporator. It ensures that all the product is uniformly treated and that the heat ex- change surface is used to its maximum potential. A special feature of the TASTE evap o ra tor is the way in which the product is distributed across the tube bundle. The juice is fed into the distribution section at a temperature and pres sure greater than in the entry zone of the tube bundle. The liquid is fed through a diverging ex pan sion

nozzle which converts all the product into a liquid/vapour mixture. The expanding va pour accelerates the liquid/vapour mixture through a second nozzle and cone assembly. Fur ther fl ash expansion of the vapour causes at om i sa tion of the liquid phase into a turbulent mist. The accel- eration effect can cause mist ve loc i ties to exceed

50 metres/second on leaving the tube bundle! The high degree of turbulence increases heat-transfer rates and reduces burn-on, which helps to achieve long operating runs.

Other tubular evaporation systems

There are also other tubular evaporator sys- tems of similar design for citrus plants, which in clude a conventional mechanical method of dis trib ut ing product across the tube bundles. They in cor po rate thermal recompression to in crease steam economy without increasing res i dence time. Rel a tive ly few of these evap- o ra tor sys tems have been in stalled for high prod uct ca pac i ties.

5.7.2 PLATE AND CASSETTE EVAPORATOR SYSTEMS

In addition to tubular systems, plate and cassette evaporators are also used for concentrating or- ange juice. As the name implies, plate evapora- tors consist of plates clamped together in a frame with gas kets between them. It is more common to use cassettes (welded double plates) instead of single plates because they further simplify main- tenance. The heating medium (steam or vapour) fl ows through the space between the welded plates that make up the cassette.

Fig. 5.16 A simplifi ed fl ow diagram of a tubular evaporator. 5.7 Concentrate production

Product channels are formed between individual cassettes separated by gaskets. This confi guration allows ready inspection of product.

Some advantages of plate/cassette evaporators when compared with other types of evaporator are that capacity increases are easily achieved by add ing more cassettes, and that maintenance and inspection are easily carried out by opening the frame. Furthermore, as cassette evaporators are more compact, they eliminate the need for several walkways at different levels used to access the equipment as found with tubular systems. The one- level confi guration offers easy operator control and ready access for maintenance activities.

A small tem per a ture difference between the product and heating medium is suffi cient in this type of evap o ra tor. This al lows lower operating temperatures to be used than with traditional tubular evap o ra tors. The main type of cassette evaporator is the rising fi lm unit.

Rising fi lm cassette evap o ra tor

In the rising fi lm cassette evaporator the prod uct enters the bottom of the cassette and rises up over the heating sur face as it boils (Figure 5.17). No mechanical feed distribution device is need ed and even dis tri bu tion is achieved through gravity.

The fi lm fl ows upwards in a homogenous fl ow thus giving a very short retention time over the heating surface. The liquid/vapour velocity at the outlet of the very short heating channel is very high. It is pos si ble to evaporate prod ucts of higher vis cos i ty and higher pulp content than in a falling fi lm evap o ra tor.

As plate systems can be designed for fl exibility, some installations installed in citrus plants are used to process other types of juice outside the orange juice season.

5.7.3 HOMOGENISATION

Sometimes, homogenisation of concentrate is car- ried out within the evaporator system. Product then normally passes through a homogeniser be- fore the last effect. At this stage the concentration is approximately 40–42 °Brix. Homogenisation breaks down the pectin, thereby lowering the viscosity of the concentrate. This increases the effi ciency of the fi nal stage of the evaporator. It is also claimed that homogenisation reduces the sinking pulp level in the product. This could permit juice with higher pulp levels to be fed to the evaporator.

In the case of special requirements of concen- trate with very low pulp content (<1 %), specially designed hermetic clarifying centrifuges may be

Fig. 5.17 A rising fi lm cassette evaporator.

In document The Orange Book (Page 86-89)