1. Field of the Invention
The present invention relates to freeze-concentrating techniques for liquids, such as brines, fruit juices, coffee extracts or enzyme extracts. More particularly, it relates to techniques for separating target components from water (ice) in frozen substances and slurries and recovering concentrates of the target components.
2. Description of the Related Art
Freeze-concentrating methods are known for preparing concentrated liquid substances from liquids, such as brines, fruit juices, coffee extracts or enzyme extracts. In known freeze-concentrating methods, a crude liquid is frozen under low-temperature conditions in order to generate a slurry containing ice and a portion containing concentrated target components. Then, the ice and the concentrate are separated. According to this method, the amount of energy required to concentrate the target components can be reduced to approximately {fraction (1/7)}th of the amount of energy that is required for evaporation methods. Moreover, because the concentration steps are performed at low temperatures, denaturation of concentrates owing to heat or desorption of aromatic components can be reduced. Accordingly, known freeze-concentrating methods can be used to prepare high quality concentrated components (concentrated fruit juices, etc.) from diluted liquids, such as fruit juices or coffee extracts, while minimizing the amount of energy necessary to perform the concentration method.
Typical steps for concentrating fruit juice using known freeze-concentrating methods will now be summarized with reference to FIG. 5. First, a dilute liquid 1, such as fruit juice, is cooled to an appropriate low-temperature range, i.e., a temperature that is below the freezing point of water, to form a slurry 2. Target components that were contained in the dilute liquid 1 can be fractionated in a substantially uniform manner from the slurry 2, thereby generating a liquid concentrate. That is, by freezing the dilute liquid 1, a slurry 2 is prepared that contains a solid matter portion (hereinafter referred to as an xe2x80x9cice portionxe2x80x9d) and a concentrated liquid portion. Thereafter, the slurry 2 including the concentrated portion and the ice portion is transferred to a centrifuge 3 and centrifuged to separate the liquid contents from the ice portion. In this manner, the slurry 2 is separated into the ice portion and a liquid concentrated portion 4.
When separating a concentrated portion from a slurry, such as fruit juice, it is important to minimize the loss of the target components. For instance, when a liquid such as fruit juice is frozen, the target components usually adhere to the ice portion or the target components remain occluded within the interior of the ice portion. Therefore, it is necessary to attempt to efficiently recover the target components that remain adhered to the ice portion or that are occluded within the ice portion.
Known methods for recovering such concentrated portions are, for instance, (1) melting the ice portion that remains after centrifugation and repeating the freezing process and the centrifugation process (that is, repeating the freeze-concentrating process) and (2) washing the surface of the ice portion with a dilute liquid or water, whereupon the target components are recovered within the washing liquid.
However, repeatedly performing freezing-centrifugation processes results in troublesome and time-consuming freeze-concentrating processes as a whole and is thus economically disadvantageous. Further, washing the surface of the ice portion of the slurry with a dilute liquid or water and recovering the washing liquid presents a drawback in that, while a portion of the target components that were adhering to the ice portion can be recovered, the addition of the washing liquid results in an increased volume of the concentrated components or in decreased concentrating efficiencies. Therefore, a long-felt need exists for a new means that is capable of minimizing the loss of concentrated components in freeze-concentrating techniques (i.e., improved target component recovery rates), while maintaining high concentrating efficiencies.
It is, therefore, one object of the present teachings to provide improved freeze-concentrating techniques. In one aspect, known problems relating to the recovery of concentrated components are overcome by providing new methods for performing freeze-concentrating processes. In another aspect, new devices are taught that are capable of rapidly recovering concentrated target components that are adhering to an ice portion or that are occluded within the ice portion, while maintaining high concentrating efficiencies.
In a representative embodiment, a rotor unit is taught that comprises a rotating vessel having an outer wall surface through which liquids can be transmitted and a heater unit. The heater unit may be disposed within the rotor, such that the portion of the slurry/ice portion that exists within the rotating vessel closest to the central rotational axis of the rotating vessel is heated by the heater unit. In this manner, the liquid generated from the ice portion that is melted by the heater unit will be transmitted through the ice portion within the rotating vessel to wash out concentrated components adhering to the ice portion before being exhausted from the rotating vessel.
Thus, the portion of the slurry that is closest to the central axis of rotation may be partially melted by means of heat supplied from the heater unit while centrifuging the slurry that remains in the rotating vessel. That is, the ice portion in the slurry can be washed by the melted liquid generated by melting of some of the ice portion of the slurry. Consequently, separation and recovery of the concentrated components that have adhered to the ice portion of the slurry can be efficiently performed.
By using such a rotor unit, it is no longer necessary subject the slurry to a washing liquid (i.e., water or a dilute liquid, such as fruit juice), as is the case for known freeze-concentrating techniques.
In another aspect of the present teachings, the rotor unit is designed, such that liquids discharged through the outer wall surface of the rotating vessel are maintained within the rotor unit during the centrifugation step. According to this design, liquids that have been discharged through the outer wall surface of the rotating vessel can be simply stored in the rotor unit and thus, it is possible to reduce the amount of loss of volatile components as a result of desorption of the volatile components in the concentrated liquid recovered from the slurry (for instance, concentrated fruit juice). Optionally, a liquid transmitting tube can be disposed within the rotor unit to transfer liquid that has been stored in the reservoir unit to the exterior.
In another aspect of the present teachings, a solid-liquid separating device is described that has a supply tube disposed within the rotor unit and that permits the slurry to be introduced into the rotating vessel. In the alternative or in addition to, a discharge tube also may be provided to discharge the remaining ice portion after centrifugation. If both of these features are included, the slurry/ice portion can be easily and smoothly supplied to and recovered from the recovery vessel.
Methods for preparing concentrated components from a dilute liquid are also taught. In a representative method, a slurry that contains an ice portion and a concentrated liquid portion may be centrifuged while heating the slurry. The concentrated components are then recovered. Thus, a concentrated portion is separated from the ice portion. By partially melting the ice portion through heating, concentrated components adhering to the surface of the ice portion can be separated from the ice portion by centrifugal force.
In the alternative, the slurry may be subjected to a first centrifugation without heating and the resulting concentrated portion is recovered. The slurry remaining in the centrifuge can then be subjected to a second centrifugation with heating, and the additional resulting concentrated portion is recovered.
Preferably, during the centrifugation step, the concentrated portion that has been separated from the slurry is maintained within the rotor unit. By maintaining the concentrated portion within the rotor unit during the centrifugation process, it is possible to prevent the concentrated portion from being exposed to the atmosphere outside of the rotor unit. Importantly, this design and method prevents the concentrated portion from being exposed to the atmosphere between the rotor unit and inner wall of the centrifuge housing, where the concentrate portion can rapidly evaporate. Therefore, degradation of the quality of the concentrated components can be minimized.