Abstract:
A method of reducing the ethanol content of a beverage which includes ethanol and volatile component is disclosed. The method may include separating the beverage into first and second streams with the first stream including ethanol and the volatile components and the second stream including ethanol but none or little of the volatile components. The method may also include contacting the second stream with a strip solution to produce a treated second stream to reduce the ethanol concentration. The method may also include mixing the treated second stream with the first stream whereby the ethanol content of the beverage is reduced but the volatile components remain substantially unchanged.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a continuation of U.S. patent application Ser. No. 10/563,636 filed on Mar. 14, 2008. This application is a National Stage of International Application No. PCT/AU2005/000814, filed Jun. 7, 2005, which claims the priority of AUSN 2004903139, filed Jun. 9, 2004 and AUSN 2004907247, filed Dec. 21, 2004. The entire disclosure of each of the above applications is incorporated herein by reference. 
     
    
     FIELD 
       [0002]    The present disclosure relates to a method of reducing the ethanol content of a beverage which includes ethanol and a volatile component. 
       BACKGROUND AND SUMMARY 
       [0003]    The level of alcohol in beverages such as wine is an important determinant of its perceived quality. It is, in turn, largely determined by the level of sugar in the grapes from which it is produced. Low levels of alcohol are commonly associated with grapes grown in cooler climates or seasons. Less positively they are also a result of under-ripe or over-irrigated grapes and in these instances are seen as an indicator of low quality wine. High levels of alcohol are, as a result, deemed to be associated with fully ripe fruit and higher quality. This is not a consequence of the higher alcohol per se but rather the more mature fruit flavours, tannins and lower acidity of grapes picked at optimum ripeness. In fact the pursuit of greater ripeness by winemakers in many parts of the world has resulted in wines with excessive alcohol. Besides increasing the intoxicating effect of the wine, this manifests itself in a reduced perception of wine aroma as well as an unpleasant hotness on the palate. 
         [0004]    A measure of the extent of this problem shows it is growing at a worrisome rate. Wine samples analysed by the Australian Wine Research Institute over the past 20 years have shown a steady increase in alcohol level over this period so that the mean for all samples analysed in 2002 was 14.2% compared with 12.4% in 1984. These elevated alcohol levels can have other damaging effects on wine quality such as prolonged or arrested primary and secondary fermentations, leading to higher levels of residual sugar, with consequent microbiological spoilage, loss of SO.sub.2 and oxidation. (AWRI 2003 Annual Report p 44). 
         [0005]    A method for removing some of this alcohol would allow winemakers to pick their grapes at optimum ripeness from the point of view of flavour maturity without suffering the negative effects of excessive alcohol. 
         [0006]    Processes for reducing alcohol have been offered previously but all are deficient in some way. 
         [0007]    The simplest method for reducing alcohol is to add water to the grape must or wine. While this has been practised for centuries, it diminishes wine quality by reducing the overall concentration of the wine. It is also illegal in many jurisdictions. 
         [0008]    A more effective procedure is to remove alcohol using a low temperature distillation technique such as the spinning cone. In this, volatile components of the wine, including alcohol, are removed in the distillate and the volatile flavours are separated from this and returned to the wine being treated. This system is complex, capital intensive and immobile. There is also some possibility of flavour loss, but most importantly, the alcohol is removed at relatively low strength (&lt;50% v/v) so overall volume loss from the wine is significant. 
         [0009]    Another technique is proposed in Patent Specification No. AU B 42319/93. In this proposal wine is processed through a reverse osmosis plant to generate a permeate stream which consists substantially of water, alcohol and low concentrations of some other minor components. The permeate stream is then distilled in a high energy distillation column and the distillate which consists very substantially of high strength alcohol, is removed as a useful by-product. The residual material, being dealcoholised permeate, is returned to the wine, thus reducing its alcohol content. This is effective but costly in energy terms as well as infrastructure costs. 
         [0010]    According to Williams Williams L. Distilled Beverage Technology, course notes, UC Davis 1981, “Because of this non-ideality, the relative volatility of ethanol with respect to water varies greatly. It is very large (10 to 11) in dilute solutions and decreases to 1.0 at the azeotropic concentration . . . . Thus alcohol enrichment is very large at low concentrations and one may say that distillation is “easily achieved” in this region. At high alcohol concentrations, the enrichment is small and thus, distillation to very high concentration is “difficult or costly” (in terms of energy, equipment size or both).” 
         [0011]    As well, in many jurisdictions distillation is strictly regulated because of the inherently hazardous nature of the high strength alcoholic spirit produced as well as its interest to taxation authorities for excise revenue purposes. This means that the distillation process must be conducted in licensed premises which are usually remote from the wine being processed. This necessitates the wine or permeate being shipped from the winery to the distillation premises and the dealcoholised permeate being returned. Besides the freight costs and delays of this, in some jurisdictions it is mandatory for the dealcoholised permeate to be recombined only with the wine from which it was originally removed. This means batches must be handled discretely, reducing the prospects of scale economies and, more importantly, the dealcoholised permeate is microbiologically unstable and will quickly deteriorate unless preserved by refrigeration or chemical stabilisers. 
         [0012]    Another option practised in jurisdictions where this is allowed, is to remove a certain amount of permeate by reverse osmosis and to replace it with the same amount of water. This water could be from grape or non-grape sources according to the local regulations but in most wine producing countries the practice is illegal or of dubious status. Another deficiency of this approach is that the permeate which is discarded does contain some other, minor components that would be lost and so the quality of the wine may be slightly diminished. 
         [0013]    An approach described by Hogan et al: Osmotic Distillation Chemical Engineering Progress 1997 and A New Option: Osmotic Distillation, Chemical Engineer Progress July 1998 uses the process of evaporative perstraction to remove alcohol from wine. This technique is also disclosed in Patent Specification No. AU 199717793 B2 and involves passing a stream of wine through a membrane contactor such as a Liqui-Cel™ Extra-Flow produced by Membrana. Separated from the wine stream by an hydrophobic membrane, a counterflow of water is passed through the same contactor and alcohol passes through the membrane from the wine to the water. This process is based on the principle that ethanol, as a volatile wine component, has a significant vapour pressure. This leads to its movement into the porous matrix of the hydrophobic membrane and by virtue of the concentration difference across the membrane, its subsequent dissolution into the water on the other side. 
         [0014]    In practice this results in high levels of extraction of other desirable volatile components from the wine, such as flavours, esters and sulphur dioxide. One approach suggested by the developers of this technique was to “spike” the strip solution with these compounds so that no concentration gradient for the compound exists. This is complex and expensive and renders the by-product less useful. Other efforts to limit the extraction of desirable volatiles by recycling some of the strip stream reduce the efficiency of the process. Efficiency is also compromised by the presence of relatively large concentrations of CO.sub.2 and other gases in wine. These cannot easily be removed without also removing desirable volatiles. 
         [0015]    The object of the present invention is to provide an improved technique of dealcoholisation of beverages which minimises extraction of desirable volatile components from the beverage. 
         [0016]    According to one aspect of the invention there is provided a method of reducing the alcohol content of an alcohol containing beverage including the steps of: (i) processing the beverage by reverse osmosis or nanofiltration for producing a retentate and a raw permeate which includes alcohol; (ii) contacting a first side of an hydrophobic microporous membrane with said raw permeate; (iii) contacting a second side of the membrane with a strip solution to extract alcohol therefrom to form a dealcoholised permeate; and (iv) combining the retentate with the dealcoholised permeate to form a dealcoholised beverage which has an alcohol content lower than that of the beverage. 
         [0017]    Preferably, the strip solution and/or the raw permeate are heated prior to contacting the microporous membrane. It is further preferred that the strip solution and raw permeate are both heated prior to contacting the porous membrane. It will be appreciated that there will be heat conduction between the permeate and strip solution if they are not at the same temperature and therefore it would be possible, although less desirable, to heat one or other of these solutions. 
         [0018]    Normally volatile components in wine are destroyed if the wine is heated. In the process of this aspect of the invention, however, the wine itself is not subjected to elevated temperatures but rather the permeate only is subjected to elevated temperatures. Accordingly, superior alcohol strip can be achieved without degradation of the components in the wine which give it taste and aroma. Stripping at elevated temperatures is much more efficient than stripping at lower temperatures. In the aforementioned article by Hogan et al., the stripping is necessarily carried out at low temperature otherwise the properties of the wine would be seriously downgraded. Accordingly, the process of this aspect of the invention is more efficient than that described in the aforementioned article. 
         [0019]    Preferably, the strip solution and/or the raw permeate has a temperature in the range from about 45° C. to 50° C. when in contact with said microporous membrane. 
         [0020]    Normally the dealcoholised permeate will be at approximately the same temperature as the strip solution and preferably the method includes the step of cooling the dealcoholised permeate prior to recombining it with the retentate. 
         [0021]    In the process of the invention, the beverage itself is not subjected to evaporative perstraction but rather the alcohol rich permeate is subjected to the evaporative perstraction. The beverage is also not subjected to elevated temperatures. 
         [0022]    Preferably the step of processing the beverage by reverse osmosis or nanofiltration is maintained at a temperature in the range from 13° C. to 25° C. 
         [0023]    Where the beverage is wine, the extraction of volatiles is reduced because of their limited passage from the wine into the permeate stream. This is controlled by the selection of appropriate membranes and operating parameters such as temperature, pressure and flow rate to maximise the passage of ethanol while limiting the passage of other compounds. 
         [0024]    Further, the efficiency of the evaporative perstraction process is improved by reducing the concentration of non-condensable gases in the membrane headspace. Trials and modelling of the process based on known vapour pressures of the gases, ethanol and water, suggest significant efficiency gains in terms of ethanol removal for given surface areas of membranes. 
         [0025]    Efficiency of perstraction can be improved by reducing gas concentrations in the product and strip feeds. 
         [0026]    The strip solution preferably is purified water. The water may be purified by reverse osmosis or particulate and carbon filtration. 
         [0027]    Preferably further, the raw permeate is processed so as to remove oxygen and carbon dioxide and nitrogen therefrom prior to contacting the permeate with the microporous membrane. 
         [0028]    Preferably further, the water also has oxygen, nitrogen and carbon dioxide removed therefrom prior to contacting with the membrane. 
         [0029]    The alcohol in the strip solution is a useful by-product. 
         [0030]    The invention also provides apparatus for reducing the alcohol content of an alcohol containing beverage, the apparatus including: (i) a first processing stage having a reverse osmosis unit or nanofiltration unit having a retentate outlet and permeate outlet; (ii) a pump for supplying beverage to be treated under pressure to the first processing stage whereby retentate is produced at the retentate outlet and raw permeate containing alcohol is produced at the permeate outlet; (iii) a second processing stage which includes at least one hydrophobic microporous membrane, the second processing stage having a first inlet for receiving said raw permeate and a second inlet for receiving a strip solution, the membrane being operable to allow alcohol from the raw permeate to pass therethrough to the strip solution to thereby remove at least a portion of the alcohol from the raw permeate so as to produce dealcoholised permeate at an outlet of the second processing stage; and (iv) means for combining said dealcoholised permeate with said retentate to thereby produce dealcoholised beverage in which the alcoholic content thereof is lower than that of the beverage. 
         [0031]    Preferably, the apparatus includes heater means for heating the strip solution and/or the raw permeate to a temperature in the range from 40° C. to 70° C. and most preferably to a temperature of about 45° C. to 50° C. 
         [0032]    Preferably further, the apparatus includes means for cooling the dealcoholised permeate prior to combining with said retentate. 
         [0033]    The invention also provides dealcoholised beverage when made by the method or apparatus defined above. 
         [0034]    The invention further provides a method for reducing the alcohol content of a wine including (i) processing the wine having a first alcohol concentration by reverse osmosis or nanofiltration to produce a retentate and a raw permeate, the retentate having a second alcohol concentration greater than or equal to the first alcohol concentration, and the raw permeate having a third alcohol concentration less than or equal to the first alcohol concentration; (ii) heating the raw permeate to a temperature in the range of about 40° C. to about 70° C.; (iii) heating strip water to a temperature in the range of about 40° C. to about 70° C.; (iv) after heating the raw permeate, contacting a first side of an hydrophobic microporous membrane with the raw permeate; (v) after heating the strip water, contacting a second side of the hydrophobic microporous membrane with the strip water, extracting alcohol from the raw permeate, and forming a partially dealcoholized permeate having a fourth alcohol concentration at the first side of the hydrophobic microporous membrane; and (vi) combining the retentate with the partially dealcoholized permeate and forming a partially dealcoholized wine having a fifth alcohol concentration less than the first alcohol concentration. 
       DESCRIPTION OF THE DRAWING 
       [0035]    The invention will now be described with reference to the accompanying drawing which is a schematic block diagram of a system for reducing the alcoholic content of wine or other alcoholic beverages. 
     
    
     DETAILED DESCRIPTION 
       [0036]    The diagram schematically illustrates a system  2  for producing reduced alcohol wine in accordance with the invention. The system  2  includes a tank  4  for storage of wine to be treated. Wine from the tank  4  passes to a pump  6  which pumps the wine at high pressure to a reverse osmosis unit  8 . The reverse osmosis unit  8  has membranes therein which pass water and alcohol into the permeate while rejecting other desirable wine aroma, colour and taste components which are retained in the concentrated wine or retentate. The reverse osmosis unit  8  has a permeate outlet  10  and a retentate outlet  12 . The outlet  12  is connected by means of a line  14  to the tank  4  for circulating the reduced alcohol wine. The line  14  includes a back pressure control valve  16  which effectively controls the pressure in the reverse osmosis system  8  and outlet  12 . The membranes in the reverse osmosis unit  8  can typically be in the form of spiral wound reverse osmosis or nanofiltration membranes such as GE Osmonics VinoCon or VinoPro 8040 or 4040. 
         [0037]    Typically the flow of wine through pump  6  is 3,500 to 12,500 litres per hour, depending on type and number of membranes used. 
         [0038]    Typically the temperature and pressure in the reverse osmosis unit  8  and outlet  12  are in the range 13° C. to 25° C. and 1,500 kPa to 7,000 kPa. 
         [0039]    Normally the percentage of wine passing to the retentate outlet  12  will be in the range 80% to 90% of the flow passing through pump  6 . 
         [0040]    Normally the wine in the tank  4  will have an initial alcoholic content in the range from say 13% to 16% by volume. The system of the invention seeks to reduce the alcoholic content of the wine in tank  4  to a more desirable level such as say 12.5% to 13.5%. 
         [0041]    Typically the alcoholic level of the permeate at the raw permeate outlet  10  is 10% to 13% v/v. The flow of permeate leaving the reverse osmosis plant  8  is measured in line  10  by mag flowmeter  194 . Its temperature is measured by temperature probe  196 . Both of these measurements are transmitted to a separate programmable logic controller (not shown) for display and control purposes. 
         [0042]    The system includes a first, second, third or more contactors,  24 ,  26 ,  28  and  30  arranged in a vertical orientation. Contactor  24  removes dissolved gases such as oxygen and carbon dioxide from the flow of stripping water. Contactor  26  degasses the flow of alcoholic permeate. Contactors  28 ,  30 , and possibly others are the alcohol stripping contactors. Each of these can be of the type which includes a hydrophobic microporous membrane, for example of the type Liqui-Cel® Extra-Flow. 
         [0043]    A line  136  is connected from the reverse osmosis outlet  10  so as to pass the raw, unheated permeate to the second contactor  26  to be degassed. 
         [0044]    The system of the invention also includes a vacuum pump  40 , the inlet of which is connected to a vacuum line  42  and includes a non-return valve  188  to prevent service water running back into line  42 . The vacuum line  42  is connected to the second contactor  26  and then to the first contactor  24  by means of a line  46 . The first contactor  24  has an inlet and pressure regulating valve  44  for supplying a counterflow of an inert gas such as nitrogen. Typically the flow of nitrogen is regulated to be about 400 litres per hour. 
         [0045]    Normally the raw permeate is supplied to the shell side of the contactor whereas the vacuum is applied to the lumen side or the interior of the multiplicity of membrane tubes which pass through the contactors  24  and  26 . The vacuum has the effect of removing carbon dioxide and oxygen from the stream of warm stripping water in contactor  24  and from the stream of raw permeate in contactor  26 . 
         [0046]    The system of the invention includes a heat exchanger  18  which warms the degassed permeate by counterflow heat exchange with the hot treated permeate returning in line  62 . The contactor  26  is connected to the heat exchanger  18  by line  34 . A line  36  is connected to the heat exchanger  18  so as to pass the degassed, pre-warmed permeate to another heat exchanger  22  which heats the permeate further by counterflow heat exchange with heated strip water. A line  48  passes the heated, degassed permeate from heat exchanger  22  to the bottom, shell side inlet of the alcohol stripping contactors  28  and  30 . 
         [0047]    The tops of contactors  28  and  30  receive a flow of degassed strip water on input line  150  from the degassing contactor  24 . The alcohol stripping action takes place in the contactors  28  and  30  where the heated, degassed permeate encounters a counterflow of heated, degassed strip water and its alcohol concentration is typically reduced to 3% to 6% v/v. 
         [0048]    Stripping contactors  28  and  30  are arranged in a parallel configuration so that the stream of degassed permeate entering from line  48  is split to line  50  before flowing upwards through contactor  28  and through line  52  to the bottom of contactor  30 . Valves  51  and  53  allow contactors  28  and  30  to be isolated from the system. The hot, alcohol reduced permeate passes from contactor  28  via line  56  to a flow control valve  58  then to a flow monitoring rotameter  60  to line  62 . A similar line  64 , flow control valve  66  and flow monitoring rotameter  68  pass the alcohol reduced permeate from contactor  30  to line  62 . A pressure transmitter  70  monitors the back pressure in the permeate lines  48 ,  50  and  52  and transmits its measurement to a separate controller (not shown) for display and control purposes. 
         [0049]    The relative flows of permeate through the two contactors  28  and  30  and the pressure as measured by pressure transmitter  70  are controlled by the flow control valves  58  and  66 . 
         [0050]    The still hot reduced alcohol permeate then passes through line  62  to heat exchanger  18  where it is cooled by, and in turn pre-warms the raw, degassed permeate coming from the contactor  26  via line  34 . The treated and cooled permeate from heat exchanger  18  then passes through line  72  and non return valve  74  to be mixed with the concentrated wine (retentate) in line  14  for return to tank  4 . The wine returning to tank  4  therefore has a reduced alcoholic content measured by volume which is typically 0.5% to 1.5% lower than the untreated wine in tank  4 . The flow rate of reduced alcohol permeate is measured by flowmeter  190  and its temperature is measured by temperature probe  192 . 
         [0051]    By comparing the temperature corrected flows in lines  10  and  72 , the difference in flows correlate with the rate of alcohol removed and so provides a means of monitoring and controlling the performance of the alcohol reduction process. 
         [0052]    In accordance with the invention, the alcohol stripping is carried out on the permeate rather than the wine itself and therefore desirable volatile components in the wine remain substantially unchanged because they remain in the retentate. 
         [0053]    The system includes a source of water  76  which supplies water via inlet line  78  to a pressure pump  80 . Preferably the water has been purified say by reverse osmosis prior to admission to the supply source  76 . However, where water quality permits, this could be a mains supply. Pump  80  supplies water under pressure via line  82  to a break tank  84  which includes a float valve  86  to maintain a constant level of service or seal water for vacuum pump  40 . Break tank  84  includes a line  88  and valve  90  to drain the tank to refuse point  92 . 
         [0054]    Pressure pump  80  also supplies water via line  94  to surge tank  98 . Maximum flow to this tank is regulated by valve  96  and level in the tank is maintained by float valve  100 . An overflow line  102  passes any excess to drain point  104 . A drain line  186  with valve  184 , allows the surge tank  98  to be drained to point  92  (or  104  if more convenient). 
         [0055]    Water in the surge tank  98  then passes via line  106  to a pump  108 , then on to a combined particulate and adsorbent carbon filter  112 . Differential pressure across this filter is monitored by pressure gauges  116  and  118 . The purpose of this filter is to remove any large solids in the water which could foul the membrane contactors and any taints which could pass the membranes; taint the permeate and then the wine. 
         [0056]    After filter  112 , the water passes through line  122  to heat exchanger  126 . Flow in line  122  is monitored by flow detector switch  124  which sends a signal to a separate controller in the event of no flow in the line. The water from line  122  is pre-warmed in heat exchanger  126  by a counter flow of hot, alcoholic strip water returning from the stripping contactors via line  128 . The cooled alcoholic strip water leaves heat exchanger  126  for recovery or disposal to waste via line  142 . The flow of alcoholic strip water by product in line  142  is measured by a flow totaliser  146 . 
         [0057]    The pre-warmed raw strip water from heat exchanger  126  then passes through line  130  to heater  132  where it is heated to approximately 65° C. to 75° C. Heater  132  could be of whatever type—gas, electric element or heat pump—which is most appropriate for the site and the duty. 
         [0058]    The heated strip water then passes through line  134  to heat exchanger  22  where it heats the pre-warmed, degassed permeate entering in counter flow from line  36 . The heated strip water then passes through line  38  to contactor  24  for degassing. The temperature of the heated strip water in line  38  is monitored by temperature transmitter  140  which sends an analogue signal to a separate controller. The temperature of the heated permeate in line  48  is also monitored by a temperature transmitter  138 . Heat exchanger  22  is sized so that the counter flows of permeate and strip water both leave heat exchanger  22  at approximately 45° C. to 55° C. 
         [0059]    After heating in heat exchanger  22  and passing through line  38 , the heated, degassed alcoholic strip water leaves contactor  24  via manifold line  150  to the tops of stripping contactors  28  and  30 . A flow control needle valve  110  adjusts the overall flow of strip water and the pressure in line  150  as measured at pressure transmitter  160 . Isolation valves  152  and  154  are used to control the flow of water to the tops of the contactors  28  and  30 . Preferably flow would be arranged so that stripping water flows through the two contactors  28  and  30  in parallel. 
         [0060]    Preferably the pressure as measured at transmitter  160  on line  150  should be lower than the pressure in the permeate line  48  as measured at transmitter  70 . The flow rates in each of lines  172  and  174  are monitored by rotameters  176  and  178  respectively and are controlled by the degree of opening of valves  152  and  154 . 
         [0061]    It has been found that the efficiency of alcohol extraction in the stripping contactors  28  and  30  is improved if both the permeate and the strip solution have carbon dioxide and oxygen removed therefrom. As described previously, vacuum pump  40  draws a vacuum on lines  42 ,  44  and  46  and on the lumen side of contactors  24  and  26 . Typically the pressure in the line  42  as measured by pressure transmitter  180  is −80 kPa to −95 kPa. 
         [0062]    The system is arranged such that water from break tank  84  maintains a supply of service (sealing and cooling) water to vacuum pump  40 . The exhaust gases and service water which are ejected by the vacuum pump pass through line  182  to surge tank  98  where the gases including the nitrogen strip gas from line  44  and the carbon dioxide and oxygen extracted from contactors  24  and  26  are expelled to the atmosphere. Some minor amounts of alcohol from the permeate in contactor  26  are also expelled. The water from line  182  is then available to be used for stripping purposes, so minimising the use of water by the system. 
         [0063]    Many modifications will be apparent to those skilled in the art without departing from the spirit and scope of the invention.