GB2140455A - Purification of beverages - Google Patents

Abstract

Beverages such as whisky or beer containing nitrosamines including N-nitro-sodimethylamine (NDMA) are treated so as to reduce the NDMA content thereof by exposing the beverage to ultra-violet radiation having a wavelength such as to decompose the NDMA, preferably in the range 330 to 380nm, whilst preventing the beverage being exposed to radiation having wavelengths below 300 nm preferably by passing the radiation through a filter such as to cut out such wavelengths below 300 nm. Apparatus for carrying out the method may be mounted in steel wall 10 of a reaction vessel and comprises mercury vapour lamp 20 with quartz discharge tube 22. Four flat filter glasses (55) are mounted in slots located in four rods 45. Mole 60 accommodates tube 65 and whisky flows around the outside of this tube, thus being irradiated through 360 DEG around the radiation source. <IMAGE>

Description

SPECIFICATION Purification of beverages The present invention relates to the purification of beverages in particular the removal of nitrosamines from beverages produced from malted cereals e.g. barley such as beer and to a much more critical extent whisky especially single malt whiskys.

Certain techniques for malting barley in particular the use of North Sea gas rather than heavy fuel oils for heating malting kilns, whilst attractive for some reasons, have produced increased N-nitrosamine levels in beverages produced from such malts.

N-nitrosamines have been indited as carcinogens and the major N-nitrosamine found is N-nitrosodimethylamine (herein NDMA) which can occur at levels as high as 100 parts per billion (100,000,000) (P.P.B.). It is desirable to reduce the NDMA content e.g. to no more than 5 P.P.B in the whisky as sold (i.e. as 40% alcohol).

It has been known since 1971 that N-nitroso compounds can be photochemically destroyed by light and much work was done but this revealed that many other compounds in the whisky in particular the flavour compounds or congenors were also destroyed and most workers gave up at this stage.

We continued our investigations and tried many possible routes which at best only produced slight reductions in levels of N-nitroso compounds and which would have been difficult to carry out in practice, bearing in mind the Customs and Revenue aspects of the production process in effect requiring it to be a sealed process so that the Revenue can be sure that the correct duty on production has been paid.These methods were: interaction with various metal ions, of the several tried, only tin and copper showed a slight interaction, but this was not thought significant; among free metals tested gold and zinc showed slight effects, but these were not thought significant; reactive oxides such as lead dioxide which might oxidise the NDMA showed no reaction; absorption with insoluble substances incorporating metal ions was tried but no large effects were found, only ferrous sulphide and magnesia showed any reduction but this was very slight; absorbants such as carbon, pectin and nylon were examined and only carbon had a very slight effect, although carbon was thought of as having some potential the massive removal of flavour which it produced ruled this out; some esters of long chain fatty acids were added to whisky to study whether the nitrosamines might be precipitated with these on chilling, no reduction was noted; various proteins such as albumin, haemoglobin and casein were added, but no reduction in N-nitrosamine levels took place; various other techniques such as ion exchange and membrane filtration were examined, although these showed some promise in removal of N-nitrosamines, they also removed most of the whisky flavour.

Thus despite the abandonment of the earlier efforts to use light to remove NDMA we returned to this route.

After exhaustive testing of different wavelengths we found that there were wavelengths at which NDMA was destroyed although not efficiently in terms of energy input but at certain wavelengths flavour loss was not significant commerciall. We also found that it was possible to produce irradiation devices from relatively cheap light sources producing as part of their spectrum the desired wavelengths and to effectively filter out the damaging parts of their spectrum without attenuating significantly their NDMA destroying wavelengths.

According to the present invention a method of purifying beverages containing N-nitrosamines including NDMA so as to reduce the NDMA content thereof comprises exposing the said beverage to ultraviolet radiation having a wavelength such as to decompose the NDMA whilst preventing the beverage being exposed to radiation having wavelengths below 300 nm. This invention is particularly applicable to whisky, which has an acid pH.

The source of UV radiation desirably has an emulsion peak in the range 330 to 380 nm and is preferably a mercury vapour lamp. These have an emission peak in the range 330 to 380 nm and the radiation therefrom is passed through a filter such that substantially none of the said UV radiation having a wavelength below 300 nm reaches the beverage.

The filter is desirably one which is such as to transmit no more than 20% at wavelengths below 320 nm.

The filter desirably is such as to transmit at least 50% at wavelengths between 360 and 380 nm.

The mercury vapour lamp is preferably arranged to have the UV emitter immersed in the beverage and to be surrounded by the filter or filters.

The emitter is desirably of cylindrical form, as this conveniently provides a large area from which the UV radiation is emitted.

The invention also extends to apparatus for carrying out the method of the invention comprising a source of UV radiation having a wavelength such as to decompose NDMA, means for diffusing the said radiation through the beverage and means for preventing the beverage being exposed to UV radiation having wavelengths below 300 nm.

In a preferred form of the apparatus the source of UV radiation is a mercury vapour lamp, the means for difussing the said radiation through the beverage comprise a tubular extension of the lamp or the lamp being of tubular form mounted for location in the beverage so as to radiate outwardly in substantially unimpeded manner and the means for preventing the beverage being exposed to radiation having wavelengths below 300 nm comprise a filter or filters surrounding the said lamp or tubular extension.

The envelope of the lamp or tubular extension thereof is preferably surrounded by a further envelope spaced therefrom and means are provided for circulating coolant, e.g. coolant water, therebetween.

There is preferably also an outer envelope within which the lamp or tubular extension is located, the filters being located between the outer envelope and the lamp or the further envelope surrounding the lamp.

The filters are preferably flat sheets located in supports so as to surround the lamp or tubular extension.

The UV lamp is conveniently mounted on a flange adapted to be secured over an aperture in a treatment vessel with the lamp or tubular extension extending through the hole into the vessel, the flange also supporting a biassed clamping mechanism adapted to engage the upper end of the outer envelope and operable from outside the treatment vessel so as to draw the upper end of the outer envelope into sealing engagement with the inner face of the flange.

The UV lamp may be mounted on an outer wall flange, which supports the further envelope, and the outer wall flange may in turn be mounted on a subflange which may be mounted on the flange.

The subflange conveniently carries mounting means for the filter or filters.

The mounting means may comprise rods extending parailel to the lamp or tubular extension and provided with opposed slots in which the edges of the filter sheets are nested.

The filters preferably are such as to have substantially zero transmission of wavelength less than 300 nm and to have at least 50% transmission of wavelengths between 360 and 380 nm.

The invention may be put into practice in various ways and one specific embodiment will be described to illustrate the invention with reference to the accompanying drawings in which: Figure 1 is a vertical cross-section of part of an irradiation apparatus incorporating UV filters in accordance with the present invention; Figure 2 is a cross-section on the line ll-ll of Figure 1 showing a quarter of the total cross-section with the components in Figure 2 aligned with the same components in Figure 1; Figure 3 is a cross-section on the line ll-ll of Figure 1 showing half of the total cross-section and rotated through 90D relative to Figure 1 and 45" relative to Figure 2;; Figures 4 and 5 are gas chromatograms of whisky samples originally containing NDMA, Figure 4 being of the whisky before UV irradiation and Figure 5 being of the whisky after UV irradiation using a mercury vapour lamp without the use of filters; Figure 6 is a graph showing the UV spectrum of a mercury vapour lamp used to produce the material shown in Figure 5; Figure 7 is a graph showing the UV absorbance with varying UV wavelengths of a 5 year old single malt whisky and NDMA. and Figures 8 and 9 are graphs showing % transmission at 1 mm thickness against UV wavelength for four filter glasses appropriate for use in the present invention.

To recap, the invention makes use of the sensitivity to photolysis of N-nitrosamines which occur in whisky and other beverages derived from malted barley. However, damage to flavour constituents is avoided or minimised by using a selected wavelength range which although not the most efficient for the photolysis of N-nitrosamines avoids damage to the flavour and using filters to filter out all but the selected radiation.

The apparatus thus relies on a filtered UV radiation source which is mounted in a hole 60 in the wall of a reaction vessel; referring to Figure 1 the wall of this is shown at 10 and conveniently is of stainless steel.

The radiation source 20 consists of a 12 Kw high pressure mercury vapour arc lamp e.g. a CANRAD HANOVIA lamp; the quartz discharge tube 22 of which extends into the reaction vessel but is protected from the contents thereof by an outer quartz tube 23, provision 24 being made for cooling water to be circulated through the space between these tubes. The tubes 22 and 23 are each 3 mm thick. The upper end 25 of the outerwall tube 23 diverges and is supported via a gasket 28 on a mating inclined annularface 26 of an outer wall flange 27.

The housing 36 of the arc lamp is mounted via a base flange 37 and screws 38 on the outer wall flange 27.

This flange is itself mounted via screws 29 and a gasket 30 on a subflange 35. The subflange is in turn nested in an annular recess 40 of a main support flange 50 via a gasket 41 and secured therein by screws 42.

The subflanges in addition carries four filter mounting rods 45 located at the corner of a square externally of the outer quartz tube 23. These rods are made of aluminium alloy e.g. DURAL, their cross sections are shown in Figure 3; each rod is secured to the subflange by a screw 46. Four flat filter glasses 55 e.g. of Schott type WG 345 filter glass (details of the transmission chracteristics of which are given in Figure 9) are mounted in opposed slots located in the rods 45. The tubes 22 and 23 are round bottomed and the filters 55 extend below the ends of the tubes e.g. by at least the diameter of the inner tube and there is a non-transmitting plug e.g. of DURAL closing off the bottom of the filter space or a sheet of the filter glass may extend across below the inner tubes.

The main support flange 50 is secured by bolts 62 over the hole 60 in the wall of the reaction vessel, gaskets 61 being interposed between the lower face of the flange 50 and the outside of the vessel 10. The hole 60 is made large enough to accommodate not only the tubes 22 and 23 and rods 45 but also an outer tube 65 which has a divergent and thickened neck 66. The tube 65 is made of borosilicate glass supplied by Corning, its transmittance values are shown in Figure 10. The outer face of the neck 66 is engaged by a mating flange 70 which is connected to the main support flange by a spring loaded bolts 71 which can be tightened from outside the reaction vessel so as to draw the tube 65 upwardly so that its top end face 67 can sealingly engage the bottom face of the flange 50 via a gasket 73.

The whisky flows around the outside of the tube 60 thus being irradiated through 360" around the UV radiation source. The tube 65 is 87 inches (221 cm) long and 16.5 cms in diameter and is designed to treat 2500 litres in 7-8 hours.

A smaller experimental system to the same design concept could treat 5 litres of whisky of about 63% alcohol content of medium depth of colour having an absorbance of 0.05 at 525 nm blanked against water, in 7-8 hours to reduce an initial 30 P.P.B. of NDMA to 10 P.P.B.

We have found the amount of energy input required varies with the colour of the beverage, the darker the more energy is required. For an average coloured whisky we have found that about 850 to 870 milliwatts will produce a 50% reduction of NDMA level in 1 litre of whisky. Thus an energy input in the range 700 to 1000 milliwatts seems likely to be appropriate for most whiskys to achieve the same results.

Figures 4 and 5 are gas chromatograms of such a typical sample of whisky having an acid pH due to presence of acids such as acetic acid before treatment and the same sample treated without the use of filters.

When the filters were used the chromatogram was indistinguishable from that shown in Figure 4. Figure 12 shows the UV absorption spectra for the whisky before treatment (curve 90) and after treatment (curve 91) using a 60% ethanol water blank.

The values of certain of the peaks are shown in Table I below.

TABLE I Figure Time C') Name of compound 4 4.13 0.8664 Methylacetate 5 4.12 0.4473 Methylacetate 4 5 4.39 0.2821 Methyl acetate 4 5.74 52.9608 Ethyl acetate 5 5.79 55.2784 Ethyl acetate 4 9.84 44.4437 N-propanol 5 9.86 32.9560 N-propanol 4 11.48 73.5150 Isobutanol 5 11.47 72.8446 Isobutanol 4 12.41 3.4818 Isoamyl acetate 5 12.42 3.3188 Isoamyl acetate 4 13.33 1.0537 N-butanol 5 13.34 1.0093 N-butanol 4 15.13 145.4652 Isoamyl alcohol 5 15.11 143.7005 Isoamyl alcohol 4 16.09 0.1197 Pentan-l-ol 16.07 0.0879 Pentan-l-ol 4 16.42 5.4145 Pentan-l-ol 5 16.42 5.4145 Pentan-l-ol 4 19.46 1.7853 Ethyl lactate 5 19.45 1.6176 Ethyl lactate 4 22.16 2.8199 Ethyl capylate 5 22.15 2.8342 Ethyl capylate 4 23.22 5.9399 Furfural 5 23.26 0.2729 Furfural 4 27.69 13.4057 Ethyl caprate 5 27.67 10.8771 Ethyl caprate 4 32.38 0.4122 Phenylethyl acetate 5 32.35 0.2735 Phenylethyl acetate 4 32.71 5.4966 Ethyl laurate 5 32.69 5.1184 Ethyl laurate 4 33.23 0.9497 Isoamyl caprate 5 33.22 0.6488 Isoamyl caprate 34.42 4.2992 2-Phenyl ethanol 5 34.90 3.1427 2-Phenyl ethanol 4 38.59 1.0991 Ethyl myristate 5 38.60 1.0053 Ethyl myristate 4 48.36 4.1553 Ethyl palmitate 5 48.38 3.2480 Ethyl palmitate 4 Ethyl palmitoleate 5 50.17 1.1869 Ethyl palmitoleate 4 56.28 2.4497 Ethyl oleate 5 56.35 1.1931 Ethyl oleate Notes on Table!: 1) C means concentration in grams/100 litres of absolute alcohol.

Figure 7 is a graph showing an ultraviolet absorption spectrumof a typical five year old whisky (curve 80) and of NDMA (curve 81) showing absorbance at different wavelengths which we prepared by providing narrow wavelength band widths of UV radiation and exposing samples of the same material successively to these different wavelength bands and measuring the absorbance. The wavelength bands had a spread of +10 nm i.e. the 320 nm band was 320 t 10 nm. Figure 11 is a similar graph for NDMA in absolute ethanol.

It will be observed that a substantial proportion of the NDMA absorption occurs at wavelengths where very little absorption by the whisky sample is occuring.

However as can be seen from Figure 6 which is a spectrum for a mercury vapour lamp such lamps produce substantial emissions also in regions below 300 nm were the major absorbance by the whisky sample occurred.

We thus use a mercury vapour lamp but filter it's UV radiation emission so as tocut out or very severely attenuate emissions with wavelengths below 340 nm particularly below 320 and most preferably cutout all emissions below 300 nm.

Figure 6 shows that the mercury vapour lamp has a peak at 365 nm and we have found this to be effective in destroying NDMA without unacceptably altering whisky flavours.

In order to achieve rapid treatment of large volumes of beverage it is necessary for the light to be diffused or to radiate outwardly in substantially uninterrupted manner and the apparatus described above achieves this.

We have carried out careful tests of a range of filter glasses to find ones appropriate to our needs.

We have found that Schott filter glasses WG 345, WG 360 and GG 375 (curves 85, 88 and 86 in Figure 8) are effective as is Corning PYREX 7720 (curve 87 in Figure 9). Corning PYREX 7720 is a lime glass.

It will be noted that all four glasses shown have essentially zero transmittance (at 1 mm thickness) at wavelengths below 300 nm and less than 20% transmittance (at 1 mm thickness ) at 320 nm, but also have a transmittance (at 1 mm thickness) in excess of 50% at 360 nm and in fact of in excess of 70% at 360 nm for curves 85,88 and 87. These filters are used at 1 mm thickness.

Clearly a monochromatic source of UV radiation in the range 320 to 380 nm would avoid the need for filters. Such devices as UV lasers are conceptually appropriate but their current very high cost and their intrinsic power and thus danger render them unattractive for the use we have in mind. Problems might also be entailed in ensuring that the radiation was sufficiently diffused to treat large volumes of liquid rapidly and economically.

Thus whilst in the current state of technology we prefer to use a mercury vapour lamp as the UV source we do not exclude the possibility of our invention being practiced by use of such monochromatic sources.

Claims (19)

1. A method of purifying beverages containing nitrosamines including NDMA so as to reduce the NDMA content thereof which comprises exposing the said beverage to ultraviolet radiation having a wavelength suhch as to decompose the NDMA whilst preventing the beverage being exposed to radiation having wavelengths below 300 nm.

2. A method as claimed in Claim 1 in which the beverage is whisky.

3. A method as claimed in Claim 1 or Claim 2 in which the source of UV radiation has an emission peak in the range 330 to 380 nm and the radiation therefrom is passed through a filter such that substantially none of the said UV radiation having a wavelength below 300 nm reaches the beverage.

4. A method as claimed in Claim 1,2 or 3 in which the UV radiation is provided by a mercury vapour lamp.

5. A method as claimed in Claim 3 in which the filter is such as to transmit no more than 20% at wavelengths below 320 nm.

6. A method as claimed in Claim 4 or Claim 5 in which the filter is such as to transmit at least 50% at wavelengths between 360 and 380 nm.

7. A method as claimed in Claim 4,5 or 6 in which the mercury vapour lamp is arranged to have the UV emitter immersed in the beverage and to be surrounded by the filter or filters.

8. A method as claimed Claim 7 in which the emitter is of cylindrical form.

9. Apparatus for carrying out the method of Claim 1 comprising a source of UV radiation having a wavelength such as to decompose NDMA, means for diffusing the said radiation through the beverage and means for preventing the beverage being exposed to radiation having wavelengths below 300 nm.

10. Apparatus as claimed in Claim 9 in which the source of UV radiation is a mercury vapour lamp, the means for diffusing the said radiation through the beverage comprise a tubular extension of the lamp orthe lamop being of tubular form mounted for location in the beverage so as to radiate outwardly in substantially unimpeded manner and the means for preventing the beverage being exposed to radiation having wavelengths below 300 nm comprise a filter or filters surrounding the said tubular extension.

11. Apparatus as claimed in Claim 10 in which the envelope of the lamp or tubular extension thereof is surrounded by a further envelope spaced therefrom and means are provided for circulating coolant therebetween.

12. Apparatus as claimed in Claim 10 or Claim 11 in which there is an outer envelope within which the lamp or tubular extension is located the filters being located between the outer envelope and the lamp or the further envelope surrounding the lamp.

13. Apparatus as claimed in Claim 12 in which the filters are flat sheets located in supports so as to surround the lamp or tubular extension.

14. Apparatus as claimed in any one of Claims 10 to 13 in which the UV lamp is mounted on a flange adapted to be secured over an aperture in a treatment vessel with the lamp or tubular extension extending through the hole into the vessel, the flange also supporting a biassed clamping mechanism adapted to engage the upper end of the outer envelope and operable from outside the treatment vessel so as to draw the upper end of the outer envelope into sealing engagement with the inner face of the flange.

15. Apparatus as claimed in Claim 14 in which the UV lamp is mounted on an outer wall flange, which supports the further envelope, and the outer wall flange in turn is mounted on a subflange which is mounted on the flange.

16. Apparatus as claimed in Claim 15 in which the subflange carries mounting means for the filters.

17. Apparatus as claimed in Claim 16 in which the mounting means comprise rods extending parallel to the lamp or tubular extension and provided with opposed slots in which the edges of the filter sheets are nested.

18. Apparatus as claimed in any one of Claims 9 to 17 in which the filters are glass filters such as to have substantially zero transmission of wavelengths less than 300 nm and to have at least 50% transmission of wavelengths between 360 and 380 nm.

19. Apparatus as claimed in Claim 9 substantially as specifically described herein with reference to Figures 1,2 and 3 of the accompanying drawings.