WO2018033649A1

WO2018033649A1 - Method for smoking e-liquids and device therefor

Info

Publication number: WO2018033649A1
Application number: PCT/EP2017/071059
Authority: WO
Inventors: Huw David Griffiths; Elena CRISTEA
Original assignee: Puresmoke Limited
Priority date: 2016-08-19
Filing date: 2017-08-21
Publication date: 2018-02-22

Abstract

A method of treating an e-liquid solution to make a smoked e-liquid, comprises: (i) providing a source of smoke that has optionally been filtered to reduce its PAH content, (ii) providing a smoking vessel (e.g. pan) containing the solution, and (iii) introducing bubbles of smoke into the solution at a mixing head of a mixer and no more than 3cm from a blade of the mixer, while agitating the solution with the mixer blade so as to break up the introduced smoke into a plurality of bubbles of average diameter 2mm or less, (iv) venting the smoking vessel to the atmosphere, and (v) cooling the solution so as to maintain it at a temperature of 30°C or below.

Description

Method for Smoking e-Liquids and Device Therefor

Introduction

The present invention relates to a method for smoking liquids and to a device therefor, especially to methods for smoking liquids for use in e-cigarettes. Apparatus to carry out the smoking methods are also provided.

Background to the Invention

Prior art water smoking methods are known, using large trays of water in a static smoking chamber, the water becoming slowly infused by smoke over a number of days, typically about 3-4. "Smoked water" is a commercially available product in the food industry.

Another known prior art process produces concentrated smoke condensate by condensing water vapour in a smoking tower, usually coated with tar by long term exposure to smoke. This condensate is then diluted by the customer according to its end use; it normally produces a bitter and/or acrid taste. "Liquid smoke", much more concentrated than smoked water, is also commercially available in this industry. There are other non-commercial methods of making "liquid smoke". One example involves collecting the smoke condensate in a bowl placed on top of a chimney using ice.

US 2012/0207898 describes a hermetically sealed system and related method for smoking liquids. Smoke is produced and re-circulated in limited supply, in an attempt to conserve fuel. The smoke inside the system is cooled, in order to promote mixing of the smoke into the liquid. As smoke is produced by burning of fuel, the pressure in the system starts to increase. This method therefore requires specialist equipment to cope with the increased pressure in the system. A valve and a limited air supply are present, in order to avoid the pressure in the system from rising to levels that the equipment is not suitable to handle. Nevertheless, the pressurised system is more dangerous than conventional smoking methods, e.g. using water trays. As an alternative to cigarettes, e-cigarettes are nowadays popular and use a liquid (an "e-liquid") that is converted into a vapour or aerosol and inhaled by a user. The e-liquid generally contains a solution of nicotine in water and/or propylene glycol and/or glycerol. Currently there are no smoked e-liquids on the market. Tobacco flavoured e-liquids are known, as are combinations of tobacco with other flavours. These e-liquids are synthetically made, and it is also known to extract the flavour directly from tobacco and add this to e-liquids.

The known smoking methods typically require long production times.

Separately, tobacco-flavoured e-liquids are found by some a poor substitute for the flavour and feel of smoke.

It is an object of the invention to provide alternative methods of smoking liquids, and methods of smoking carried out on alternative liquids. Preferred embodiments of the invention aim to provide improved smoking methods, apparatus therefor and products obtained thereby. Specific embodiments of the invention provide smoking methods with reduced operating times and/or improved outputs. An additional object of the present invention is to provide a fast, reliable and safe smoking method under atmospheric pressure.

Summary of the Invention

The inventors of the present invention have found that various solutions can be smoked with improved efficiency, whether to make smoked water or a product more like liquid smoke (i.e. much more concentrated) and that such smoking methods can be applied to previously unsmoked liquids, in this case e-liquids.

Herein, the terms e-liquid and e-liquid solution refer to such liquids for e-cigarettes and containing one or more humectants, usually propylene glycol or glycerol (also called glycerine) or both, and wherein one or more flavouring(s) are usually included and nicotine is optional. In this context, smoked water or brine for flavouring food is not an e-liquid. Accordingly, in a first aspect of the invention there is provided a method of treating an e-liquid solution, comprising:

(i) providing a source of smoke,

(ii) providing a smoking vessel (e.g. pan) containing the solution, and

(iii) introducing the smoke into the solution in the form of fine bubbles, preferably while agitating the solution so as to mix its contents.

This aspect of the invention typically provides a method of treating an e-liquid solution, comprising:

(iv) providing a source of smoke,

(v) providing a smoking vessel (e.g. pan) containing the solution, and

(vi) introducing bubbles of smoke into the solution while agitating the solution so as to break up the introduced smoke into a plurality of smaller bubbles. The methods are especially useful for making smoked e-liquids. The solution that is smoked may comprise water and/or humectants such as propylene glycol and glycerol, and optional other components. These form the base for liquids that carry nicotine (when present) and flavourings (when present) in liquids used in electronic cigarettes - referred to herein as e-liquids. The base may just require to be packaged or it may require dilution or flavouring subsequently. Typically, the base comprises propylene glycol and/or glycerol. Apart from the base for e-liquids, the solution may also contain other optional flavourings, e.g. spices, botanicals; the choice of these does not form part of the invention.

It is preferred that the methods comprise filtering the smoke to reduce its PAH content.

The invention provides new products, including smoked e-liquids made by a method of the invention.

The invention similarly provides apparatus for treating an e-liquid solution comprising:

a smoke chamber having an air input and a smoke output and in which fuel can be combusted to generate smoke; a smoking vessel (e.g. pan) capable of holding the solution to be treated; a mixer for mixing contents of the smoking vessel; and

a conduit from the output of the smoke chamber to the smoking vessel with an exit for introducing the smoke into the solution, below the surface of the solution; wherein the apparatus is adapted to break up the introduced smoke into bubbles.

Again, preferred apparatus uses or comprises a PAH filter for filtering the smoke before it is introduced into the solution. Preferably, the mixer is adapted to agitate the solution and bubbles so as to break up the introduced smoke into a plurality of bubbles.

In preferred apparatus, the vessel is charged with the e-liquid to be treated. In addition to improving smoking time, the methods and apparatus can increase the interaction between smoke aromatics and molecules of the e-liquid solution (due to fine bubbles produced) resulting in a more complex flavour profile.

Details of the Invention

Methods of the invention treat an e-liquid solution by:

(i) providing a source of smoke,

(ii) providing a smoking vessel (e.g. pan) containing the solution, and

(iii) introducing bubbles of smoke into the solution, preferably while agitating the solution so as to break up the introduced smoke into a plurality of smaller bubbles.

Solutions to be smoked may be e-liquid bases and may comprise one or more flavours. Such flavours can be added after smoking. Methods of the invention also include smoking flavoured solutions, and still further include smoking these while mixing with flavourings introduced into the smoking vessel.

Methods may comprise introducing smoke bubbles using an aerator, dividing the smoke from the chamber into smaller bubbles dispersed into the solution. An airstone or aspirator may be used. Preferred methods introduce bubbles, break them up and mix the vessel contents.

Preferably the smoking comprises filtering the smoke to reduce its PAH content, e.g. treating the smoke to selectively remove therefrom one or more PAHs that contain 4 or more benzene rings. In further preferred embodiments, the subject of examples below, filtration is applied to selectively remove benzo(a)pyrene, benz(a)anthracene and/or dibenz(a,h)anthracene from the smoke. Smoke can be filtered by generating smoke in the presence of filter material and/or passing smoke through a filter. Suitably, fuel and filter material are both present in the chamber that provides the smoke source, and fuel is combusted in the presence of the filter, being intimately mixed therewith. This approach was used in the examples below.

Thus in preferred methods herein, the treating comprises removing one or more PAHs from the smoke using a filter. For example, the level of PAH is reduced by passing the smoke through a filter or directly contacting fuel with the filter. The filter may be a natural or synthetic porous mineral. In particular, the mineral may be a zeolite. In a particularly preferred embodiment, the zeolite is clinoptilolite. Typically, for a filter separate from the fuel, filter material in the form of powder or granules is packed into and retained in or on a filter holder such as a box or column. In preparation of filters for use in the invention, the filter material may also be combined with other components, e.g. with support material, and/or with sand or iron salts.

Suitable filters remove from the smoke PAHs containing 4, 5 or more benzene rings, thus removing PAHs such as pyrene, benz(a)anthracene, naphthacene, chrysene, benzo(a)pyrene and dibenz(a,h)anthracene. Other suitable filters also remove PAHs containing 3 or more rings, thus removing PAHs such as anthracene, phenanthrene and 2-methyl anthracene. Still further suitable filters may be used to also remove PAHs having just 2 rings. As will be appreciated, PAH size is related to but not directly proportional to the number of rings and a size exclusion filter that removes PAHs having 2 rings will also remove larger PAHs e.g. having 3, 4, 5 or more rings.

Pre-treatment of the filter may be employed to modify and preferably improve its properties and/or activity. The filter can be pre-treated by soaking in mild acid, preferably containing ammonium ions, suitably ammonium chloride. For example, the filter may be soaked in approximately 1 molar ammonium chloride, for instance for approximately 24 hours prior to use. Generally, the filter is dried prior to use.

A separate, also optional, though related step is to treat the filter by ion exchange so as to exchange sodium and/or calcium ions, e.g. in the zeolite, preferably clinoptilolite, with lithium, potassium or preferably ammonium ions. The filter can be treated with KOH, KCI, LiOH, LiCI or ammonium ions for this purpose, e.g. using ammonium chloride as described above and in more detail in specific embodiments below. Again, the filter material is generally dried prior to use.

A further separate, also optional but preferred, step is to heat the zeolite filters prior to or during use. Heat treatment assists filter performance, it is believed by opening channels in the filter material e.g. by removing water, and can be for an hour or more, a few hours or up to about 12 hours. An embodiment of the invention comprises pre-treating the filter by heating or baking at 150°C or higher, preferably 200°C or higher, typically at around 270°C or more. Baking / heating activates the filter in that it is better able to remove PAHs from smoke. The filter may also be baked / heated between batches of smoke treatment to re-activate the filter.

Suitably, the treating comprises filtering the smoke selectively to remove one or more PAHs that contain 3 or more benzene rings. Preferably, the treating comprises filtering the smoke selectively to remove one or more PAHs that contain 4 or more benzene rings. Typically, the method removes a plurality of the PAH compounds and in specific embodiments of the invention removal of substantially all of a large number of PAHs has been achieved. In embodiments of the invention, the one or more PAHs are selected from benzo(a)pyrene, benz(a)anthracene, benzo(b)fluoranthene, benzo(j)fluoranthene, benzo(k)fluoranthene, benzo(g,h,i)perylene, chrysene, cyclopenta(c,d)pyrene, dibenz(a,h)anthracene, dibenzo(a,e)pyrene, dibenzo(a,h)pyrene, dibenzo(a,i)pyrene, dibenzo(a,l)pyrene, indeno(1 ,2,3-cd)pyrene, benzo-(c)-fluorene or 5-methylchrysene. The method removes significant quantities of one or more of the PAHs, and preferably removes significant quantities of a plurality of the PAHs. In specific examples, described below, particular PAHs known to be carcinogenic are substantially removed but the smokey flavour is substantially unimpaired. Methods of the invention may thus comprise selectively removing the PAHs benzo(a)pyrene, benz(a)anthracene, dibenz(a,h)anthracene, two of those PAHs or all three. In particularly preferred embodiments, the method reduces the level of at least benzo(a)pyrene and/or benz(a)anthracene.

The agitation preferably breaks up the smoke into fine / tiny bubbles, promoting rapid dissolution of its contents. The agitation also mixes the smoke bubbles with and into the solution. Suitably the methods comprise breaking the smoke into bubbles of average diameter 10mm or less, 5mm or less, preferably 2mm or less, preferably 1 mm or less, 0.5mm or less and even smaller. The apparatus used may comprise a mixer having a mixing head immersed in the solution. Methods can then comprise introducing the smoke into the solution at the mixing head while agitating the solution with the mixer so as to break up the introduced smoke into bubbles. Operation of the method to agitate the solution and break up the bubbles may create reduced pressure at the point of smoke introduction, reduced compared with pressure at the smoke source. Hence, the method preferably comprises agitating the solution such that smoke is drawn into the mixing head. The mixer is suitably capable of operating so as to create reduced pressure in the solution to draw smoke into the solution in the smoking vessel. The method can be used unpressurised, e.g. with no need to pump smoke into the solution. Suitable mixing heads comprise a mixing blade, and the method can then comprise introducing smoke in close proximity to the blade. Control of blade rotation can be used to control bubble size and incorporation of smoke into the solution Preferred methods comprise introducing the smoke via a conduit, e.g. pipe, with an exit below the solution surface and close to a blade of the mixing head. The exit is immersed in the solution during operation. The mixing head may comprise a rotor blade (which moves) and a stator. Referring to examples below, in a preferred arrangement the pipe exit is attached to stator, hence being able to reliably deliver smoke to the desired location with respect to the moving blade(s).

Introducing the smoke close to the blade(s) increases break-up of the smoke, and methods suitably do so no more than 10cm from the blade(s), preferably no more than 3cm, more preferably no more than 2cm from the blade(s), most preferably no more than 1 cm from the blade(s). Scale of apparatus can be relevant to the dimensions concerned. In small scale apparatus described below, smoke was bubbled into the solution approximately 6mm from the moving mixer blades.

In general, a wide range of mixers are suitable for the methods of the invention, meaning especially suitable for introducing smoke into the liquid to be smoked broken up into the form of multiple, small bubbles, with high surface area so that volatiles and smoke components are dissolved into the liquid more rapidly than with known passive smoking methods. The mixers may also be referred to as blenders that combine the smoke with the liquid; they generally comprise one or more, usually a plurality of, blades or vanes or impellers that move, commonly these rotate and are motor driven.

Preferred mixers have a mixing head including a rotor and a stator, and preferred methods and apparatus use a mixer such that the smoke can be introduced at the head and close to the rotor. Further preferred mixers comprise a conduit for smoke so that smoke can be pumped into and/or sucked into (e.g. operation of the rotor may create a partially negative pressure compared with pressure in the smoke generator) the liquid and delivered at the mixing head. In use of such mixers, smoke can be introduced into a region of turbulent flow at or around the mixing head, resulting in a greater degree of breaking the smoke into fine bubbles, increasing the rate of dissolution of smoke components. In an embodiment of the invention described in examples below, a pipe is provided (as part of the mixer, though this is not essential) with an outlet at the mixing head, close to (in the mixer used approximately 6mm from the moving mixer blade(s), though again this precise distance is not essential) the mixer blade(s) so that smoke is delivered into a region of turbulence during mixing, so that the smoke is rapidly and violently broken up in microbubbles; these microbubbles have small diameters, much smaller than the introduced smoke exiting the pipe, having diameters of 5mm or less, suitably 2mm or less, preferably 1 mm or less, 0.5mm or less and even smaller.

A suitable mixer is made by Silverson®, named a Mixer Homogenizer, adapted to take a gaseous (i.e. smoke) input. The mixer workhead generates high shear rates in a three stage mixing/homogenizing process: a high speed rotor draws materials into the workhead, where the smoke and liquid are intensely mixed; centrifugal force then drives the materials to the periphery of the workhead and subjects them to mechanical shear in a gap between the rotor and stator; this is followed by hydraulic shear, as the product is forced through a stator screen at high velocity and circulated back into the mix. Fresh material is continually drawn into the workhead supplemented by smoke input.

Another particularly suitable mixer, used in examples below, is made by YTRON Process Technology GmbH & Co. KG, Germany, named the YTRON Y ByPass mixer, a range that comes in differing sizes and powers. These have a side pipe designed originally for powder or high viscosity products to be introduced directly into the liquid at the mixing head; in our adapted use of the mixers the pipe delivers the smoke to the head. The Y-tron allows for variable shear settings, e.g. by adjustment of impeller speed. In water smoking (not part of the present invention but included for comparison) shear was adjusted by setting impeller speed to approx. 60 - 70 Hz. In e-liquid smoking as described herein shear was typically reduced, with the speed set lower, typically to 30 - 60 Hz, and more specifically about 50 Hz in examples. Mixer operation, whether low shear or high shear can create turbulence in the solution, and preferred methods comprise agitating the solution so as to create a region of turbulent flow in the solution and introducing the smoke into that region. Known smoking methods are inefficient in that smoking takes a long time or uses only a small proportion of the smoke which, to avoid being wasted, has to be recirculated in complex, closed pipework in apparatus operated using special control equipment. It is an advantage that the methods herein can be carried out without the need for closed equipment. Hence, preferred methods comprise venting the smoking vessel to the atmosphere. Emissions from typical fuels are generally not unduly toxic and venting directly to the outside is usually acceptable. The bubbling through the solution provides a significant extent of scrubbing. The methods may, however, also comprise scrubbing off-gas prior to venting, for example to remove identified combustion products not absorbed into the solution.

It is further preferred that the methods comprise no recirculation of off-gas back through the solution. There is no need to do so when smoke incorporation into the solution is efficient, and the complication and expense of such recirculation piping etc. is avoided.

The degree of solution agitation may be adjusted, according to solution type, smoke flow, smoke content and other parameters. It is a feature of the invention that such adjustment can be carried out to provide an efficient process utilising a high proportion of the smoke generated in a single pass.

Preferred methods of the invention comprise monitoring the method and adjusting the agitation to reduce to a minimum the smoke bubbles that escape from the solution being smoked. Hence, smoke components are captured without any need for smoke recirculation (as noted above) and with no or minimal smoke waste. In examples of achieving such efficiencies, the methods may entail increasing the agitation until no or substantially no smoke bubbles escape. A further step may be, once this point is reached, to make a small reduction in agitation until smoke bubbles escaping begins to be noticeable. Thus, a user can increase the agitation (for example by increasing mixer speed or reducing smoke flow) until there is more or less no smoke passing through the solution. This may be seen as absence of frothing at the solution surface or absence of significant quantities of off-gas exiting e.g. via a venting chimney. This may be seen as only a tiny proportion of small bubbles reaching the solution surface. A small decrease in agitation, hence leading to a small but minimal level of bubbling at the surface, may then establish a desired throughput smoke level for long term and efficient operation of the method. In methods below calibration over several trial runs led to the combination of flow and agitation adopted in the examples.

In general, it is hence desired to capture a significant proportion of the smoke in a single pass. Suitably, the methods comprise agitating the solution so that 50% or less of the smoke bubbled into the solution escapes from the solution, preferably so that 30% or less of the smoke bubbled into the solution escapes from the solution, more preferably so that 20% or less of the smoke bubbled into the solution escapes from the solution. This proportion is even more preferably 10% or less and in specific examples carried out below we have estimated that smoke capture is at or exceeds 95%, i.e. 5% or less escapes the first pass bubbling.

The invention also provides smoked e-liquids made by a method of the invention. These are useful in the e-cigarette industry.

Further provided by the invention is apparatus for smoking e-liquids according to all methods of the invention. Apparatus of embodiments of the invention, for treating an e-liquid solution, comprises:

a smoke chamber having an air input and a smoke output and in which fuel can be combusted to generate smoke;

a smoking vessel (e.g. pan) capable of holding the solution to be treated;

a mixer for mixing contents of the smoking vessel;

a conduit from the output of the smoke chamber to the smoking vessel with an exit for introducing the smoke into the solution, below the surface of the solution; wherein the apparatus, e.g. via mixer features, is adapted to break up the introduced smoke into bubbles, especially whereby the mixer is adapted to agitate the solution so as to break up the introduced smoke into bubbles. In preferred apparatus, the vessel is pre-charged with the e-liquid to be treated, i.e. is supplied already holding / containing the e-liquid to be treated.

The water vessel can have a range of capacities and is not the object of the invention. Suitable pans are well known in the food industry and enable the smoking and mixing process to be carried out. Preferred vessels are partially or substantially wholly circular in cross section - during mixing in embodiments as described herein this shape enabled the mixed solution to rotate around a mixing head, giving extended residence times to bubbles and leading to improved dissolution of smoke volatiles.

Smoke can flow naturally into the mixer, and certain mixers as described elsewhere herein may exert a negative pressure to pull smoke into the solution. Preferably, smoke is pumped into, or additionally pumped into, the smoking vessel. This can be achieved in apparatus that comprise a pump, e.g. compressor, to force air into the chamber and force smoke into the smoking pan. Throughput rates can vary, and may depend upon apparatus scale. 10 L/minute and above, e.g. 50L/minute and above are suitable rates. In small scale apparatus we used about 125-130L/minute, though different flow rates will apply to different sizes and setups, especially higher flow rates for larger scale apparatus. These flow rates can be monitored and adjusted as part of adjusting the overall process to ensure a low level of smoke escaping from the smoked solution.

The apparatus preferably comprises a chimney to vent the smoking vessel directly to the atmosphere, and may comprise a unit to scrub off-gas prior to venting. As described in relation to the methods herein, the apparatus preferably has no conduit permitting recirculation of off-gas back through the solution - the efficiency of the process means none is needed. Monitoring and control equipment is suitably provided within the apparatus, for monitoring the method and adjusting the agitation to reduce to a minimum the smoke bubbles that escape from the solution being smoked. Operating the monitor and controls enables the user easily to control the process and achieve high efficiency smoking - e.g. increasing the agitation until no or substantially no smoke bubbles escape and then reducing the agitation until smoke bubbles escaping begins to be noticeable.

As per preferred methods, preferred apparatus use or comprise a filter for filtering the smoke before it is introduced into the solution. Filter features are suitable as described in relation to the methods of the invention.

Methods of the invention may operate so as to increase incorporation of smoke and/or smoke components into solution, and the methods suitably comprise cooling the solution and/or the smoke prior to and/or during smoking. Preferably, the solution is cooled during the smoking process. This may be achieved e.g. by cooling the chamber or vessel holding the solution. In specific examples, the chamber or vessel is cooled using a cooling jacket or blanket. Methods of the invention can result in rapid incorporation of (relatively hot) smoke into solution, resulting in significant temperature rises not seen in known smoking processes. In trials in the absence of such cooling we unexpectedly encountered solution temperatures in excess of 40°C. During smoking it is preferred that the solution is subjected to cooling so as to be maintained at or below 30°C, preferably below 20°C, more preferably below 15°C or below 10°C. An advantage of this cooling is that higher levels of gaseous smoke components can be dissolved. The methods of the present invention may thus achieve a fast and efficient transfer of smoke into solutions through a combination of increased smoke incorporation with cooling to increase the solubility of smoke components. Apparatus of the invention may comprise a cooler to cool the solution during smoking, optionally with a controller to maintain the solution at or below a desired temperature as per the above. During operation, the apparatus preferably is loaded with, hence comprises, fuel mixed with filter material.

The apparatus preferably comprises a mixer adapted to break up smoke into tiny bubbles and homogenise them into the liquid rapidly and efficiently. Optional and preferred mixer features are as described above in relation to the methods of the invention.

In general, the fuel for the source of the smoke is not limited, provided that the smoke is regarded as useable for e-liquids, which are for human consumption. Smoke is typically generated from a combustion material or fuel provided in a form that is relatively dry and can be combusted to yield smoke to generate smoke flavour. Tobaccos is a preferred fuel for e-liquids, preferably filtered. Common materials used in the industry for generating smoke are: wood chips, wood dust, wood shavings, wood briquettes, logs, charcoal and charcoal briquettes. Oak, hickory, cherry, apple and beech wood are suitable. Other suitable woods and other smoke sources include alder, barley, malted barley, black walnut, red oak, honey oak, walnut, cedar, chestnut, corn cobb, maple, mesquite, mulberry, orange, pear, pecan, plum, and sandalwood and also mixtures thereof.

In examples described below, e-liquids have been smoked with tobacco smoke, wood smoke and smoke from a mixture of tobacco and various woods. Smoking in those cases and at the scales used to dates was typically over approximately 1 -4 hours, e.g. about 4 hours to smoke 6 litres of propylene glycol using 1 kg of cherry wood, about 4 hours to smoke 6 litres of propylene glycol using 1 kg of a 1 :1 mix of tobacco and cherry wood and about 2 hours to smoke 2 litres of propylene glycol with 500g of oak as fuel. Other fuel mixtures are set out specifically in the examples. Use of a filter present in the fuel is optional though was used in all cases for these examples.

E-liquids of the invention may also be flavoured with menthol, peppermint, cherry, grape, chocolate, coffee, vanilla, cola and/or peach. They may additionally, contain in final form, optionally in the base, nicotine in varying concentrations. The tobacco may be of varying types / flavours including: traditional, Virginia, Turkish. In addition to the above, fruit flavours such as apple, strawberry, blueberry and watermelon are also options. Other suitable flavours include cinnamon, vanilla pods, mint leaves, cherry stones and botanicals in general. E-liquids prepared by methods comprising smoking tobacco or tobacco / other fuel mixes may as a result contain some nicotine. Generally, for consistent levels, nicotine levels are measured after smoking and adjusted according to the level desired in the end product. Specific embodiments of the invention combine optional and/or preferred features as described herein, and hence a preferred method comprises:

(i) providing a source of smoke that has optionally been filtered to reduce its PAH content,

(ii) providing a smoking vessel (e.g. pan) containing the e-liquid solution, and (iii) introducing bubbles of smoke into the solution at a mixing head of a mixer and no more than 3cm from a blade of the mixer, while agitating the solution with the mixer blade so as to break up the introduced smoke into a plurality of bubbles of average diameter 2mm or less,

(iv)venting the smoking vessel to the atmosphere, and

(v) cooling the solution so as to maintain it at a temperature of 30°C or below.

The invention thus provides a method of mixing filtered, or unfiltered, smoke into e- liquids, using a mixer, specifically a YTRON-Y ByPass model, for use in the e- cigarette industry.

Various concentrations of smoked e-liquid can be made for stronger or milder flavour, rated according to the level of filtration of the smoke and/or the duration of smoking (corresponding to flavour intensity). The higher the filtration rating the fewer carcinogens there are in the smoke used.

The smoking technique can be used for e-liquids and this term embraces bases intended for further processing into end product e-liquids. The method can thus be used to mix filtered or unfiltered smoke into solutions of humectants such as propylene glycol or glycerol etc based compositions, optionally also water-containing, for use as an e-cigarette liquid. Smoking of these with tobacco smoke can create the density and flavour of smoke that cigarette smokers feel when inhaling and therefore be more satisfying for the e-cigarette user. Filtering the smoke additionally means that this can be achieved with reduced carcinogen content, especially reduced PAH content.

The time needed for smoking e-liquids according to the invention is low and hence efficient compared with known times in existing water smoking methods.

An advantage of filtered embodiments of the invention is the retention of desirable flavours, while removing some or most or substantially all of certain larger, undesired PAHs - found especially in wood smoke. The treating optionally comprises filtering the smoke selectively to remove the PAHs that contain 4 or more benzene rings compared with removal of naphthalene and/or phenanthrene. Generally, the treating comprises filtering the smoke selectively to remove the PAHs that contain 4 or more benzene rings compared with removal of smoke-flavoured components from the smoke. In preferred embodiments of the invention, exemplified in examples below, the treating comprises filtering the smoke selectively to remove the PAHs that contain 4 or more benzene rings without significantly changing the volatile profile of the smoke compared with unfiltered smoke.

An additional advantage of filtered embodiments of the invention is the reduction in or removal of ammonia as a by-product of smoking tobacco into the e-liquid; the resulting tobacco-smoked e-liquids have reduced pH levels, being less alkaline than hitherto.

Further advantages of the invention, illustrated in embodiments described herein are enhancement of flavour in the products obtained. The examples showed flavour improvements, including one or more of tar removal, reduced acidity, reduced acridity, reduced PAH and/or reduced ammonia - dependent upon the combustion material. When using filtered smoke, it is found that the smoking generated significantly reduced carbonic acid levels (due to reduced amounts of dissolved CO₂) compared with smoking using unfiltered smoke (i.e. prior art smoke). Testing of products comparable with known smoked products (but prepared with unfiltered smoke) has indicated higher pH due to reduced acidity caused by reduced levels of acid-forming combustion products (such as CO₂). In one example, PST50 filtration reduced carbonic acid to 15% of the levels in a control smoked with unfiltered smoke, with the product having pH increased approximately 0.5 to 1 .0 pH units. Also, reduced acridity, meaning reduced bitter or pungent taste, is particularly significant for consumers. Wood smoked e-liquids had higher pH than known smoked water (used as initial reference point), i.e. the invention produces less acidic products for such fuels. Preferred products smoked with wood have pH 4 or greater, 4.5 or greater, 5 or greater or 5.5 or greater. More generally, however, the pH of the smoked e-liquid varies according to presence or absence of filter and the choice of fuel - details are in the examples. Tobacco smoke was found to give more alkaline e-liquids, with pH generally in the range pH 6 - 10, more specifically 6.5 - 9.0. Wood smoke produced lower pH e-liquids, generally in the range of pH 3 - 6, more specifically pH 4 - 5. Mixtures gave intermediate pHs: a specific tobacco/oak mix gave pH 5.8 - 6.0 and a tobacco/cherry mix gave pH 6.5 - 8.5. Using a filter for wood smoke tended to increase the pH as the filter removes acidity from the smoke. Using a filter for tobacco smoke tended to reduce overall pH due to ammonia reduction. Hence, by adjusting the choice of fuels and their ratio and also whether to use the filter (and if so at what level of filter) the pH can be adjusted according to customer preference.

Currently e-cigarette liquids are heated and create a vapour that is inhaled. This vapour lacks the density of cigarette smoke. The use of smoked tobacco e-liquids as per the invention introduces the volatiles of cigarette smoke; using filtration according to the invention reduces or removes harmfuls such as PAHs/ammonia while retaining the desired smokey flavours.

The invention is now described in specific examples with reference to the accompanying drawings in which: Fig. 1 shows a schematic diagram of a laboratory-scale smoker of the invention;

Fig. 2 shows a schematic diagram of a industrial-scale smoker of the invention;

Fig. 3 shows a star diagram of the results of testing mouthfeel and after effects of chicken brined in water smoked according to the invention: A smoked with no filtration, B-D increased levels of filtration from B to D;

Fig. 4 shows a star diagram of the results of testing taste of chicken brined in water smoked according to the invention: A smoked with no filtration, B-D increased levels of filtration from B to D;

Fig. 5 shows a star diagram of the results of testing flavour of chicken brined in water smoked according to the invention: A smoked with no filtration, B-D increased levels of filtration from B to D;

Fig. 6 shows a plot of smoking time (hours) vs pH of smoked water, comparing the smoking method of the invention with the smoking method described in US 2012/0207898; and

Fig. 7 shows a plot of smoking time (hours) vs luminosity of smoked water, comparing the smoking method of the invention with the smoking method described in US 2012/0207898.

Examples

Example 1 - Laboratory Scale Water Smoker

We developed a water smoker 10 for preparation of smoked water, calibrated it, made smoked water, brined chicken in the smoked water and tested the chicken.

A compressor 12 was linked by pipe 14 to airtight smoke chamber (approx. 100 litres) 16, containing combustible material 20 (wood dust optionally with added filter material). The chamber smoke output was in turn linked to the stator portion of mixing head 28 of a YTRON® Y-ByPass mixer 24 via silicone rubber linking tube 22 and bypass pipe 26. The mixer is approximately 0.6m tall with a power of 4.5KW. The mixing head 28 is submerged during operation in water in a circular cross- section water pan (approx. 15 litres) 30. Calibration Run - we smoked water using the apparatus for periods varying from 1 hour to 24 hours and compared the intensity of the product with conventionally obtained smoked water made in-house by the inventor using static water trays. Air was flowed into the smoke chamber 16 at approximately 127 litres per minute. Oak dust was placed in the bottom of the chamber (replenished as required) and electrical heat source 18 was switched on to ignite the dust, producing smoke. The air flow directed smoke to the mixing head via the linking tube and the bypass pipe. The mixer was turned on and also exerted a low level of suction, thus drawing smoke down the bypass pipe and into the water in the pan. The bypass pipe exit was of diameter approx. 25mm and was located approximately 6mm above the spinning impellers (set to approx. 60 Hz) of the mixer inside the mixing head, delivering the chamber output smoke right into the centre of the mixing; as the impellers span the smoke was intimately homogenised into tiny bubbles at the centre of the mixing head, with frothing seen at and around the head and at the water surface. Tiny bubbles were also seen dispersed throughout the water, swirling in the mixed water, having long residence times before rising to the surface. The few bubbles of smoke passing through the solution escaped into the atmosphere directly.

The smoked water made by smoking for 6 hours according to the invention was found comparable to water smoked in trays in a smoker for 4 days.

Brine for brining chicken was then prepared as follows. Air was flowed into the smoke chamber 16 as before. Initially, 2kg of oak dust was placed in the bottom of the chamber and electrical heat source 18 was switched on to ignite the dust, producing smoke. This amount of dust was by then known to burn for approximately 4 hours so after a little less than 4 hours a further 1 Kg of dust was added to give a total burn time of approximately 6-7 hours.

The smoking and mixing was continued for approximately 6 hours, then the compressor and mixer switched off and the remaining dust left to extinguish by cutting off the air supply. Run A - The smoked water was removed and then used as brine for chicken pieces, which were left to soak in the smoked water for 24 hours. This run was referred to as unfiltered. Runs B-D - The process was then repeated, with alternative fuel sources (retaining the same amount of oak but supplemented with clinoptilolite filter as described in WO 2015/007742), these runs being referred to as with increasing levels of filtration:

B oak dust plus clinoptilolite at weight ratio 4:1 ("PST 25")

C oak dust plus clinoptilolite at weight ratio 2:1 ("PST 50")

D oak dust plus clinoptilolite at weight ratio 1 :1 ("PST 100")

The chicken pieces from the brines of runs A-D were then tested as now described, with reference to fig.s 3, 4 and 5. Fig. 3 shows a star diagram of the results of a sensory panel tasting of the chicken for mouthfeel and after effects. The more filtration that was introduced the more balanced the flavour became, with less 'ash tray' qualities.

Fig. 4 shows a star diagram of the results of a sensory panel tasting of the chicken for overall taste. These results recorded a more desirable flavour profile for runs B-D, D scoring highest, complementing the chicken by improving the umami, salt and sweet flavour character.

Fig. 5 shows a star diagram of the results of a sensory panel tasting of the chicken for flavour. Interestingly, the panel reported an improved balance of flavours, which allowed the chicken flavour to come through whilst reducing the flavours associated with acridity, smokiness and smoked fish.

Example 2 - Industrial Scale Water Smoker

An industrial scale water smoker 40 was designed for larger scale water smoking.

Combustible materials (e.g. wood, botanicals) are fed from container 42 into industrial smoke generator 44. The smoke passes through linking pipe 46 to bypass pipe 48, which delivers the smoke directly into the mixing head 58 of large scale homogeniser 50. We designed this smoker to work with a known YTRON® Y- ByPass mixer of power 1 1 .5KW. The mixing head 58 is suspended in a water vessel 54 containing up to 5,000 litres of liquid. The smoked liquid is collected from the vessel 54 by tap 56. Bubbles of smoke passing through the solution are vented directly to the atmosphere via a short chimney (not shown). The chimney allows for inclusion off-gas scrubbing units if desired, e.g. according to local emissions regulations.

Example 3 - pH Testing Of Smoked Water

We smoked water as per the prior art method referred to the calibration run of Example 1 and compared its pH with water smoked according to the invention using no filtration and then filtration levels PST25 and PST50. The filtered, smoked water of the invention had higher pH, i.e. was less acidic, than known smoked water: Smoked Water (prior art) pH

Standard tray-smoked water 3.9

Smoked Water (invention)

No filtration 3.9

PST25 4.5

PST50 5.7

Example 4 - Smoking of e-Liquids

Based on the above examples for smoking water and initial testing of smoking mixtures of propylene glycol (PG) and glycerol (VG), we devised a protocol as follows: repeat the runs B-D of example 1 substituting 60% PG / 40% VG and smoking tobacco in the chamber for 2 hours. Initially we smoked 6 litres of propylene glycol using 1 kg of cherry wood for 4 hours, 6 litres of propylene glycol using 1 kg of a 1 :1 mix of tobacco and cherry wood, again for 4 hours, and then 2 litres of propylene glycol with 500g of oak as fuel for 2 hours. Testing of these batches confirmed the parameters for the subsequent smoking in examples below, following the example 1 method though with slightly reduced Y-tron speed (set to 50 Hz) to reduce smoke escape to virtually zero. Furthermore, it was observed that when 4 litres of PG was smoked with 1 .3kg tobacco, a certain quantity of ammonia was also filtered out from the samples containing filter material. This was confirmed by sensory data - a PST100 sample demonstrated a cleaner tobacco aroma with less detectable ammonia, whereas non- filtered smoked sample had a strong ammonia aroma. Also, the pH of the sample treated with filtered smoke was 7.8, compared with 8.8 in the comparative unfiltered smoked sample. Example 5 - Smoking of e-Liquids

Following the method of previous examples, we carried out 15 further e-liquid smoking runs using 100% MPG (monopropylene glycol). All samples were smoked using equipment with smoke bubbling adjusted for minimum escape of smoke from the solution after a single bubbling. In calibration runs, agitation was increased until virtually no smoke bubbles emerged from the solution and then agitation was turned down by decreasing mixer speed slightly until small numbers of the tiniest bubbles were noticeably rising all the way to the solution surface, with a mild smoke smell emerging from the smoker chimney vent. Samples used in the runs below were:

1 . Pure Tobacco 4 hours Control, PST50, PST100

2. Tobacco-Oak Wood 4 hours Control, PST50, PST100

3. Tobacco-Cherry Wood 4 hours Control, PST50, PST100

4. Cherry Wood 4 hours Control, PST50, PST100

5. Oak Wood 2 hours Control, PST50, PST100

(PST50 = 2 fuel : 1 filter, w/w; PST100 = 1 fuel : 1 filter)

Control samples were smoked with un-filtered smoke. PST50 was a medium level of filtration and PST100 was the highest level of filtration used in the examples.

During smoking, samples were taken every hour for sensory and pH testing. Table 1 below presents the sensory characteristics of relevant samples at the end of the smoking process, with preliminary conclusions: Table 1

PH Visual Aroma Smoking Comments Aspect test

Sample Burning mix/smoking length

Pure Tobacco 4 hours

Control 8.9 Dark- Very strong Mild tobacco Not

BATCONTROL1 yellow, ammonia flavour. significantly brownish aroma. Some different cloudy ashtray notes. from PST liquid. smokes.

PST50 8.9 Light- Strong Mild tobacco Not

BATPST50T1 yellow, ammonia flavour significantly straw- aroma. different coloured from clear control. liquid.

PST100 9.0 Light- Strong Mild tobacco Not

BATPST100T1 yellow, ammonia flavour. significantly straw- notes. Pleasant. different coloured from clear control. liquid.

Sample Burning mix/smoking length

Tobacco-Oak Wood 4 hours

Control 6.0 Amber- Smoky, More like a Needs

BATCONTROLTO1 coloured pleasant cigarette, more

clear aroma, with some strength liquid. some ashtray ashtray and depth.

notes. notes.

PST50 5.9 Light- Tobacco Quite woody Increase

BATPST50TO1 yellow, smoke aroma. smoke, the amount straw- Some ashtray obvious of tobacco. coloured notes. vanilla notes.

clear

liquid.

PST100 5.9 Very pale, Mild tobacco Quite woody Increase

BATPST100TO1 almost smoke aroma. smoke, the amount colourless Some ashtray obvious of tobacco. clear notes. vanilla notes.

liquid.

Sample Burning mix/smo king length

Tobacco-Cherry Wood 4 hours

Control 8.4 Amber- Mild smoke, Very mild

BATCONTROLTC1 coloured quite strong tobacco

clear ammonia flavour.

liquid. character,

some petrol

notes.

PST50 6.5 Light- Mild smoke. Mild BATPST50TC1 yellow, Marzipan and tobacco,

straw- petrol notes. fruity flavour.

coloured Sweet finish.

clear

liquid.

PST100 7.2 Light- Mild smoke. Mild More

BATPST100TC1 yellow, Marzipan, tobacco, pleasant straw- some petrol fruity flavour. than coloured notes. Sweet finish. control. clear

liquid.

Sample Burning mix/smoking length

Pure Cherry Wood 4 hours

Control 4.5 Dark- Mild, smoky

BATCONTROLC1 yellow aroma with

clear notes of

liquid. marzipan.

PST50 4.4 Dark- Mild, sweet Sweet, fruity

BATPST50C1 yellow aroma. Some flavour.

clear resiny notes.

liquid.

PST100 4.9 Light- Mild smoky, Sweet, fruity

BATPST100C1 yellow fruity aroma. flavour.

(straw- Some woody

coloured) notes.

clear liquid

Sample Burning mix/smoking length

Pure Oak Wood 2 hours

Control 3.9 Clear, Mild smoky Pleasant

161 1 10 amber aroma. smoke.

coloured Woody,

liquid. cigar-like

character.

PST50 4.3 Clear, Mild smoky Pleasant

161 1 10PST50 light-amber aroma. mild smoke.

coloured Woody,

liquid cigar-like

character.

Vanilla

notes.

PST100 4.8 Clear, Mild smoky Pleasant

161 1 14PST100 light-yellow aroma. smoke.

liquid. Woody,

cigar-like

character.

Vanilla

notes. Preliminary conclusions from the sensory evaluation indicated that the product with the most typical tobacco flavour was the tobacco smoked MPG (Control, PST50, and PST100) even though the content of ammonia in smoke was quite high. Mixing tobacco with oak neutralised the ammonia and decreased the pH of the smoke. However, when using filtration, the woody character starts to prevail, particularly vanilla notes. This effect may be adjusted by changing the tobacco/wood ratio. Intensity and depth can be changed with varied smoking duration. Preliminary data (from other runs, not documented) indicated as specific examples that hickory smoke can add intensity and beech smoke can add depth. Mixing tobacco with cherry wood imparted a sweet, fruity flavour making the smoke slightly milder. It also neutralised the ammonia without adding a significant woody character.

Example 6 - Comparative Study

We compared the efficiency of the smoking method of the invention with smoking methods known in the prior art. Specifically, the prior art smoking method involved passively introducing small bubbles of smoke into the water, as in US 2012/0207898.

As in Example 1 , a compressor 12 was linked by pipe 14 to airtight smoke chamber (approx. 100 litres) 16, containing combustible material 20 (wood dust). The chamber smoke output was in turn linked to the stator portion of mixing head 28 of a YTRON® Y-ByPass mixer 24 via silicone rubber linking tube 22 and bypass pipe 26. The mixer is approximately 0.6m tall with a power of 4.5KW. The mixing head 28 is submerged during operation in water in a circular cross-section water pan (approx. 15 litres) 30.

Air flowed into the smoke chamber 16 at approximately 127 litres per minute. Oak dust was placed in the bottom of the chamber (replenished as required) and electrical heat source 18 was switched on to ignite the dust, producing smoke. The air flow directed smoke to the mixing head via the linking tube and the bypass pipe. The mixer was turned on and also exerted a low but notable level of suction, thus drawing smoke down the bypass pipe and into the water in the pan. The bypass pipe exit was of diameter approx. 25mm and was located approximately 6mm above the spinning impellers (set to approx. 60 Hz) of the mixer inside the mixing head, delivering the chamber output smoke right into the centre of the mixing; as the impellers span the smoke was intimately homogenised into tiny bubbles at the centre of the mixing head, with frothing seen at and around the head and to a lesser extent at the water surface. Tiny bubbles were also seen dispersed throughout the water, swirling in the mixed water, having long residence times before rising to the surface. The few bubbles of smoke passing through the solution were vented into the atmosphere directly.

In the comparative run, water was smoked in the same way (fuel, amount of fuel, air flow, water pan, smoke chamber etc.) but instead with the chamber smoke output linked to a perforated nozzle submerged in the water pan. The perforated nozzle was configured to closely simulate the effect of the mesh used in US 2012/0207898, thereby breaking up the smoke into fine bubbles as the smoke entered the water. It was felt not necessary to replicate the closed nature of the system of US 2012/0207898, as this feature was determined to have no or insignificant on the rate at which smoke is introduced into the water; rather, the closed system acts to reduce fuel consumption by re-circulating generated smoke multiple times. It is arguable, even, that the replication carried out in this comparative study is more effective than the setup in US 2012/0207898 at introducing smoke into water quickly; this is because newly generated smoke, containing a higher saturation of smoke components than recirculated smoke, is continually being introduced to the water.

During smoking, all parameters were controlled and matched between the respective methods. Continuous pH measurement was performed using an Edge pH meter (Hanna Instruments). Colour measurements were taken under standard illumination and analysed using the Pantone application. Sensory analysis was also performed.

Statistical analysis was carried out using ANOVA in combination with a post-hoc Tukey test. The results are shown in Fig.s 6 and 7. Results are presented as mean +/- standard deviation and are considered significant when p < 0.05.

As illustrated in Fig. 6, a faster decrease in the pH of smoked water is observed when using the smoking method of the invention (dashed line), opposed to the passive bubbling method of the prior art (solid line). Commercially, smoked water is commonly sold at a pH of around 4.0. Using the smoking method of the invention, this pH was reached after around 2 hours of smoking, whereas the prior art method as per the reproduction herein required 6 hours of smoking to achieve a similar decrease in the pH of the water. Furthermore, it was observed that pH starts to plateau at around pH 4 using the reproduced prior art smoking method, whereas using the smoking method of the invention the pH started to plateau at around pH 3. This suggests that a more concentrated smoked water is achievable using the smoking method of the invention.

Luminosity of the smoked water is outlined in Fig. 7. It is observed that the luminosity of the water smoked using the smoking method of the invention (dashed line) decreases more quickly than when the water is smoked using the reproduced prior art smoking method (solid line). As a decrease in luminosity represents a higher degree of smoke integration into the water, these data confirm that the smoking method of the invention was a more powerful and more time-efficient method that that of the prior art. Again, it is shown that a similar luminosity (~67) is achieved after 2 hours using the smoking method of the invention, versus 6 hours using the reproduced smoking method of the prior art. Additionally, it is observed that a far lower luminosity (-46) is achievable when water is smoked for 6 hours using the smoking method of the invention.

Furthermore, in respect of both pH and colour (luminosity) measurements, the results obtained for each hourly time point demonstrate a higher degree of reliability between individual experiments (n=3) for the smoking method of the invention. This can be seen in Fig.s 6 and 7, respectively, which both clearly show reduced standard deviation from the mean for the smoking method of the invention (dashed line) versus the prior art smoking method (solid line), indicating the invention provides a consistent and reproducible process.

The pH and colour measurements described above correlate strongly with sensory data obtained and illustrated in Tables 2 and 3:- Sample Colour Aroma Taste

1 hr Pale yellow, Mild smoke. Mild smoky taste. Slightly straw-coloured oily.

2 hrs Light-yellow Mild smoke. Mildly acidic, smoky.

3 hrs Light-yellow Smoky. Acidic, smoky, slightly

bitter.

4 hrs Rich yellow Very smoky. Very acidic, smoky, bitter.

5 hrs Light-amber Very smoky, slightly Very acidic, very smoky, woody. bitter.

6 hrs Amber Very smoky, woody, Very acidic, very smoky, rich. bitter, oily.

Sensory analysis of samples smoked with the smoking method of the

Table 3 - Sensory analysis of samples smoked with the reproduced smoking method of the prior art.

The smoking method of the invention can thus be used to produce smoked water quickly and easily when compared with other known smoking methods in the prior art, in particular that described in US 2012/0207898. Accordingly, the invention provides methods and apparatus for smoking e-liquids, especially using filtered smoke.

Parts List for Smokers

10 water smoker

12 compressor

14 connection pipe

16 smoking chamber

18 heat source

20 combustible material

22 connection tube

24 homogeniser

26 bypass pipe

28 mixing head

30 water pan

40 industrial water smoker

42 combustible material container

44 industrial smoke generator

46 connection pipe

48 bypass pipe

50 homogeniser

58 mixing head

54 liquid vessel

56 tap

Claims

1 . A method of treating an e-liquid solution to make a smoked e-liquid, comprising:

(ii) providing a smoking vessel (e.g. pan) containing the solution, and

(iii) introducing bubbles of smoke into the solution at a mixing head of a mixer and no more than 3cm from a blade of the mixer, while agitating the solution with the mixer blade so as to break up the introduced smoke into a plurality of bubbles of average diameter 2mm or less,

(iv) venting the smoking vessel to the atmosphere, and

2. A method of treating an e-liquid solution to make a smoked e-liquid, comprising:

(i) providing a source of smoke,

(ii) providing a smoking vessel (e.g. pan) containing the solution, and

(iii) introducing bubbles of smoke into the solution while agitating the solution so as to break up the introduced smoke into a plurality of smaller bubbles, wherein a negative pressure compared with pressure in the smoke source causes smoke to be sucked into the solution.

3. A method according to any previous claim comprising filtering the smoke to reduce its PAH content.

4. A method according to any previous claim comprising treating the smoke to selectively remove therefrom one or more PAHs that contain 4 or more benzene rings.

5. A method according to any previous claim, comprising selectively removing benzo(a)pyrene, benz(a)anthracene and/or dibenz(a,h)anthracene from the smoke.

6. A method according to any previous claim, comprising generating smoke in the presence of filter material and/or passing smoke through a filter.

7. A method according to any of claims 2 to 6 comprising breaking the smoke into bubbles of average diameter 5mm or less.

8. A method according to claim 7, comprising breaking the smoke into bubbles of average diameter 2mm or less.

9. A method according to any of claims 2 to 8, comprising apparatus having a mixer with a mixing head immersed in the solution, and the method comprising introducing the smoke into the solution at the mixing head while agitating the solution with the mixer so as to break up the introduced smoke into bubbles.

10. A method according to claim 9 wherein the mixing head comprises a mixing blade, and the method comprises introducing smoke in close proximity to the blade.

1 1 . A method according to claim 9 or 10 comprising introducing the smoke via a pipe with an exit below the solution surface and close to a blade of the mixing head.

12. A method according to claim 1 1 wherein the mixing head comprises a rotor blade and a stator, and wherein the pipe exit is attached to the stator.

13. A method according to claim 1 1 or 12, comprising introducing the smoke no more than 10cm from the blade.

14. A method according to claim 13, comprising introducing the smoke no more than 3cm from the blade.

15. A method according to any of claims 2 to 14 comprising agitating the solution so as to create a region of turbulent flow in the solution and introducing the smoke into that region.

16. A method according to any of claims 2 to 15, comprising venting the smoking vessel to the atmosphere.

17. A method according to claim 16, comprising scrubbing off-gas prior to venting.

18. A method according to any previous claim, wherein there is no recirculation of off-gas back through the solution.

19. A method according to any previous claim, comprising monitoring the method and adjusting the agitation to reduce to a minimum the smoke bubbles that escape from the solution being smoked.

20. A method according to claim 19, comprising increasing the agitation until no or substantially no smoke bubbles escape and then reducing the agitation until smoke bubbles escaping begins to be noticeable.

21 . A method according to any previous claim, comprising agitating the solution so that 50% or less of the smoke bubbled into the solution escapes from the solution.

22. A method according to any previous claim, comprising agitating the solution so that 30% or less of the smoke bubbled into the solution escapes from the solution.

23. A method according to any previous claim, comprising agitating the solution so that 20% or less of the smoke bubbled into the solution escapes from the solution.

24. A method according to any previous claim, wherein the solution comprises salt, sugar, spices and/or other flavours.

25. A method according to any previous claim, comprising cooling the solution so as to maintain it at a temperature of 30°C or below.

26. A method according to any previous claim, comprising cooling the solution so as to maintain it at a temperature of 20°C or below.

27. Smoked e-liquid obtainable by a method according to any of claims 1 to 26.

28. Smoked e-liquid obtainable by a method according to any of claims 1 to 26, having pH 4.5 or greater.

29. Smoked e-liquid obtainable by a method according to any of claims 1 to 26, having pH 5 or greater.

30. Tobacco smoke flavoured e-liquid obtainable by a method according to any of claims 1 to 26.

31 . Apparatus for treating an e-liquid solution to make smoked e-liquid solution, comprising:

a smoking vessel (e.g. pan) holding the e-liquid solution to be treated;

a mixer for mixing contents of the smoking vessel;

a conduit from the output of the smoke chamber to the smoking vessel with an exit for introducing the smoke into the solution, below the surface of the solution; wherein the mixer is adapted to agitate the solution so as to break up the introduced smoke into bubbles.

32. Apparatus according to claim 31 , wherein the mixer is capable of operating so as to create reduced pressure to draw smoke into the solution in the smoking vessel.

33. Apparatus according to claim 31 or 32, comprising a filter for filtering the smoke before it is introduced into the solution.

34. Apparatus according to claim 33, comprising a filter adapted to filter the smoke to reduce its PAH content.

35. Apparatus according to claim 33 or 34 comprising a filter to treat the smoke to selectively remove one or more PAHs that contain 4 or more benzene rings therefrom.

36. Apparatus according to any of claims 33 to 35, wherein the filter is adapted to selectively remove benzo(a)pyrene, benz(a)anthracene and/or dibenz(a,h)anthracene.

37. Apparatus according to any of claims 31 to 36, comprising fuel mixed with filter material.

38. Apparatus according to any of claims 31 to 37, wherein the mixer is adapted to break the smoke into bubbles of average diameter 5mm or less.

39. Apparatus according to claim 38, wherein the mixer is adapted to break the smoke into bubbles of average diameter 2mm or less.

40. Apparatus according to any of claims 31 to 39, wherein the mixer comprises a mixing head in the solution, and the conduit exit is positioned with respect to the mixing head so that the mixer breaks up the introduced smoke into bubbles.

41 . Apparatus according to claim 40, wherein the mixing head comprises a mixing blade, and smoke is introduced in close proximity of the blade.

42. Apparatus according to any of claims 31 to 41 , wherein the mixing head comprises a rotor and a stator and the conduit exit is attached to the stator.

43. Apparatus according to claim 42 wherein the conduit exit is no more than 10cm from the blade of a mixer.

44. Apparatus according to claim 43 wherein the conduit exit is no more than 3cm from the mixer blade.

45. Apparatus according to any of claims 31 to 44, comprising a chimney to vent the smoking vessel to the atmosphere.

46. Apparatus according to claim 45, comprising a unit to scrub off-gas prior to venting.

47. Apparatus according to any of claims 31 to 46, wherein there is no conduit permitting recirculation of off-gas back through the solution.

48. Apparatus according to any of claims 31 to 47, comprising monitoring and control equipment for monitoring the method and adjusting the agitation to reduce to a minimum the smoke bubbles that escape from the solution being smoked.

49. Apparatus according to claim 48, wherein the monitor and controls allows increasing the agitation until no or substantially no smoke bubbles escape and then reducing the agitation until smoke bubbles escaping begins to be noticeable.

50. Apparatus according to any of claims 31 to 49 comprising a cooler to cool the solution during smoking, optionally with a controller to maintain the solution at or below a desired temperature.

51 . Tobacco smoke flavoured e-liquid.

52. Tobacco smoke flavoured e-liquid, made using filtered smoke.