Patent ID: 12187990

DETAILED DESCRIPTION OF THE INVENTION

As shown inFIG.1, the present invention addresses the wort treatment step following lautering (400) and preceding trub separation (500) such as is most often performed in a whirlpool tun. It is clear that a buffer or pre-heating tank can be interposed between a lautering tun and the kettle (1) without changing anything to the present invention. The wort treatment step subject of the present invention is traditionally referred to as a “boiling” step because the wort is traditionally heated above its boiling temperature to sterilize it, terminate enzymatic activity, and convert and/or remove undesired components. In the present process, however, the term “pseudo-boiling” step is used instead because, contrary to the prior art processes, wort is not brought to its boiling temperature at any moment during the treatment time, ttreat.

The pseudo-boiling process of the present invention is meant to replace advantageously the boiling processes disclosed and used to date in the art, with a concomitant substantial reduction of the energy consumption. In particular, after both a boiling and a pseudo boiling step:(a) The wort must be sterilized,(b) the enzymatic activity, must be terminated(c) the amount of alpha acids shall be reduced and replaced by iso-alpha-acids,(d) a substantial amount of S-methylmethionine (SMM) must have been transformed into dimethylsulfide (DMS),(e) haze active proteins and polyphenols must have been coagulated for separation, and(f) unwanted flavour compounds, in particular DMS, shall be removed.

The above objectives (a) to (d) are mostly time-temperature dependent and can be achieved at temperatures above 90° C., with a rate increasing with the temperature. Coagulation of proteins and polyphenols and removal of unwanted volatile flavour components, on the other hand, are substantially accelerated when the interfacial area between liquid and gas is increased. For this reason, it is necessary to bring the wort to boiling in order to generate vapour bubbles which substantially increase the liquid-gas interfacial area, and hence the coagulation rate of haze active proteins and polyphenols, and removal rate of undesired volatile components. This method of boiling wort to increase the liquid-gas interfacial area works but has two major inconveniences:(a) It is strongly energy consuming, and(b) Water evaporation ranges from 4 wt. % for the most economical boiling systems, to 6-10 wt. % and more for more traditional boiling techniques.

Boiling water is very energy consuming. Wort physical heat properties are very comparable to those of water. Latent heat of vaporization of water (and wort) is very high: 2260 kJ/kg. It follows that if the heat required to heat 1 litre of wort by a temperature difference, dT, up to a temperature below the boiling temperature of wort, Tb, is Q=cp dT kJ/kg wherein cp is the specific heat of wort (≃4.19 kJ/kg ° C.), whilst 2260 kJ/kg are required by the system to turn said 1 litre of liquid water into vapour once the temperature of the wort has reached the boiling temperature, Tb. Note that since the boiling temperature of wort (and water) is pressure dependent, the actual value of Tbvaries as a function of the weather and location of the brewery. At atmospheric pressure, Tb=100° C., but it is clear that liquid wort will never reach such temperature in a brewery located in Mexico City or in Lhasa.

Removal of unwanted volatile flavour compounds such as DMS depends on the vapour-liquid equilibrium (VLE) of each volatile with wort. This means that a determined amount of evaporation is needed to reduce the level of an undesired compound to sub-threshold levels. Therefore a minimum evaporation is always required and most recent systems operate with a minimum of 4-6% evaporation, which is still a considerable amount.

To carry out a process according to the present invention, a kettle (1) is required, which is provided with an inlet (1u) suitable for feeding a wort into the kettle and with an outlet (1d) suitable for flowing the wort out of the kettle. Heating means (2) suitable for heating the wort in the kettle must be provided. The heating means are generally in the form of a bundle of parallel jacketed hollow tubes, wherein the wort is circulated through the lumen of the hollow tubes which are heated by a heating fluid circulating in the jackets. The heating means (2) can be located inside the kettle, thus forming an internal boiler kettle as illustrated inFIG.3(a). Due to their very low density these vapour bubbles are the driving force upward through the internal boiler, thereby ensuring a natural convection. In some systems of the prior art, a pump is located below the internal boiler to force wort collected at various points of the kettle to flow through the heating pipes. Though applicable, such forced convection system is not mandatory in the present invention because, as will be discussed below, the sparged gas bubbles create already a forced convection. Alternatively, the heating means (2) can be located outside the kettle, fluidly connected thereto by pipes, thus forming an external boiler kettle as illustrated inFIGS.4(a)&5(a). A pump (8) is usually used to force wort flow through the boiler, Most kettles of the prior art, traditionally used to carry out a wort boiling step fulfill the foregoing requirements,

The equipment required for the present invention requires a gas sparging system (3) suitable for sparging an inert gas into said wort. Although known in the art, such as disclosed in EP875560, few boiling kettles are provided with a gas sparging system. A gas sparging system can be very simple; and may include a circular plate, cylinder or ring provided with a multitude of apertures. The apertures can be through channels, like in a shower head, or they may be the pores of an open pore structure, such as a sintered material (e.g., sintered stainless steel). If the inert gas used is nitrogen, a nitrogen converter is very simple and inexpensive to install, and if CO2is used instead, it is clear that such gas is abundantly available in all breweries. An advantage of the present invention is therefore that it requires no or little modifications to the existing equipment. As shown inFIGS.3(b) and4(b), the gas sparger (3) is preferably located at the bottom of the kettle, so that the gas bubbles may rise to the surface of the wort, fixing on their way up volatiles and haze active proteins. In an alternative embodiment, illustrated inFIG.5(a)&(b), an external boiler kettle is provided with a gas sparging system located at the upstream end of the external boiler with respect to the wort flow direction (in case ofFIG.5, at the bottom of the boiler). The bubbles are forced through the hollow heating tubes (2a) and injected into the kettle together with the wort. For kettles of the internal boiler type, it is preferred that the sparger be located below the heating tubes (2a) and preferably have a largest dimension (diameter in case of a disc, cylinder, or a ring) which is smaller than the largest diameter of the boiler (2). With such configuration, the gas bubbles rising through the hollow tubes (2a) of the internal boiler create a forced convection driving wort through the lumens of the hollow tubes of the boiler. This is very advantageous because, on the one hand, no immerged pump is required to create such forced convection and, on the other hand, the flowing rate of the wort through the hollow heating tubes during the heating stage is higher and more homogeneous compared with natural convection systems at temperature below, Tb, when insufficient vapour bubbles are present to create a natural convection with the risk of locally over-heating wort.

When a kettle provided with an internal boiler (2) is used, a baffle (5) and a deflector-roof (6) are preferably provided on top of the internal boiler in order to channel the flow of rising gas bubbles and wort, redistribute them over the top liquid-air interface of the wort, and reduce the thickness of the foam thus formed to permit better elimination in the air of the volatiles entrained with the bubbles (cf.FIG.3(b)).

Wort is fed to the kettle from a lautering step (400). In some cases, wort is first passed through a buffer or pre-heating tun prior to entering the kettle. The temperature of the wort is generally below 90° C., often comprised between 65 and 85 C. After filling the kettle (1) with wort, an inert gas is sparged into the wort and the latter is concomitantly heated to a treatment temperature, Ta, which is lower than the boiling temperature, Tb, of the wort, as illustrated inFIG.2. When the wort has reached the treatment temperature, Ta, it is maintained at said temperature, Ta, still under flow of said inert gas, for a period of time, ttreat, comprised between 15 and 90 min, preferably, between 20 and 75 min, more preferably between 30 and 60 min. As mentioned above, the inert gas is preferably nitrogen or carbon dioxide, the former being more preferred.

As illustrated inFIG.2, the inert gas flow rate is highest during the heating period of wort to temperature, Ta, and is decreased when the wort is maintained at temperature, Ta. The initial inert gas flow rate can be comprised between 0.05 and 50 m3/h/hl wort, more preferably between 0.1 and 10 m3/h/hl. Once the wort has reached its treatment temperature, Ta, the gas flow rate can be reduced to about 35 to 50%, more preferably between 37 and 45% of the initial value (QN2(0)), of the inert gas sparging flow rate.

The treatment temperature, Ta, according to the present invention is below boiling temperature, Tb, of the wort. In particular, it is preferably greater than 90° C., more preferably greater than 97° C. As discussed above, the rate of several of the reactions required to happen during the pseudo-boiling process are temperature dependent, such as sterilization, termination of enzyme activity, conversion of SMM into DMS, and the like. There is therefore a trade-off temperature value to be found wherein treatment time, ttreat, remains commercially reasonable and energy consumption is below today's levels. This trade off value of the treatment temperature, Ta, is preferably comprised between (Tb-2° C.) and the boiling temperature, Tb, of the wort. It is not excluded to heat the wort at the boiling temperature, Tb, after the treatment time, but in the vast majority of cases it is not necessary, and the excess energy required to boil the wort, even for a short time should be justified by some specific requirements of the treated wort.

As shown inFIGS.3(b)&4(b), an inert gas sparger located at the bottom of the kettle generates a column of gas bubbles. The volatile components present in the wort are thus in equilibrium between gas and liquid phases without need for the wort to boil. As discussed above, the column of bubbles penetrating through the lumens of the hollow tubes of an internal boiler as depicted inFIG.3(b), creates a forced convection independent of temperature, contrary to natural convection which is highly temperature dependent for the creation of sufficient vapour bubbles. On the other hand, inert gas bubbles act like vapour bubbles when surfacing, yielding the same effect as with the latter with respect to elimination of volatiles and coagulation of haze active proteins, but without having to boil and evaporate large amounts of wort. The gas flow is also advantageous because it homogenizes the wort by creating a gas lift system with a central ascending flow and a lateral descending flow, as illustrated by the black arrows inFIGS.3(b)&4(b).

After the pseudo-boiling process of the present invention, wort can be fed to a whirlpool tun or the like for separating trub from clear wort, and thence proceed to fermentation (700), maturation (800), filtering (900) and packaging (1000) of the thus produced beer exactly in the same way as in the conventional brewing processes.

Example 1

5.4 hl wort issued from a lautering step was divided into two batches of 2.7 hl each. One was fed to a traditional boiling step, and is used as reference (=REX.1) and the other was treated with a pseudo-boiling process according to the present invention (=EX.1). The two batches were treated in identical internal boiler kettles (1), but the gas sparger (3) was not activated in the reference batch, REX1.

Boiling Process of REX.1

As wort level in the kettle reached the internal boiler, heat exchange occurred and wort was heated up to 100° C., whence wort started boiling intensively with high turbulences and was maintained in such state of ebullition during a treatment time, ttreat(REX1)=60 min. Dense water vapour was observed throughout the treatment period.

Pseudo-Boiling Process of EX.1

From the moment the spray head was below the level of wort, the sparging process was started with nitrogen at a flow rate of 0.1 m3/h/hl. In order to ensure sufficient homogenization of the wort while heating up, forced convection is an absolute need during this phase. In the beginning, the maximum nitrogen flow rate is therefore applied.

When the heating proceeds towards the treatment temperature, Ta=98.5° C., the nitrogen flow rate can be decreased regularly until a flow rate of 40% of the initial value is obtained at 98° C. The magnitude of nitrogen flow has to be adjusted to the boiling-like state of the wort at 98.5° C. In this 'dynamic system, it appears that the wort is boiling already, yet from a thermodynamic point of view, such is not the case at all. The mixture of nitrogen and wort vapours ensures a very vigorous circulation. Hop addition can occur at any stage of the heating up phase. In Ex1 and REX1 hop was added as soon as the kettle was filled with wort.

The wort temperature was held at about 98.5° C., thereby maintaining the pseudo-boiling-like state during a treatment time, ttreat(EX1)=60 min. During the entire process, the wort appeared as if it were boiling very intensively with high turbulences like in the REX1, but by contrast, the rising vapours were very thin, resulting in very limited evaporation. Unwanted volatiles could thus be evacuated without an extensive evaporation rate.

Rising nitrogen bubbles also provide an interface for the orientation of denatured proteins responsible inter alia for haze formation in the beer, thus enhancing the coagulation thereof. Therefore coagulation can take place without attaining the boiling temperature since the nitrogen bubbles replace vapour bubbles.

Simultaneously, the bubble column provides forced convection, in the boiling kettle. Therefore intensive heating is not needed in order to create vapour bubbles as required for activating the thermosyphon principle in internal boiler kettles with natural convection. It is sufficient to provide enough heating fluid, such as steam, in the jackets of the hollow tubes (2a) forming the boiler (2) to only maintain the required temperature, Ta=98.5° C.

Beer Production

The batch treated according to the present invention (=EX1) registered an evaporation rate of 2.8 wt. %, whilst the batch used as reference (=REX.1) registered an evaporation rate of 10.8 wt. %. When comparing the pseudo-boiling process of EX.1 with the conventional wort boiling process of REX.1, it is imperative that all other beer production parameters are kept constant throughout the entire production process. For this reason, upon feeding the thus treated wort to a whirlpool tun (500), an amount of hot water (76° C.) was added to the wort of REX.1 in order to compensate for the density difference between the 2 worts due to the differing evaporation rates. After cooling, aerated wort was pitched with equal amounts of yeast slurry and the temperature profiles were kept equal during fermentation (700). After filtration (900) the final beers were bottled (1000) and a portion thereof subjected to accelerated (either thermal or oxidative) aging, prior to analysis.

Results

General quality parameters of beers produced from the worts treated in EX.1 and in REX.1 are listed in Table 1. The difference in evaporation is spectacular: 8% difference between 10.8 wt. % for REX.1 and 2.8 wt. % for EX.1. No significant changes in foam stability or haze stability could be observed. The haze stability of the beer of EX.1 was even slightly better than the reference. The colour of the EX.1 was substantially better than the one of REX.1 and the TBA increase of EX.1 was 28% lower the one of REX.1.Foam stability was determined according to the NIBEM method described. The NIBEM Institute has set standards for the measurement of the foam stability. The NIBEM Foam Stability Tester measures the foam collapse time over a distance of 30 mm and is expressed in seconds.Haze was measured using a Turbidity Meter which measures the scattered light caused by particles and incorporates the latest standards from MEBAK (Mitteleuropäische Brautechnische Analysekommission):90° measuring angleRed light 650±30 nmFormazin calibration standardParticles smaller than 1 μm, such as proteins, mainly cause scattered light and are measured under 90°. Particles larger than 1 μm, such as diatomaceous earth and yeast, mainly cause forward-scattered light and are measured under 25°. A sample (cuvette or bottle) is placed in the measuring chamber, which is filled with water. The automatic measurement proceeds, positioning the sample and rotating it, making 100 measurements, and calculating the average value.The thiobarbituric acid number method (TBA) was carried out as described in Grigsby, J. H. and Palamand, S. R.Studies on the Staling of beer: the use of2-thiobarbituric acid in the measurement of beer oxidation, ASBC J. (1975) 34 (2), 49-55. Five ml of a TBA solution (288 mg of thiobarbituric acid in 100 ml acetic acid (90%)) was added to 10 ml of wort in sealed pyrex tubes (in duplicate). The mixtures were kept in a water bath at 70° C. for 70 minutes. The samples were then cooled on ice. The foregoing thermal treatment permits the formation of complexes between TBA and hydroxymethylfurfural (HMF), the presence of the latter in the wort resulting from Maillard reactions, well known to the persons skilled in the art. The presence of HMF-TBA complexes can easily be identified and quantified by spectrophotometry as they are characterized by a strong absorption at a wavelength of 448 nm. If necessary, the samples were diluted in order to obtain a value in the linear range of the spectrophotometer. As blank measurement, absorption of the same wort with TBA but with no thermal treatment was measured at the same wavelength. The TBA value could then be calculated as follows TBA=10×(D×A448(sample)−A448(blank)), wherein D is a dilution factor, :A448(sample) and A448(blank) are the absorptions measured at 448 nm of the thermally treated wort+TBA solution samples and blank (wort+TBA solution not thermally treated), respectively.

TABLE 1Comparison of quality parameters of beerbrewed with wort according to EX1&REX. 1ParameterEX1REX1evaporation, (wt. %) ()2.810.83foam stability (NIBEM), (s) ()269274Haze (after 3 days at 60° C.), (EBC) ()0.510.58Haze (fresh beer), (EBC) ()0.291.01colour, (EBC) ()7.558.75thermal load during (pseudo) boiling, (ΔTBA) ()7.910.92-furfural (ppb) ()150180phenylacetaldehyde (ppb) ()122140linalool (ppb) ()13587R = ΔDMS/% evaporation (ppb DMS/% vapour) ()11.44.8() high value desired,() low value desired

The evaporation efficiency of a wort boiling system is mostly evaluated by the DMS removal during (pseudo-) boiling as a function of amount of wort evaporation. Samples were taken at the beginning (t=0 min), in the middle (t=30 min), and at the end (t=60 min) of treatment time, ttreat=60 min period. The amounts of DMS measured at different times are plotted inFIG.6. At time, t=0 min, the wort treated according to the present invention (=EX.1, black circles)) contained 38 ppb DMS whilst at the same time, the wort which just reached its boiling temperature according to a conventional boiling process (REX.1, white circles) contained 59 ppb. This is explained because, whilst the two batches of wort had exactly the same content of 65 ppb of DMS upon entering the kettle (1), during the heating up stage of the wort to their respective treatment temperatures, Ta, DMS was already being actively removed by the nitrogen bubbles sparged in the wort during said stage (cf.FIG.2), whilst in the absence of a sparging gas in REX.1, DMS content did not decrease significantly during the heating stage. After a treatment time, ttreat, of 60 min, the amounts of DMS left in the two wort batches were comparable with 6 ppb DMS in EX.1 and 7 ppb DMS in REX.1. The evaporation efficiency, R, can be characterized by the ratio of the amount of DMS removed during the (pseudo-) boiling stage, to the amount of water evaporated during the same time, R=ΔDMS/% evaporation, yielding 11.4 ppb DMS/% vapour for EX.1, versus 4.8 ppb DMS/% vapour for REX.1, i.e., EX.1 yields an evaporation efficiency 2.4 times higher than REX.1.

Beer Quality

In order to gain insight in the flavour stability of the produced beers, bottles of fresh beer were stored for 3 days at 60° C. and the amounts of furfural and phenylacetaldehyde were measured for beers of EX.1 and REX.1 (cf. last rows of Table 1). Furfural is generally regarded as an indicator compound for heat-induced flavour damage and phenylacetaldehyde, one of the Strecker aldehydes, is also suspected to be involved in flavour stability. Both compounds were found in higher amounts in fresh and aged reference beers. This was not unexpected, since these compounds are related to the total heat load, quantified by the TBA-value. Remarkably, the concentration of linalool and other hop flavour compounds (not listed) was up to 80% higher in the beer of EX.1 than in the REX.1 beer (cf. last row of Table 1). These terpenoid compounds are known to contribute positively to the overall beer flavour. It can be assumed that nitrogen bubbles are (fortunately) less efficient in removing such terpenoids than vapour bubbles.

The beers were also evaluated by a trained degustation panel. The fresh beer of EX.1 had a high overall score of 7.1 comparing to the reference beer scoring 6.6. This is certainly, at least in part, due to the higher retention of beneficial hop volatiles or the reduced bitterness in the beer of EX.1. After aging, the beer of EX.1 scored slightly higher than the reference beer of REX.1 with 3.9 vs. 3.5, respectively. The panel concluded that the intensity of overall aging, Maillard components and aldehydes was slightly higher in the reference beer (=REX.1), while the old hop flavour became more apparent in the beer of the present invention (=EX.1). Strikingly, the sulfury, hay-like aging flavour was substantially more dominant in the reference beer (REX.1). Apparently, sulfury flavours or their precursor compounds were driven off more completely by the pseudo-boiling process with nitrogen sparging of the present invention (=EX.1) than by the conventional boiling process of the reference example, REX.1.

Example 2

The boiling experiment carried out in a pilot plant of EX.1 was repeated in a full scale brewhouse equipment. After pseudo-boiling wort during a time, ttreat, of 60 min according to the present invention, the evaporation rate was 1.5 wt. % (=EX.2). A conventional boiling process of the type used in REX.1 using an internal boiler kettle with natural convection (=REX.2) yielded an evaporation rate of 8 wt. %. The same experiment was carried out with an internal boiler kettle with forced convection (i.e., wherein wort is driven through the boiler heated tubes by a pump) (=REX.3) yielding an evaporation rate of 5 wt. %. Table 2 compares the energy consumptions of the three (pseudo-) boiling processes of EX.2, and REX.2&3. It can be seen that the pseudo-boiling process of the present invention consumes only 19% of the energy consumed by conventional boiling process with natural convection (REX.2) and about a third of the energy consumed by a boiling process with forced convection (REX.3).FIG.7compares graphically the absolute and relative energy consumptions of EX.2 (black column) and REX.2&3 (white columns).

TABLE 2comparison of energy consumption betweenboiling and pseudo-boiling processesREX. 2REX. 3internalinternalboilerboilerEX. 2with naturalwith forcedINVconvectionconvectionevaporation (wt. %)1.585energy consumption (kJ/hl)3,38718,06311,290energy (kWh/hl)0.945.023.14relative energy consumption19%100%63%(relative REX. 2) (%)consumption for 400,000 hl3762,0071,254(MWh)

The pseudo-boiling process of the present invention is an advantageous alternative to conventional wort boiling yielding beer of comparable quality with over 80% energy saving. All observed quality parameters of the produced worts and beers according to the present invention were comparable or better than their corresponding reference beers, while the evaporation rate of the pseudo-boiling process was only 20 to 30% of the reference evaporation rate. The potential energy savings of the process of the present invention are very high (up to 4 kWh/hL), which is an asset, since energy becomes more expensive every day.

The pseudo-boiling process of the present invention combines the advantages of wort boiling systems with forced convection, hot holding or stripping and provides an excellent means to meet the requirements of wort boiling:Evacuation of volatiles is enhanced without the need for extensive evaporation and thus, energy.Forced convection is ensured by a continuous upward stream of nitrogen bubbles (gas lift). The convection is therefore completely independent of the heating intensityNo boiling temperature is needed. Hot holding is sufficient.Coagulation of proteins occurs without the presence of vapour bubbles. The small nitrogen bubbles provide a large interface, which allows the denatured proteins to coagulate. The results of the final beers show good haze and foam stability (cf. Table 1).