PROCESS FOR TREATING WORT

Abstract

The present invention provides a process for treating a wort composition in a kettle, said method providing a significant energy saving compared to existing wort treatment processes. In particular, the process includes a hot-hold step for the wort, followed by gas sparging at elevated temperatures.

Claims

1. A process for treating a wort composition in a kettle, said method comprising the steps of: (a) providing: a kettle provided with an inlet suitable for feeding a wort composition into the kettle and with an outlet suitable for flowing the wort out of the kettle; heating means; a gas sparging system suitable for sparging a gas into said wort; (b) adding wort from a mash separating step into said kettle through the inlet; (c) heating said wort to a target temperature between 80 and 96 C.; (d) maintain an average target temperature between 80 and 96 C. for a period of 12-45 minutes, and during which the wort composition does not reach its boiling point, and during which period gas sparging of less than 10 g/Hl/Hr, preferably no gas sparging, takes place; (e) raising the temperature of the wort composition to a target temperature of between 97 C. and 99 C.; (f) sparging a gas through the wort composition at an average rate of 80-350 g/Hl/Hr while maintaining an average target temperature of between 97 C. and 99 C. for a period of between 15 minutes and 75 minutes; and during which the wort composition does not reach its boiling point; and (g) transferring the treated wort composition to a trub separation step through the kettle outlet.

2. The process according to claim 1, wherein in step (c), the wort is heated to a target temperature between 93 and 95.5 C., preferably between 94.5 and 95.5 C.

3. The process according to claim 1, wherein in step (d) the average target temperature is between 93 and 95.5 C. preferably between 94.5 and 95.5 C.

4. The process according to claim 1, wherein the process step (d) is carried out for a period of 15-20 minutes.

5. The process according to claim 1, wherein the process step (d) involves no gas sparging.

6. The process according to claim 1, wherein the process step (e) comprises raising the temperature of the wort composition to a target temperature of between 97 C. and 99 C., preferably between 98 C. and 99 C.

7. The process according to claim 1, wherein the process step (f) comprises sparging a gas through the wort composition at an average rate of 120-220 g/Hl/Hr, preferably 190-210 g/Hl/Hr, more preferably at about 200 g/Hl/Hr.

8. The process according to claim 1, wherein the process step (f) is carried out for a period of between 55 minutes and 65 minutes, preferably about 60 minutes.

9. The process according to claim 1, wherein the wort composition in step (c) is heated to the target temperature at a rate of between 0.2 C. and 1 C. per minute, preferably between 0.4 C. and 0.75 C. per minute, most preferably about 0.5 C. per minute until the target temperature is met.

10. The process according to claim 1, wherein once step (d) is completed, the wort composition is heated to the target temperature of step (e) at a rate of between 0.2 C. and 1 C. per minute, preferably between 0.4 C. and 0.75 C. per minute, most preferably about 0.5 C. per minute until the target temperature is met.

11. The process according to claim 1, wherein the sparged gas is selected from CO.sub.2, N2 and air, and combinations thereof, preferably CO.sub.2.

12. The process according to claim 1, wherein the wort composition at the end of step (f) contains less than 150 ppb of combined SMM and DMS, more preferably less than 100 ppb, more preferably less than 75 ppb.

13. The process according to claim 1, wherein the wort composition exiting step (f) of the process achieves a DMS (dimethyl sulphide) concentration of less than 150 ppb, more preferably less than 100 ppb, more preferably less than 50 ppb, more preferably less than 20 ppb.

14. The process according to claim 1, wherein the process steps (a) to (f) result in less than 2%, more preferably less than 1.5%, more preferably 0.8-1.2% evaporation of water based on a weight of the wort composition prior to treating.

Description

BRIEF DESCRIPTION OF THE FIGURES

[0079] For a fuller understanding of the nature of the present invention, reference is made to the following detailed description taken in conjunction with the accompanying drawings in which:

[0080] FIG. 1: shows the various steps of a brewing process;

[0081] FIG. 2: Schematic of process steps of the present invention;

[0082] FIG. 3: Shows a first embodiment of an internal boiler kettle suitable for the present invention, (a) empty and (b) filled with wort and with gas being sparged therein;

[0083] FIG. 4: Shows a second embodiment of an external boiler kettle suitable for the present invention, (a) empty and (b) filled with wort and with gas being sparged therein;

[0084] FIG. 5: Shows a third embodiment of an external boiler kettle suitable for the present invention, (a) empty and (b) filled with wort and with gas being sparged therein; and

[0085] FIG. 6: Shows the combined SMM and DMS content of the process of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

[0086] As shown in FIG. 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.

[0087] 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:

[0088] (a) The wort must be sterilized,

[0089] (b) the enzymatic activity, must be terminated,

[0090] (c) the amount of alpha acids shall be reduced and replaced by iso-alpha-acids,

[0091] (d) a substantial amount of S-methylmethionine (SMM) must have been transformed into dimethylsulfide (DMS),

[0092] (e) haze active proteins and polyphenols must have been coagulated for separation, and

[0093] (f) unwanted flavour compounds, in particular DMS, shall be removed.

[0094] The above objectives (a) to (d) are mostly time-temperature dependent and can be achieved at temperatures above 80 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:

[0095] (a) It is strongly energy consuming, and

[0096] (b) Water evaporation ranges from 4 wt. % for the most economical boiling systems, to 6-10 wt. % and more for more traditional boiling techniques.

[0097] Boiling water is very energy consuming. Wort physical heat properties are very comparable to those of water.

[0098] 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.

[0099] 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 in FIG. 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 in FIGS. 4(a) and 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,

[0100] 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 CO.sub.2 is 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 in FIGS. 3(b) and 4(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 in FIG. 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 of FIG. 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 overheating wort.

[0101] 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)).

[0102] Wort is fed to the kettle from a mash separating step, such as 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 80 C., After filling the kettle (1) with wort, it is heated to a target temperature of between 94.5 and 95.5 C., and this temperature is maintained for a period of 15 minutes, and during which the wort composition does not reach its boiling point. Preferably, no gas sparging takes place during this phase of the process. After this holding phase is carried out, the temperature of the wort composition is increased to a target temperature of between 98 C. and 99 C. When this temperature is reached, a gas is sparged through the wort composition at an average rate of 200 g/Hl/Hr while maintaining an average target temperature of between 98 C. and 99 C. for a period of about 60 minutes; and during which the wort composition does not reach its boiling point. Once this step has been completed, the wort composition is transferred to a trub separation step.

[0103] As illustrated in FIG. 2, this shows an embodiment illustrating the process of a preferred embodiment the present invention. In the first pre-heating phase, the temperature is raised at a rate of 0.6 to 1.2 C./min until the temperature reaches about 3 C. below the natural boiling temperature of the wort. The wort composition is then enters the hot stand phase, where the temperature is maintained at this temperature. The temperature is then raised again to about 1.5 C. below the natural boiling temperature of the wort, and is held there for a period of time during which the composition is sparged with an inert gas. The volatile materials, such as SMM and DMS are stripped from the composition during this part of the process.

[0104] During all of these process steps, the exit temperature of the external heater is kept above that of the wort body composition. This is because some of the heat is lost to the process (radiation, sparging, etc.).

[0105] As shown in FIGS. 3(b) and 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 in FIG. 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 in FIGS. 3(b) and 4(b).

[0106] 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.