IE20020781A1 - A stout manufacturing process - Google Patents

Abstract

A stout manufacturing process includes delivering preset quantities of malt, roast material which includes roast barley and water to a mash tun (45). The materials are mixed in the mash tun (45) to prepare a sweet wort. The sweet wort is delivered through a lauter tun (46) for removing solid materials. Downstream of the lauter tun (46) hops are added to the sweet wort and boiled with the sweet wort in a wort copper vessel (48) to prepare a hopped wort. The hopped wort is cooled in a heat exchanger (52) to about 18° C and delivered through a cold wort line (53) into fermenting vessel (54). Sterile air and yeast are injected into the cooled hopped wort in the cold wort line (53). The mixture in the fermenting vessel (54) is fermented in a controlled manner to form a stout which is then matured in a storage vessel (58) at a selected temperature and pressure. The stout is centrifuged (60) to remove solid materials and the thus clarified stout is stored in a bright stout tank (62) from where it is delivered for conditioning (64,66) and packaging (68) as required. <Figure 1>

Description

"A stout manufacturing process** This invention relates to a brewing process and in particular to a brewing process for manufacturing stout.

In the prior art GB 1060722 discloses a method of brewing beer in a rapid fermentation process by combining in a fermenting vessel oxygenated wort with a relatively high concentration of yeast at the start of fermentation and carrying out controlled agitation of the fermenting mixture for uniform distribution of yeast throughout the wort during the fermenting period. In WO 99/27070 there is disclosed a method for making a beer flavour concentrate and using the beer flavour concentrate to produce a beer product through the addition of a diluent of water, carbon dioxide and alcohol. A stout brewing process is described in WO 97/44436 and BE 1001787A discloses a stout making process which primarily relates to the control of carbon dioxide and nitrogen levels in the stout. 0 The present invention is directed towards providing an improved stout manufacturing process for producing a high quality stout product.

Statements of Invention According to the invention there is provided a stout brewing process including the steps: delivering preset quantities of malt, roast material which includes roast barley and hot water to a mash tun, mixing the material in the mash tun for preparing a brew, preparing a sweet wort from the brew by converting starch in the brew to sugar, delivering the brew to a lauter tun, OPEN TO PUBL'C INSPECTION UNDER SECTION 28 AN L RULE 23 JNLMo-d2-2-I IE 0 2 0 7 β 1 - 2 removing solid material from the sweet wort, delivering the sweet wort to a wort copper vessel, adding hops to the sweet wort and boiling the sweet wort with the hops to prepare a hopped wort, cooling the hopped wort to a temperature in the range 17°C to 19°C, delivering the cooled hopped wort to a fermentation vessel through a cold wort line, injecting sterile air in a controlled manner into the hopped wort as it is delivered through the cold wort line, adding a selected yeast to the hopped wort in the cold wort line as the hopped wort is delivered through the cold wort line, said yeast being added to the hopped wort between the air inlet and the fermentation vessel, fermenting the mixture in the fermenting vessel for a preset period to produce stout, maintaining an average fermentation temperature in the range 19* C to 21 * C over the first 24 hours of fermentation, delivering the stout from the fermenting vessel to a storage tank and storing the stout at a temperature in the range -O.5°C to +0.5°C for a period of between 3 days and 10 days whilst maintaining zero gauge pressure in the storage tank above the stout, delivering the stout from the storage tank to a centrifuge, centrifuging the stout to remove solid material, delivering clarified stout from the centrifuge to a bright stout tank, maintaining the temperature of the stout at less than or equal to 2°C during centrifuging and transfer to the bright stout tank.

IE 0 2 0 7 8 1 - 3 In one embodiment of the invention the process includes the steps of delivering a number of brews to the fermentation vessel over a period of less than 24 hours and adding the total quantity of yeast required for all said brews during delivery of the first brew to the fermentation vessel.

In another embodiment, the process includes the step of maintaining the dissolved oxygen content of the stout at no more than 0.2 mg per litre.

In a further embodiment, the process includes the steps of:delivering the stout from the bright stout tank to a buffer tank at an inlet of a packaging line, conditioning the stout during transfer of the stout from the bright stout tank to the buffer tank for controlling the levels of carbon dioxide and nitrogen in the stout to pre-desired concentrations.

Preferably, the process includes the step of controlling the carbon dioxide content to within the. range of 0.13% to 0.59% by weight. The nitrogen content of the stout is preferably controlled in the range 25 to 55 mg per litre.

Detailed Description of the Invention The invention will be more clearly understood by the following description of some embodiments thereof given by way of example only, with reference to the accompanying drawings, in which; Fig. 1 is a schematic illustration of a stout brewing process according to the invention, Fig. 2 is a schematic illustration of portion of apparatus for carrying out the process of the invention; and IE 0 2 0 / β 1 - 4 Fig. 3 is a schematic view of portion of the apparatus for carrying out the brewing process of the invention.

Malt material is received from a supplier. The malt material comprises two or more brewing varieties of barley selected from two-rowed spring barley, two-rowed winter barley and six-rowed winter barley. Preferably no one of the selected varieties should comprise more than 60% of the malt blend. While all the barley varieties may be selected from spring barley varieties it is desirable that winter varieties of barley should not comprise more than 50% of the malt blend. After carrying out a friability check on each batch of malt material received from a supplier to confirm the quality of the malt material is acceptable the malt material is discharged into an intake hopper. The malt material is then discharged through a series of screens to remove unwanted foreign matter if any is present. At least one screen will incorporate magnets to attract and remove metal objects should they be present in the supply batch. Dust extractors are also provided at suitable locations. The screened malt material is then delivered to one of a number of malt storage silos awaiting use on demand.

When required the malt material is delivered from a malt storage silo to a feed hopper 10 (Fig. 2). The malt material is then discharged from the feed hopper 10 through a screen 11 and delivered into a weigher 12. An elevator conveyor 14, having an inlet 15 and an outlet 16, takes the malt material from the weigher 12 and delivers it via associated feed conveyors 17,18 to a malt day bin 20.

The roast material is prepared from a blend of roast barley and chocolate malt. Preferably roast barley comprises at least 60% of the roast material. Preferably the blend comprises about 60% roast barley and 40% chocolate malt. This amount of roast barley has been found to advantageously aid head retention in the finished stout product. Ideally, the roast material should have a moisture content of less than or equal to 4.5%.

The roast material, comprising the roast barley and chocolate malt, is delivered from a storage silo by means of an air lift, that is a pneumatic conveyor, to a roast material day bin 22. The roast material may alternatively if required be delivered from bags - 5 IE 0 2 0 7 β 1 via a roast material elevator conveyor 23 to the roast material day bin 22. Said roast material elevator conveyor 23 has an inlet 24 and an outlet 25 which discharges into the roast material day bin 22.

Selected quantities of malt material and roast material for a particular production run are collected in the malt day bin 20 and the roast material day bin 22. The roast material should comprise 10% by weight of the combined malt and roast material. Malt material from the malt day bin 20 and roast material from the roast material day bin 22 are discharged from the day bins 20, 22 onto a discharge conveyor 27. An elevator conveyor 28 has an inlet 29 for reception of material from the discharge conveyor 27 at an outlet 30 which discharges the material onto a feed conveyor 31 which in turn delivers the material to a mill supply hopper 32.

Malt and roast material are delivered together through a mill 34 having three pairs of milling rollers arranged sequentially to crush the malt and roast material in a controlled manner to achieve a desirable crush characteristic for the material. Grist taken from the mill 34 is sampled regularly to ensure this desirable crush characteristic is maintained and the gaps between the pairs of mill rollers are adjusted if necessary. Grist from the mill 34 is delivered to a grist hopper 36 which feeds the grist material into a grist bin 37. A screw conveyor 38 at an inlet of the grist bin 37 evenly distributes the grist material throughout the grist bin 37. A discharge conveyor 40 at an outlet of the grist bin 37 delivers the grist material to an elevator conveyor 41 having an inlet 42 for reception of the grist material and an outlet 43 which delivers the grist material to a mash tun 45.

The grist material, comprising the crushed malt and roast material, and heated water are delivered together evenly in proportion throughout the filling period into the mash tun 45. In this regard it is useful to provide a pre-masher in which the water and grist material are run together before delivery into the mash tun 45. The ratio of water to grist material is approximately 3:1 by weight. For example 190 hectolitres of water is combined with 6 tonnes of grist material. The water will be heated to about 68" C or 69" C such that when mixed with the malt and roast material the temperature of the mixture will be 65" C.

IE 0 2 0 7 e 1 - 6 The malt, roast material and hot water are stirred for mixing in the mash tun 45 to prepare a brew. The mash material within the mash tun 45 is maintained at a temperature of about 65" C during a filling period of about 20 minutes whilst mixing the materials in the mash tun 45.

Then the‘mash is allowed to rest for about 75 minutes keeping the temperature in the range 62" C to 68" C and preferably at about 65 C. After resting the mash is gradually heated to 75" C over a period of about 15 minutes and then held at a temperature of 75" C for a period of about 5 minutes. It is desirable to minimise the agitation of the mash to minimise air ingress into the brew, whilst at the same time maintaining a continuous slow stirring of the brew within the mash tun 45. The starch in the brew is converted to sugar thus preparing a sweet wort.

The brew is transferred from the mash tun 45 to a lauter tun 46. Within the lauter tun 46 solid material such as malt and roasted barley grains are removed from the sweet wort. The lauter tun 46 has a perforated bottom through which the sweet wort can run but which retains the solid material. The sweet wort is delivered to a wort copper vessel 48. When the sweet wort has drained to the wort copper vessel 48 sparging of the remaining solid material is carried out to leach out the remaining sweet wort from the solid material. Sparge water at a temperature of about 78’ C is sprayed onto the solid material in the lauter tun 46 and leaches down through the solid material collecting sweet wort which is delivered to the wort copper vessel 48. It is important to regularly sample the hot wort draining from the lauter tun 46 and to stop draining hot wort from the lauter tun 46 when the hot wort drops to 0.8" Plato. During sparging an hydraulic raking system in the lauter tun draws knives or tines through the solid material.

Within the wort copper vessel 48 the sweet wort is boiled with hops to prepare a hopped wort. The hop material mixed with the sweet wort comprises a blend of hop pellets and hop extract. These provide a balance of aroma and bitterness components. The hops comprise between 40% and 60% hop pellets and between 40% and 60% hop extract as a percentage alpha acid content. Preferably the hops are added to the sweet wort at the start of the wort boiling step at a minimum temperature of 95" C. The sweet wort and hops are boiled for a period of about 90 IE 0 2 07 8 1 - 7 minutes to form a hopped wort. During the boiling period approximately 10% of the volume of the wort will be evaporated. An external heating system is used in which the wort is drawn from the wort copper vessel 48 through a shell and tube heat exchanger and recirculated back to the wort copper vessel 48.

Before boiling the pH of the wort is determined. It is desirable to maintain the pH of the wort in the range 5.1 to 5.3. To this end, if the measured pH of the wort falls outside this range then a food grade acid can be added to the wort if required at the beginning of boiling to bring the wort within the desired pH range.

After boiling hop residues are removed from the hopped wort. This is achieved by pumping the hopped wort into a whirlpool vessel 50. The whirlpool vessel 50 is cylindrical and the hopped wort is pumped tangentially into the vessel 50 at the side wall so that the hopped wort swirls around an interior of the side wall and the hop residues collect within the centre of the whirlpool vessel 50. The pumping of the hopped wort into the whirlpool vessel 50 may take in the order of 20 minutes and the hopped wort is then allowed a rest period of about 45 minutes in the whirlpool vessel 50.

The hopped wort is then drawn away from a side wall of the whirlpool vessel 50 and delivered through a plate heat exchanger 52 for cooling the hopped wort to a temperature of about 18’ C. The emptying of the whirlpool vessel 50 is carried out over a period of about 1 hour.

The cool hopped wort is delivered through a cold wort line 53 to a fermentation vessel 54. Sterile air is injected into the hopped wort in a controlled manner as it is delivered through the cold wort line 53.

The sterile air is delivered from air compressors through air filters and is injected into the cold wort line 53 through a sintered candle which is mounted in the cold wort line 53. It will be noted that the air is injected contra flow to the wort flow through the cold wort line 53 at a rate of about 9 milligrams per litre.

A selected yeast is also added to the hopped wort in the cold wort line 53 as the IE 02 07 8 1 - 8 hopped wort is delivered through the cold wort line 53. The yeast is added to the hopped wort between the air inlet and the fermentation vessel 54. The yeast is added at a rate of 0.4 litres yeast solution per hectolitre of wort. It will be noted also that all of the yeast is injected at the start of the wort transfer to the fermentation vessel 54. For example if a brew comprises 300 hectolitres of wort all the yeast is injected into the first 50 hectolitres of wort.

A number of brews may be delivered to the fermentation vessel 54 over a period of up to 24 hours and more typically in less than 8 hours. In this case the total quantity of yeast required for all of the brews is added during delivery of the first brew to the fermentation vessel 54.

It is desirable to regulate the dissolved oxygen content of the hopped wort such that it is maintained within the range 6 to 8 milligrams per litre at the inlet of the fermentation vessel 54.

The material in the fermentation vessel 54 is allowed to ferment over a number of days, typically 3 days. The fermentation temperature should be kept at about 20’ C over the fermentation period.

Stout formed as a result of the fermentation is then blended 56 and stored in a storage vessel 58 for a desired time period to allow it to mature. It will be noted that in some cases the fermenting vessel 54 may also form the maturing vessel 58 if required. The stout is stored in the storage vessel 58 at a temperature of about 0’ C for a period of between 3 and 10 days. The pressure in the storage vessel 58 above the stout is maintained at zero gauge pressure during this maturing step.

Finings are added to the stout in the storage vessel 58 to assist in sedimentation, said finings being added at the start of the maturation process. The finings are added at a rate of 2 to 3 grams per hectolitre of stout. The finings may be dosed proportionally into the stout during transfer from the fermenting vessel 54 to the maturing vessel 58 or directly added to the storage vessel 58.

After maturation the stout is delivered from the storage vessel 58 to a centrifuge 60 - 9 IE 0 2 0 7 g j for filtering any remaining solid material from the stout. Clarified stout discharged from the centrifuge 60 is delivered to a bright stout tank 62. Throughout the transfer of the stout from the storage vessel 58 to the bright stout tank 62 the temperature of the stout is maintained at or below 2° C.

When ready for packaging in kegs, bottles or cans the stout is delivered from the bright stout tank 62 through a pasteurising station 64 at which the stout is pasteurised at a temperature in the order of 69-70°C. Thereafter the stout is conditioned for controlling the levels of carbon dioxide and nitrogen in the stout to pre-desired concentrations. The carbon dioxide content is maintained within the ranges 0.13% to 0.59% by weight and the nitrogen content is maintained within the range 25-55 milligrams per litre. After conditioning the stout is filled into kegs at a kegging station 68.

It will be noted that the conditioning may alternatively be done in a two-stage process. In this case a coarse conditioning is carried out immediately after centrifuging the stout with a subsequent fine tuning of the carbon dioxide and nitrogen levels to the desired concentrations immediately before kegging if required.

It will be noted also that the alcohol content of the stout may be controlled to the required levels after centrifuging and before delivery of the stout to the bright beer tank. The stout at the centrifuge will have too high an alcohol content - typically in the order of 5.2% alcohol by volume and this will need to be lowered by dilution with water to 4.0% alcohol by volume.

The invention is not limited to the embodiments hereinbefore described which may be varied in both construction and detail within the scope of the appended claims.

Claims (8)

1. A stout brewing process including the steps: delivering preset quantities of malt, roast material which includes roast barley and hot water to a mash tun, mixing the material in the mash tun for preparing a brew, preparing a sweet wort from the brew by converting starch in the brew to sugar, delivering the brew to a lauter tun, removing solid material from the sweet wort, delivering the sweet wort to a wort copper vessel, adding hops to the sweet wort and boiling the sweet wort with the hops to prepare a hopped wort, cooling the hopped wort to a temperature in the range 17°C to 19°C, delivering the cooled hopped wort to a fermentation vessel through a cold wort line, injecting sterile air in a controlled manner into the hopped wort as it is delivered through the cold wort line, adding a selected yeast to the hopped wort in the cold wort line as the hopped wort is delivered through the cold wort line, said yeast being added to the hopped wort between the air inlet and the fermentation vessel, fermenting the mixture in the fermenting vessel for a preset time period to produce stout, maintaining an average fermentation temperature in the range 19°C to 21 °C over the first 24 hours of fermentation, IE 0 2 07 β 1 - 11 delivering the stout from the fermenting vessel to a storage tank and storing the stout at a temperature in the range -0.5°C to +0.5°C for a period of between 3 days and 10 days, whilst maintaining zero gauge pressure in the storage tank above the stout, delivering the stout from the storage tank to a centrifuge, centrifuging the stout to remove solid material, delivering clarified stout from the centrifuge to a bright stout tank, and maintaining the temperature of the stout at less than or equal to 2°C during centrifuging and transfer to the bright stout tank.

2. A process as claimed in claim 1 including the steps of delivering a number of brews to the fermentation vessel over a period of less than 24 hours and adding the total quantity of yeast required for all said brews during delivery of the first brew to the fermentation vessel.

3. A process as claimed in claim 1 or claim 2, including the step of maintaining the dissolved oxygen content of the stout at no more than 0.2 mg per litre.

4. A process as claimed in any preceding claim, including the steps:delivering the stout from the bright stout tank to a buffer tank at an inlet of a packaging line, and conditioning the stout during transfer of the stout from the bright stout tank to the buffer tank for controlling the levels of carbon dioxide and nitrogen in the stout to pre-desired concentrations.

5. A process as claimed in claim 4, wherein the process includes the step of controlling the carbon dioxide content to within the range 0.13% to 0.50% by IE 0 2 07 β 1 - 12 weight.

6. A process as claimed in claim 4 or claim 5, which includes the step of controlling the nitrogen content of the stout to within the range 25 to 55 mg per litre.

7. A stout brewing process substantially s hereinbefore described with reference to the accompanying drawings.

8. Stout whenever produced by the process as claimed in any preceding claim.