Fermentation of fruit juices

Abstract

A method of introducing yeast into a fruit juice such as grape must to be fermented is disclosed. The method comprises feeding dry yeast into a flowing stream of the fruit juice and delivering the flowing stream of fruit juice with the yeast in it to a mixer (10). The fruit juice and yeast emerging from the mixer is fed into a fermentation tank. The yeast can include nutrients selected from inactivated yeasts, yeast autolysates, yeast cell hulls, yeast extracts, amino acids, peptides, proteins, sterols, ergosterol, thiamin, biotin, pantothenic acid, niacin, riboflavin, pyridoxine, minerals and inorganic nitrogen in the form of ammonium salts.

Claims

1. A method of introducing yeast into a fruit juice to be fermented, the method comprising: dispersing dry yeast nutrients in a dry viable yeast to form a dry mixture of nutrients and viable yeast; feeding the dry mixture of nutrients and viable yeast into an uninterrupted flowing stream of fruit juice such that the dry viable yeast comes into direct contact with the fruit juice without a previous rehydration step of the dry viable yeast; delivering the flowing stream of fruit juice with the dry mixture of nutrients and viable yeast in it to a mixer; and feeding the fruit juice and dry mixture of nutrients and viable yeast emerging from the mixer into a fermentation tank.

2. The method as claimed in claim 1, wherein the mixer is a high shear mixer.

3. The method as claimed in claim 1, wherein the dry viable yeast is in powder, vermicelli or pellet form.

4. The method as claimed in claim 1, further comprising: feeding the dry mixture of nutrients and viable yeast from a hopper along a first pipe leading to a pipe junction; feeding the fruit juice along a second pipe leading to the pipe junction; and feeding the mixed dry mixture of nutrients and viable yeast and fruit juice along a pipe which leads away from said junction to an inlet of the mixer.

5. The method as claimed in claim 1, wherein said dry yeast nutrients are selected from inactivated yeasts, yeast autolysates, yeast cell hulls, yeast extracts, amino acids, peptides, proteins, sterols, ergosterol, thiamin, biotin, pantothenic acid, niacin, riboflavin, pyridoxine, minerals and inorganic nitrogen in the form of ammonium salts.

6. The method as claimed in claim 1, further comprising: mixing the dry viable yeast and the dry yeast nutrients into a form of a cream; filtering the cream; and drying a filter cake.

7. The method as claimed in claim 6, wherein the filter cake is extruded to form vermicelli or pellets before the drying step.

8. The method of claim 1, wherein the dry mixture of nutrients and viable yeast comprises dry viable yeasts mixed with one or more dry yeast nutrients selected from inactivated yeasts, yeast autolysates, yeast hulls, yeast extracts, amino acids, peptides, proteins, sterols, ergosterols, thiamin, biotin, pantothenic acid, niacin, riboflavin, pyridoxine, minerals and inorganic nitrogen in the form of ammonium salts.

9. The method of claim 8, wherein the dry yeast nutrients constitute 10% to 70% by weight of the dry mixture of nutrients and viable yeast.

10. The method of claim 8, further comprising inactivated yeast mixed with the dry viable yeast.

11. The method of claim 8, wherein the dry viable yeast constitutes at least 20% by weight of the dry weight of the dry mixture of nutrients and viable yeast.

12. The method of claim 11, wherein the dry viable yeast constitutes more than 60% by weight of the dry weight of the dry mixture of nutrients and viable yeast.

13. The method of claim 8, wherein the dry mixture of nutrients and viable yeast is produced by mixing the dry viable yeast and the dry yeast nutrients in the form of a cream, filtering the cream and thereafter drying a filter cake.

14. A method of producing wine, comprising: dispersing dry yeast nutrients in a dry viable yeast to form a dry mixture of nutrients and viable yeast; feeding the dry mixture of nutrients and viable yeast into an uninterrupted flowing stream of grape must such that the dry viable yeast comes into direct contact with the grape must without a previous rehydration step of the dry viable yeast; delivering the flowing stream of grape must with the dry mixture of nutrients and viable yeast in it to a mixer; and feeding the grape must and dry mixture of nutrients and viable yeast emerging from the mixer into a fermentation tank; and permitting fermentation to proceed in the fermentation tank.

Description

BRIEF DESCRIPTION OF THE DRAWING

(1) For a better understanding of the present invention, and to show how the same may be carried into effect, reference will now be made, by way of example, to the accompanying drawings in which;

(2) FIG. 1 diagrammatically illustrates an installation in accordance with the present invention, and

(3) FIG. 2 illustrates the influence of the present invention on the performance of yeast in fermentation.

DETAILED DESCRIPTION OF THE DRAWING

(4) The installation 10 illustrated in FIG. 1 comprises a high shear mixer 12. A pipe 14 leads from a pipe junction 16 to the inlet 18 of the mixer 12. A feed pipe 22 leads downwards from a hopper 24 and then horizontally to the pipe junction 16. A shut-off valve 26 is provided at the outlet of the hopper. The hopper can contain yeast pellets, yeast powder or yeast in the form of vermicellae. A mixture of yeasts can be provided and there can also be nutrients as will be described hereinafter.

(5) A further pipe 28 leads from a source of fruit juice to the pipe junction 16. The fruit juice can be grape must if wine is to be made or apple or pear juice if cider is being made. A pipe 30 leads from the outlet of the high shear mixer 12 to a fermentation tank (not shown).

(6) A suitable high shear mixer is that available from Silverson under the name Flashmix. A Flashmix mixer comprises a cylindrical stator 32 within which there is a high speed rotor 34. The stator is within an outer casing 36. The rotor is configured to create a suction effect at the inlet 18. When the valve 26 is opened the suction effect draws yeast from the hopper 24 into the chamber bounded by the stator and in which the rotor turns. Centrifugal force drives the yeast and fruit juice outwardly towards the stator and milling takes place in the narrow gap between the stator and the rotor. The stator has perforations in it and the yeast is subjected to high hydraulic shear as it passes through these perforations to the outlet of the Flashmix. The motor which drives the rotor is not shown in the drawing.

(7) For winemakers and the wine industry, the direct addition of yeast into grape must, that is the addition of yeast without a previous rehydration step, using the powder/liquid high shear mixer described above, brings a large number of substantial benefits when compared to the established industry practice (the rehydration process using hot water). These benefits include: Time savings; the addition is almost instantaneous and does not require any follow up; Labour savings: a standard rehydration process may take 2-4 hours in large wineries; Efficiency: the success of the yeast implantation does not depend on worker skills or attention; Simplicity: there is no need to have access to hot water; Flexibility: the same equipment can be used for any type of dry yeast quantities, from a few hundred grams to hundreds of kilograms; The method avoids cross-contamination between strains as the hopper and the rotor/stator mixer are designed for easy cleaning; Water savings: no water is used for rehydration and for cleaning the bucket or other receptacle; Energy savings: energy consumption is smaller than when using hot water; Professionalism: the image of the winery is improved by the use of a modern equipment.

(8) The present invention will now be explained in more detail with reference to the following winemaking examples. For comparison purposes, in all examples, the method of the present invention and a standard rehydration process were used.

EXAMPLES

Example 1

(9) The test was carried out using active dry yeasts in vermicellae (strain Fermicru XL) and pellet (strain Anchor Vin13) forms.

(10) The grape must used had the following characteristics:

(11) Cultivar: Grenache blanc

(12) Sugar: 230 g/L

(13) pH: 3.37

(14) Nitrogen (Free Available Nitrogen): 195 mg/L

(15) Turbidity: 94 NTU

(16) Free SO.sub.2: 10 mg/L

(17) Total SO.sub.2: 45 mg/L

(18) Pasteurized must with 1.7 10E3 wild microorganisms/ml

(19) Temperature: 14 C.

(20) Dry yeast was added at a dosage of 200 mg/l directly into the grape must according to the present invention. Specifically dry yeasts are placed in the hopper 24 and grape must is supplied through the pipe 28.

(21) Dry yeast was added at a dosage of 200 mg/l after the following standard rehydration procedure: heating a solution of glucose at 50 g/l up to 37 C.; addition of dry yeast to this warm solution with continuous stirring; mixing; allowing to stand for 20 min; three successive dilutions with one volume of cold grape must; addition of the rehydrated yeast suspension into the fermentation tank containing the cold grape must.

(22) After addition of yeast according to those two procedures, the fermentation tanks were held at 18 to 20 C. and the relevant parameters were monitored to follow the yeast population and the conditions of fermentation kinetics.

(23) TABLE-US-00001 TABLE 1 Comparison of fermentation parameters and yeast viability during ethanol fermentation of a Grenache grape must inoculated with dry yeast added directly according to the present invention, and according to the standard rehydration procedure. Fermicru XL Anchor Vin 13 Direct Direct addition addition Mode of according according addition of to present Standard to present Standard dry yeast invention rehydration invention rehydration Lag phase (h) 30 24 35 29 Living Yeast 42.4 43 13.4 12.2 at 45 h (10E6 cfu/ml) Residual 21.1 22.8 4.8 8.1 sugars (in g/l) at 550 h

(24) There was no significant difference between the fermentation tank used with yeast added according to the present invention and the tank used with yeast added according to standard rehydration procedure. The figures set out in the tables are consequently not influenced by anything other than the mode of yeast addition.

Example 2

(25) The test was carried out using active dry yeasts in vermicellae (strain Fermicru LS2) and pellet (strain Anchor Vin13) forms.

(26) The grape must used had the following characteristics:

(27) Cultivar: Syrah

(28) Direct pressing

(29) Sugar: 183 g/L

(30) pH: 3.66

(31) Nitrogen (Free Available Nitrogen): 105 mg/L

(32) Turbidity: 30 NTU

(33) Free SO.sub.2: 12 mg/L

(34) Total SO.sub.2: 33 mg/L

(35) Non Pasteurized must with 1.8 10E5 wild microorganisms/ml

(36) Temperature: 16-17 C.

(37) Dry yeast was added, at a dose of 200 mg/l directly into the grape must, according to the present invention. Specifically dry yeasts are placed in the hopper 24 and grape must is supplied through the pipe 28.

(38) A standard rehydration procedure as follows was used: heating a blend of 25% grape must in water up to 37 C.; addition of dry yeast to this warm solution with continuous stirring, mixing; allowing to stand for 20 min; three successive dilutions with one volume of cold grape must; addition of the rehydrated yeast suspension into the fermentation tank containing the cold grape must.

(39) After the addition of yeast at 200 mg/l according to those two procedures, the fermentation tanks were kept at 18 C. and relevant parameters were monitored to follow the yeast population and the conditions of fermentation kinetics.

(40) TABLE-US-00002 TABLE 2 Comparison of fermentation parameters and yeast viability during ethanol fermentation of a Syrah grape must inoculated with dry yeast added directly according to the present invention, or according to standard rehydration procedure. Fermicru LS2 Anchor Vin 13 Direct Direct addition addition Mode of according according addition of to present Standard to present Standard dry yeast invention rehydration invention rehydration % of living 86 86 78 84 yeast 24 h after addition to grape must Implantation 80 80 90 100 control: % of selected yeast strain among total yeast population Time to 9 9 9 8 complete fermentation (days) Residual 0.44 0.17 0.02 0.02 sugars (g/l) at 240 h

(41) There was no significant difference between the fermentation tank used to add yeast according to the present invention and the tank used to add yeast according to the standard rehydration procedure. The figures set out above were consequently not influenced by anything other than the mode of yeast addition.

(42) The different Syrah wines obtained were analysed at the end of fermentation.

(43) TABLE-US-00003 TABLE 3 Composition of ros wines obtained after complete ethanol fermentation of a Syrah must inoculated with dry yeast added directly according to the present invention, and according to standard rehydration procedure. Fermicru LS2 Anchor Vin 13 Direct Direct addition addition Mode of according according addition of to present Standard to present Standard dry yeast invention rehydration invention rehydration Ethanol 11.65 11.6 11.6 11.55 content (%) Total acidity 3.9 4.05 3.75 3.85 (in g/l sulfuric acid) Volatile 0.11 0.15 <0.06 <0.06 acidity (in g/l acetic acid) Isoamyl 8.64 7.08 7.56 6.63 acetate (mg/l) hexyl acetate 0.76 0.63 0.65 0.61 (mg/l) ethyl 1.79 1.53 1.51 1.44 hexanoate (mg/l) ethyl 1.31 1.07 1.40 1.28 octanoate (mg/l)

(44) The completion of ethanol fermentation in all tanks was reflected in similar ethanol content in all wines.

(45) Surprisingly, the wines obtained using the winemaking process including the introduction of dry yeast in accordance with the present invention have been found to be of higher quality than control wines made from the same grape must but after addition of rehydrated yeasts. This increased quality was noticeable as the wines obtained had a higher ester content (more aroma) and a lower acetic acid content (lower volatile acidity).

Example 3

(46) A test was carried out using two different active dry yeasts preparations of the same strain (commercial yeast Fermicru AR2) in vermicellae forms. Standard commercial yeast Fermicru AR2, produced according to standard yeast manufacturing practices. A Yeast Product AR2 produced as described below: Strain AR2 is grown as fresh cream yeast, according to standard yeast manufacturing practices The cream yeast is blended with dry inactivated yeast in a ratio of viable yeast/inactivated yeast 70/30 (dry weight basis) The blend obtained is then vacuum filtered, extruded and dried according to standard yeast manufacturing practice. This Yeast Product AR2 contains 70% viable dry yeasts on a dry weight basis

(47) The characteristics of both yeasts used for Example 3 are listed in Table 4

(48) TABLE-US-00004 TABLE 4 Characteristics of standard commercial Fermicru AR2 and Yeast Product AR2 commercial Fermicru Yeast Product AR2 AR2 Total viable yeast count 4.00E+10 2.49E+10 (CFU/g) Active yeast >99 70 (% dry matter) Inactive yeast <1 30 (% dry matter) Dry matter % 94.00 92.24

(49) The grape must used had the following characteristics:

(50) Cultivar: Chardonnay

(51) Sugar: 210 g/L

(52) pH: 3.66

(53) Nitrogen (Free Available Nitrogen): 177 mg/L

(54) Turbidity: 40 NTU

(55) Free SO.sub.2: 5 mg/L

(56) Total SO.sub.2: 18 mg/L

(57) Temperature: 19.5 C.

(58) The standard commercial yeast Fermicru AR2 was added at a dosage of 200 mg per liter of grape must directly into the grape must according to the present invention. Specifically dry yeasts are placed in the hopper 24 and grape must is supplied through the pipe 28.

(59) The Yeast product AR2 was added at a dosage of 300 mg per liter of grape must directly into the grape must according to the present invention. Specifically dry yeasts are placed in the hopper 24 and grape must is supplied through the pipe 28. As this yeast product contains 70% of viable yeasts, the total population added per litre of must was similar to Fermicru AR2.

(60) After direct addition of both yeasts to the Chardonnay must according to the method of present invention, both fermentation tanks were held at 18 C. and the relevant parameters were monitored during the initial 80 hours of fermentation, to follow the yeast population and the conditions of fermentation kinetics. The fermentation kinetic curves, expressed as the instant production of CO2 (dCO2/dt, expressed in g/l/h) as a function of time, clearly show (FIG. 2) a better start of the fermentation with the Yeast Product AR2 than with the commercial yeast Fermicru AR2.

(61) In FIG. 2 the line designated 1 shows the rate of carbon dioxide release with time when the commercial yeast Fermicru AR2 is fed into the grape must in accordance with the method of the present invention. Line 2 shows the rate of carbon dioxide production with time when the Yeast Product AR2 is fed into the grape must in accordance with the method of the present invention.

(62) This faster start of fermentation is also reflected in other fermentation and yeast viability parameters, as shown in Table 5. The total yeast population per ml of fermenting must was very significantly larger when the Yeast Product AR2 was used than the commercial yeast Fermicru AR2.

(63) TABLE-US-00005 TABLE 5 Comparison of fermentation parameters and yeast viability during ethanol fermentation of a Chardonnay grape must inoculated with a commercial yeast (Fermicru AR2) or with an experimental Yeast product (AR2) added directly to the must according to the present invention. Commercial yeast Fermicru Yeast Product AR2 AR2 Lag phase (hours) 28 24 % of living yeast 24 h after direct 57 63 addition to grape must Total yeast population at 18 9.2 14 hours (in CFU/ml) Total yeast population at 50 42 56 hours (in CFU/ml) Total yeast population at 74 65.2 74 hours (in CFU/ml) Residual sugars (g/l) at 80 h 61.4 55.1