GB2059243A

GB2059243A - Process for the fermentation of cocoa beans

Info

Publication number: GB2059243A
Application number: GB7933054A
Authority: GB
Original assignee: Agence National de Valorisation de la Recherche ANVAR
Current assignee: Bpifrance Financement SA
Priority date: 1979-09-24
Filing date: 1979-09-24
Publication date: 1981-04-23
Also published as: GB2059243B; OA06627A

Abstract

A process for the fermentation of cocoa beans, comprises the steps of: fermenting cocoa beans in dispersion in an aqueous medium, with agitation and aeration, with a strain of yeast of relatively high pectinolytic activity, at a temperature of 30 to 40 DEG C, at a pH of 3.4 to 4.1 and for a duration of 20 to 30 hours, followed by fermenting the beans in an aqueous medium, with agitation and aeration, with a strain of acetic bacterium, at a temperature of 40 to 50 DEG C,at a pH of 4 to 5 and for a duration of 36 to 48 hours, the resultant beans being recovered and dried.

Description

SPECIFICATION Process for the fermentation of cocoa beans The present invention relates to a process for the fermentation of cocoa beans.

Hitherto, the technological treatment of fresh beans has, in the majority of cases, been effected by the grower himself. In certain countries (especially Latin America), there are collecting centres which are responsible for this treatment, but the techniques which they use are still very similar to the con ventional method.

Numerous producing nations are searching for an industrial process for treating the fresh beans.

The conventional method of treatment of the fruit of the cacao tree, after picking, comprises three main steps: shelling, which makes it possible to separate the beans from their shell; fermenting the fresh beans; and finally drying the fermented beans.

In most cases, these operations are carried out under very empirical conditions.

(a) Shelling The cacao pod is broken and the beans are extracted by hand.

(b) Fermentation The beans are left to ferment in heaps covered with banana tree leaves, and in baskets or wooden boxes pierced with holes to allow the juices formed during fermentation to flow out.

The purposes of fermentation are: to remove the mucilaginous pulp which surround the fresh bean; to kill the germ of the bean; and to reduce the stringency of the cocoa and develop the precursors of chocolate aroma. Conventional fermentation lasts six days.

The inside of the cacao pod is initially sterile; shelling and extracting the beans by hand causes contamination of the pulp by a wide variety of microorganisms.

A great deal of scientific work carried out on the microflora encountered in the conventional fermentation of cocoa beans and on its evolution has demonstrated the fact that this fermentation takes place under the action of fungi (Aspergillus, Mucor, Penicillium and Rhizopus), yeasts (Saccharomyces cerevisiae, ellipsoides variety, and other species of Saccharomyces, Candida krusei, Kloeckera apiculata, Pichia fermentans, Hausenula anomala and Schizosaccharomyces pombe), homofermentative and heterofermentative lactic bacteria (Betabacterium and Betacoccus), acetic bacteria (Acetabacter rancens, Acetabacter melanogenum and Acetobacter xylinum) and aerobic sporulated bacilla.

(c) Drying The fermented bean contains between 50 and 55% by weight of water. By drying, this proportion is reduced to 7%. In most cases, this operation is carried out in the sun, the fermented beans being spread in a thin layer over drying areas. Artificial driers are also used.

However, the conventional method exhibits numerous disadvantages.

(a) Heterogeneity of the batches The nature of the rise in temperature of the cocoa heap depends on its dimensions. For a small mass, the heat loss is large relative to the amount of heat produced by fermentation.

The biochemical reactions are more rapid at the top of the heap, which is more thoroughly aerated, than at the centre. On the other hand, the temperature at the centre reaches a higher value than at the top.

Mixing is frequently insufficient and gives rise to inadequate aeration of the mass.

(b) Absence ofa rigorous control of the fermentation parameters The conventional method does not make it poss isle to control the inoculation of the fresh beans with micro-organisms.

Furthermore, neitherthetemperature nor the pH of the mass can be influenced during fermentation.

The present invention seeks therefore to obtain homogeneous fermented batches of cocoa beans of uniform quality, to treat industrial amounts of cocoa beans, which are far in excess of the amounts treated by the conventional method, and to shorten considerably the fermentation time, and to do this by: controlling the population ofthe microflora which is involved in the fermentation of the cocoa beans, by restricting this population to one strain of yeast and to one strain of acetic bacterium, acting not simultaneously but successively; rigorously controlling the fermentation parameters, in particular the temperature and the pH, by using water as the fermentation medium, and more thoroughly mixing the product to be fermented, and controlling the oxygenation medium more strictly.

According to the present invention there is provided a process for the fermentation of cocoa beans, comprising the steps of: fermenting cocoa beans in dispersion in an aqueous medium, with agitation and aeration, with a strain of yeast of relatively high pectinolytic activity, at a temperature of 30 to 40"C, at a pH of 3.4 to 4.1 and for a duration of 20 to 30 hours, followed by fermenting the beans in an aqueous medium, with agitation and aeration, with a strain of acetic bacterium, at a temperature of 40 to 50"C, at a pH of 4 to 5 and for a duration of 36 to 48 hours, the resultant beans being recovered and dried.

In the first step, the pectinolytic action of the yeasts causes the disaggregation of the mucilage and an increase in the temperature of the mass of cocoa; the pulp is the site of alcoholic fermentation.

The hydrolysis juices are drained out into the aqueous medium.

In the second step, under conditions of higher temperature and higher pH, the action of the acetic bacteria gives rise to acetic fermentation.

The rise in the temperature of the mass, which temperature reaches 50"C at the end of the operation, and the acetic acid produced cause the destruction of the germinative power of the bean. The walls of the cells constituting the cotyldons become permeable, giving rise to contact between the enzymes and the substrate present in the reserve cells. A series of enzymatic reactions results in: the modification of the various protein fractions; the oxidation of the polyphenols; and the formation of the precursors of chocolate aroma.

Any strain of yeast with a high pectinolytic activity can be used.

The pectinolytic activity can be determined using the method recommended byJ. Brisou in "Techniques d'enzymologie bactérienne" ("Techniques of Bacterial Enzymology"), pages 80-81 (1971), in the case of the pectin methylesterase, and by culture on a pectin-based solid medium in the case of polygalacturonase; in the latter case, the pectinolytic activity results in liquefaction of the medium.The composition of this pectin-containing medium is as follows: Difco malt extract 10 g The pectin unipectin 30 g CaCI2 0.05 g H2O 100 ml The following strains of yeast have proved the most effective: Saccharomyces chevalieri (C B S 400) Candida zeylanoides (described by Langeron and Guerra) Torulopsis candida (described by Lodder) Torulopsis holmii (described by Lodder) Any strain of acetic bacterium capable of converting ethanol into acetic acid can be used. The most valuable strains include Acetobacter rancens and Acetobacter xylinum.

In order to carry out the process according to the invention, a conventional liquid fermenter equipped with a device for agitation and aeration, can be used.

The invention is illustrated, merely by way of example in the accompanying drawing which shows a laboratory liquid fermenter for carrying out a pro cess according to the present invention.

The fermenter comprises a glass, round-bottomed cylindrical reactor 1, having a capacity of 5 litres, a rotary stirrer 2, driven by a motor 3, an air diffuser 4 (with an air inlet and a flow meter 5, a dip tube and a diffuser), a device 6 for regulating the temperature of the medium (the temperature is regulated in a closed loop by means of a proportional regulator acting on an electrical resistor 7, the temperature of the medium being measured by a probe 8), a device 9 for regulating the pH of the medium, (the pH is regulated by means of a proportional regulator acting by the injection of a solution of acid or a solution of base, originating from reservoirs 10 or 11, by means of peristaltic pumps 12, or 13, the pH of the medium being measured bya probe 14), and a device 15 for measuring the proportion of dissolved oxygen in the medium, by means of a probe 16.

A description of the way in which the process according to the present invention may be carried out in the liquid fermenter described above is given below.

Fresh cacao pods (originating from the Ivory Coast) are shelled and the beans are separated from their shells.

Alcoholic fermentation The cocoa beans (2.5 kg) are suspended in water (2.5 litres) in the fermenter and then inoculated with 100 ml of a leaven which has been developed beforehand by the multiplication of a strain of Saccharomyces chevalieri for 48 hours at 27"C, whilst stirring, on a culture medium which has been sterilised beforehand in an autoclave at 105"C for 20 minutes and consists of: bacteriological peptone: 3 9 glucose: 29 (NH4)2HPO4: 1 g H2Oq.s. 200 ml Initially, the temperature of the medium is raised from 25"C to 35"C by heating, the pH is adjusted to 4.12 by the injection of citric acid, and the concentration of the leaven in cells/ml is 1.2.10s.

During fermentation, the temperature and the pH of the medium change in the following manner: temperature: 35"C at the start, reaching 40"C after 16 hours and 45"C after 24 hours.

pH: 4.12 at the start, reaching 3.41 after 16 hours and 3.94 after 24 hours.

the population of yeasts passes through a maximum after 10 hours. The oxygen dissolved in the fermentation medium passes through a minimum when the microbial population is at a maximum.

The yeast fermentation time is 24 hours.

The change in the temperature and in the pH of the medium is given in a Table below: TABLE Fermentation time pH Temperature OC (in hours) Alcoholic fermentation 0 4.12 35 16 3.41 35e40 24 3.94 40e45 Acetic fermentation 40 4.53 45 48 48 4.85 45 50 64 64 4.97 50 Acetic fermentation After this time (24 hours), the beams suspended in water in the fermenter are inoculated with an Acetobacter xylinum inoculum which has previously been developed by culture of a strain of Acetobacter xylinum for48 hours at30 C, whilststirring.

During this acetic fermentation, the temperature and the pH of the medium change in the following manner: temperature: 45"C up to 48 hours, reaching 50"C by the end.

pH: 3.94 up to 40 hours, reaching 4.53 after 40 hours, 4.85 after 48 hours and then 4.97 after 64 hours.

concentration ofthe leaven in cellslml: 4.5.108.

acetic fermentation time: 40 hours The change in the temperature and in the pH of the medium is also given in the Table.

The total duration of both fermentations is 221 days.

After fermentation, the beans are recovered and dried in an oven at 55"C.

Chocolates were prepared from the batch of beans fermented by the process described above, and also from the batch of beans fermented by the conven tional process using a box.

A tasting panel determined their organoliptic qualities. The samples obtained by the above described process according to the present invention were judged to be close to the control manufactured by the conventional method, from the point of view of the aroma and the synthesis mark (organoleptic qualities).

Similar results were obtained on replacing the Acetobacter xylinum by Acetobacter rancens.

Claims

1. A process for the fermentation of cocoa beans, comprises: the steps of: fermenting cocoa beans in dispersion in an aqueous medium, with agitation and aeration, with a strain of yeast of relatively high pectinolytic activity, at a temperature of 30 to 40 C, at a pH of 3.4 to 4.1 and for a duration of 20 to 30 hours, followed by fermenting the beans in an aqueous medium, with agitation and aeration, with a strain of acetic bacterium, at a temperature of 40 to 50"C, at a pH of 4 to 5 and for a duration of 36 to 48 hours, the resultant beans being recovered and dried.

2. A process as claimed in claim 1 in which the strain of yeast is Saccaromyces chevalieri.

3. A process as claimed in claim 1 or 2 in which the strain of acetic bacterium is Acetobacter xylinum or Acetobacter rancens.

4. A process as claimed in any preceding claim in which the temperature in the first-mentioned step is 35"C.

5. A process as claimed in any preceding claim in which the pH in the first-mentioned step is 4.

6. A process as claimed in any preceding claim in which the time of the first-mentioned step is 24 hours.

7. A process as claimed in any preceding claim in which the temperature in the second-mentioned step is 45"C.

8. A process as claimed in any preceding claim in which the pH in the second-mentioned step is 4.5.

9. A process as claimed in any preceding claim in which the time of the second-mentioned step is 40 hours.

10. A process as claimed in any preceding claim in which the fermented beans are dried at 550C.

11. A process as claimed in any preceding claim in which a single strain of yeast is employed in the first-mentioned step.

12. A process as claimed in any preceding claim in which a single strain of acetic acid bacterium is employed in the second-mentioned step.

13. A process as claimed in any preceding claim in which the second-mentioned step is carried out on beans originating from the first-mentioned step, without prior separation of the said beans.

14. A process for the fermentation of cocoa beans substantially as herein described.