GB2338674A

GB2338674A - Tempering of chocolate

Info

Publication number: GB2338674A
Application number: GB9813206A
Authority: GB
Inventors: Judith Graham; Dorothee Pfundt
Original assignee: Societe des Produits Nestle SA; Nestle SA
Current assignee: Societe des Produits Nestle SA; Nestle SA
Priority date: 1998-06-18
Filing date: 1998-06-18
Publication date: 1999-12-29
Also published as: GB9813206D0

Abstract

A process for tempering chocolate which comprises feeding liquid chocolate material into the barrel of a twin-screw extruder, rotating the screws to convey the chocolate through the barrel and through the die and controlling the temperature of the barrel wall so as to enable the chocolate to exit the die at a controlled level of temper. The chocolate is fed to the extruder by means of a pump. The chocolate is fed to the extruder at a preferred temperature of 40 to 55 'C. During passage through the barrel of the extruder, the chocolate is mixed and sheared, cooled and reheated.

Description

TEMPERING OF CHOCOLATE

FIELD OF THE INVENTION

The present invention relates to a process for tempering chocolate.

BACKGROUND OF THE INVENTION

2338674 Plain chocolate is traditionally produced by pressing hot chocolate liquor (usually produced by roasting cocoa beans, cooling, winnowing to form the nibs and grinding the nibs to form the liquor containing from about 50 to 60% cocoa butter) using hydraulic pressure at 350-450 bars to extract the cocoa butter, and mixing sugar, cocoa butter with the chocolate liquor, and conching to produce the chocolate. Milk chocolate is prepared in a similar way but with milk as an additional ingredient and less chocolate liquor. White chocolate contains milk, sugar and cocoa butter without the addition of chocolate liquor.

During the whole manufacturing process, the chocolate has been maintained at temperatures above the melting point of cocoa butter in a paste form. However, cocoa butter exists in a number of polymorphic forms and the nature of the crystalline form depends on the method of cooling the liquid cocoa butter. If the chocolate paste is left to cool naturally, the resulting product will be coarse and grainy due to the development of large fat crystals. The operation of inducing a fine cocoa butter crystallization is called tempering which consists of cooling down the chocolate from about 35'30'C usually to about 25'-26'C for white chocolate, 27-28'C for milk chocolate and about 29'-30'C for plain chocolate with continuous mixing to induce crystallization of the cocoa butter throughout the mass of liquid chocolate in both stable and unstable forms. The temperature is then raised usually to about 28'-29T for white chocolate, 29'-30'C for milk chocolate and about 30'-3 1'C for plain chocolate to melt out the unstable for-in at which stage the chocolate is tempered. On cooling, the total fat phase crystallizes in a more stable polymorphic form and the chocolate paste sets. The tempered chocolate has a glossy appearance, is free from blotches and is easy to demould.

In the conventional tempering machines used industrially, the time taken to temper chocolate is usually about 15 minutes.

2 SUMMARY OF THE INVENTION

We have surprisingly found that by using a twin-screw extruder, the chocolate can be tempered in a shorter time than in conventional tempering machines.

Accordingly, the present invention provides a process for tempering chocolate which comprises feeding liquid chocolate into the barrel of a twin-screw extruder, rotating the screws to convey the chocolate through the barrel and through the die and controlling the temperature of the barrel wall so as to enable the chocolate to exit the die at a controlled level of temper.

DETAILED DESCRIPTION OF THE INVENTION is In this invention, the word "chocolate" is meant to cover plain, white or milk chocolate or chocolate containing cocoa butter equivalents or any fat that requires tempering. Cocoa butter equivalents (CBE) are well known to those skilled in the art (see Chocolate, Cocoa, and Confectionery; Third Edition, 1989, Bernard W. Minifie; AVI), pp 168-172).

The liquid chocolate is preferably fed to the twin-screw extruder at a temperature of from 40' to 55'C. Temperatures higher than 55'C may be used, e.g 60'C or even 80'C or more but such temperatures above 55'C are wasteful of energy and there is no practical advantage in employing such temperatures.

The liquid chocolate may conveniently be fed to the twin-screw extruder by means of a pump. For example, the liquid chocolate may be fed from a container, such as a tank via a flexible, insulated pipe by means of a pump, e.g. a positive displacement pump.

The screws are conveniently low shear screws. The length:diameter ratio of the screws may be from 8 to 36 and preferably from 12 to 20. The screw pitch may increase or decrease downstream or it may be constant.

During passage through the barrel of the extruder, the chocolate is mixed and sheared, cooled and reheated.

3 The wall of the barrel may be cooled by cooled water circulating through a jacket at a temperature, for example of from about 10' to 15'C. The upstream end of the extruder may, if desired, be set at a temperature above the melting point of the chocolate, e.g. from 40' to WC, but this is not usually necessary. The cooling of the upstream end of the barrel wall should be capable of cooling the chocolate to temperatures from about 22' to 30T, preferably from 24' to 29'C while at the downstream end of the barrel wall the temperature should be controlled to enable the chocolate to warm up so that it may exit the die from 25' to 34'C, preferably about 2 7-3 O'C for white chocolate, about 2 P-3 1 'C for milk chocolate and about 29'-32T for plain chocolate.

Extruders may be provided with a plurality of zones extending from the upstream to the downstream end. In such cases, the upstream and downstream zones are set at certain temperatures in order to achieve the necessary cooling and subsequent reheating of the chocolate to obtain the desired level of temper. The cooling and reheating conditions, e.g. temperature and time, may be adjusted by the person skilled in the art to achieve the desired level of temper.

We have found that it is possible to achieve tempering within 1 minute, sometimes within 40 seconds compared with about 15 minutes by conventional methods. In certain cases, it may be desired to have an undertempered or an overtempered chocolate. For instance, in cases where the chocolate exiting the extruder is slightly undertempered, it may be necessary to stir the slightly undertempered 25 chocolate for a period of a few minutes, usually from 2 to 6 minutes, to obtain the desired degree of temper. However, even with the stirring, the tempering time is still three times less than that of conventional methods.

By employing the process of the present invention, it would be apparent to a person skilled in the art how to adjust the degree of temper from undertempered to over-tempered to provide post-tempering handling flexibility Depending on the scale of the extruder, the diameter of the screw may be, for example, from 20 to 20Omm. The screw speed may be, for example, from 1 to 50Orpm. The actual screw diameter and screw speed may be selected by the person skilled in the art according to the requirements. The throughput depends on 4 the screw speed and may be, for instance, from 1 to 5000kg/hr ac.cording to requirements.

The tempered chocolate may be used for making conventional confectionery products by depositing into moulds to form hollow shells or tablets of various shapes, or depositing a coating.

EXAMPLES

The present invention will now be described with reference to the following Examples. Percentages are given by weight.

Example 1

A white chocolate containing approximately 40-45% sugar, 29% milk powder, 5% lactose, 24% cocoa butter, emulsifier and flavours is heated to WC and fed into a Clextral BC21 twin screw extruder by means of a mono pump connected to the extruder via a flexible, insulated pipe.

The details of the extruder are as follows: 9 zones each 10Omm long Screw diameter: 25mm L/d ratio: 900/25= 36 Distance between screw axes: 2 1 mm 25 Screw configuration (low shear conveying elements) from zone 1 to 9: 33, 33, 25, 255 25, 16, 16, 16, 16mm pitch Residence time: 90Omm length (9 zones) & 80 rev/min= >1 min Die: 1Omm diameter, 15mm land Cooling is carried out using a ring main system filled with water and the reheating is carried out electrically. The temperature of the extruder zones is set so that zones 1-4 are at 45'C, zones 5 and 6 are at 2 I'C, zone 7 is at 23'C and zones 8 and 9 are at 28'C.

The chocolate is pumped into the extruder at 45'C at 6.45kg/hr and a screw speed of 40 rpm. It flows through the barrel where the temperature drops to 25'C in zone 5, to 23'C in zone 6, rises to 24'C in zone 7, to 27'C in zone 8, to 2WC in zone 9 and exits the die at 27C. Since cooling only commences at zone 5, tempering is achieved in 5 zones in 70 seconds. The chocolate exiting the extruder is slightly 0 under-tempered but after 5 minutes stirring in a beaker with a palette knife, a good temper is obtained.

The chocolate was deposited into moulds and the shapes demoulded easily and had an attractive glossy appearance.

Example 2

By following essentially the same procedure as in Example 1 using a white chocolate containing 41.5% cocoa butter, but where zones 1-6 are set at 45'C, zone 7 is at 2 YC and zones 8 and 9 are at 3 1 'C, good tempering is achieved in 40 seconds with only 3 extruder zones.

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Claims

1. A process for tempering chocolate which comprises feeding liquid chocolate material into the barrel of a twin-screw extruder, rotating the screws to convey the chocolate through the barrel and through the die and controlling the temperature of the barrel wall so as to enable the chocolate to exit the die at a controlled level of temper.

2. A process according to claim 1 wherein the chocolate is fed to the twin-screw extruder at a temperature of from 40' to 55'C.

A process according to claim 1 wherein the chocolate is fed to the twinscrew extruder by means of a pump.

4. A process according to claim 1 wherein the screws are low shear screws.

5. A process according to claim 1 wherein the length:diarneter ratio of the screws may be from 8 to 36.

6. A process according to claim 1 wherein during passage through the barrel of the extruder, the chocolate is mixed and sheared, cooled and reheated.

7. A process according to claim 1 wherein the cooling of the upstream end of the barrel wall should be capable of cooling the chocolate to temperatures from about 22cl to 30c1C.

8. A process according to claim 1 wherein at the downstream end of the barrel wall the temperature should be controlled to enable the chocolate to warm up so that it exits the die at a temperature from 25' to 34'C.

9. A process according to claim 1 wherein in cases where the chocolate exiting the extruder is slightly undertempered, the slightly undertempered chocolate is stirred for a period of a few minutes to obtain the desired degree of temper.

10. A process according to claim 1 wherein the diameter of the screw is from 20' to 20Omm.

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11. A process according to claim 1 wherein the screw speed is fTom 1 to 50Orpm.

12. A process according to claim 1 wherein the throughput is ftom 1 to 5000kg/hr.

13. A tempered chocolate obtainable by a process according to any of the preceding claims.