Water Determination in Chocolate and Cocoa using Karl Fischer Titration

Cocoa and chocolate have a fascinating history. Pre-Columbian cultures in Latin America cultivated cacao trees over 3,000 years ago. The main use was a chocolate beverage called xocolatl. In Mayan and Aztec cultures the cacao beans were not only used for xocolatl, but also as a very valuable currency. In the early 16th century, Spanish conquerors brought the first cacao beans back in their ships, and chocolate began to conquer Europe.

The largest consumers of chocolate today are the western world countries, while the largest cacao-producing countries are Ivory Coast, Ghana, and Indonesia. Nearly 75% of the world’s cocoa crop comes from Africa.¹ Figure 1 shows the chocolate confectionery consumption per country in kg per head (2007).

Figure 1 Ranking of consumption: chocolate confectionery 2007²

The tropical cacao tree, Theobroma cacao, probably originated in the northern part of South America, where it grows in a warm, moist climate. As an evergreen, it flowers all year round, and it yields 20 to 50 ripe fruits per tree. The cacao beans are the seeds of these fruits.³

After the ripe cacao pods have been harvested, the cacao beans are removed from the pods and left to ferment for five to seven days. The fermentation process naturally removes all remaining fruit pulp from the beans, while the beans change their color and develop many aroma compounds. After fermentation, the beans are dried to stop the fermentation process and reduce the moisture content for storage.

The further processing steps leading to cocoa powder and chocolate are described in Figure 2. The beans’ water content is a very important factor and should be 6 to 8%. If the water content is too high, microorganisms can infest the beans and their quality will suffer. After the beans have been roasted, the water content is further decreased to approximately 3%.

Figure 2 Production of chocolate and cocoa powder³

Regulations

Water content is also an important parameter for chocolate and chocolate products and must be closely monitored. The Swiss Food Register states in Method 1010.1 Determination of Water content of Cocoa and Cocoa Products, acc. to Karl Fischer, that a homogenous sample, if necessary finely grated or melted for two hours at 40 ± 2 °C, can be titrated in a 1:1-mixture of methanol and chloroform as a Karl Fischer working medium. Also AOAC International^® gives an official method for moisture in cacao products, using Karl Fischer.⁴ Our HYDRANAL^® laboratory has developed applications for chocolate and chocolate products, using volumetric KF titration techniques, which are described below.

Application: Water Determination in Chocolate

Chocolate and milk chocolate samples with high fat content need pretreatment before the water determination can be carried out. Directly before the titration, the chocolate sample should be ground or grated. It should not be left exposed to ambient air once it is grated, otherwise its water content will change according to the room conditions. In order to dissolve the fat and finely disperse chocolate samples in the Karl Fischer working medium, the addition of chloroform to the working medium is recommended. Alternatively, the titration can be carried out at 50 °C. Recommended sample size is approximately 1 g. Before starting the titration and after sample addition, a stirring time of two to three minutes should be applied. Titration duration is about three minutes, following these procedures:

(Application reports L071 Chocolate, and L079 Milk chocolate)

Application: Water Determination in Chocolate Truffles and Pralines

Chocolate truffles and pralines are usually composed of different layers, which also have different water content. It is therefore crucial to create a homogenous mass and take a representative sample. For example, a single praline can be quickly homogenized, using a mortar; afterwards, the sample should be stored in a tightly sealed container. Larger sample amounts can also be homogenized, using a blender.

(Application report L028 Chocolate truffles and pralines)

When methanol is used as the sole component of the working medium, the chocolate mass disperses very slowly. The addition of formamide for dissolving contained sugars, as well as chloroform for fat content, is highly recommended. Carrying out the titration at an elevated temperature of 50 °C also has a positive effect on the dissolving of the chocolate samples. The duration of the titration may vary approximately from 3 to 6 minutes, depending on the composition of the sample. In this application, a sample size of approximately 400 mg was used.

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Materials

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