Charcoal: What are we barbecuing with?

Grilling with charcoal is the trend. According to figures from the German Federal Statistical Office, consumption in Germany in 2016 was 250,000 tonnes – and rising. Most of the wood used does not come from "domestic forests". Around 85 % of the sold charcoal is imported from abroad, often from tropical and subtropical regions, but also from Eastern European forests.

New microscopy method

Since 2016, several consumer and environmental protection organisations have asked the Competence Centre to test charcoal batches that are commercially available in supermarkets, petrol stations or DIY stores.

For the determination of the selected charcoal/briquette samples, a special 3D reflected light microscopy technique (Video) was used to display the characteristic anatomical structural features. In contrast to the microscopic determination of solid woods, charcoal cannot be prepared as flat (planar) cut samples, as the structure is strongly decomposed by the charring process and is very brittle. With the help of the new digital microscopy technique, the uneven areas within a programmable field are digitally scanned and assembled. This produces a three-dimensional image, which is converted into a two-dimensional representation (Fig. 1).

The quality and sharpness of the images correspond to the results obtained in the "classical" way, i.e. when preparing microscopic thin sections. The high-resolution imaging enables the detection of very small cell structures and comparison with the structural characteristics of more than 400 commercial tree species in the databases of the Thünen Institute (Figs. 2 and 3). With the help of an integrated polarisation technique, through which the images appear optically green, the contrasts of the structural features can be enhanced and native woods can be distinguished from tropical and subtropical species.

High proportion of "critical" assortments

In 2016, the Thünen Centre of Competence investigated 18 charcoal assortments from Austria. Three charcoal sacks contained admixtures of tropical woods. For another three sacks, the declarations did not match the identified woods.

Another study (20 assortments), carried out in 2017 on behalf of the WWF, revealed:

• Approximately 50 % of the assortments traded in Germany did not contain any information on the woods or tree species used,
• only 30 % of the charcoal and briquettes came from certified sources (FSC or PEFC),
• About 40 % of the assortments traded in Germany mainly contained wood from subtropical or tropical regions. Three-quarters of these consisted exclusively of tropical/subtropical woods, while in one-quarter these woods were added to woods from temperate latitudes.

Further comprehensive test orders have followed to this day. The investigantions of about 450 assortments and about 6,750 microscopically analysed individual samples have provided basic knowledge about the used woods and deviations from the declarations.

In detail, it could be stated in 2019 that about 20 % of the investigated assortments had to be assessed as "critical" with regard to the declared woods/tree species:

• Assortments which advertise the use of exclusively certain wood species ("beech wood") and in which admixtures of other "domestic woods" could be detected.
• Assortments that do not contain information on the woods used: These batches usually consist entirely of tropical/subtropical woods.
• Assortments with the declaration "from domestic hardwoods": In addition to domestic woods such as beech, maple or oak, it was also possible to detect admixtures of tropical/subtropical woods. In two cases, the batches were even FSC or PEFC certified.

In 2020, the Thünen Institute in cooperation with the WWF has carried out further investigations in a Europe-wide approach. For this purpose, 150 charcoal assortments from 11 European countries were analysed. The results are summarised in the WWF brochure "Grillkohle 2020 - Eine EU-Marktanalyse".