The science behind your favourite alcoholic beverage

Alcoholic beverages such as your favourite wine need to go through a lot of scientific tests before they get to the point where they can be enjoyed. Before alcohol can be sold, it has to go through rigorous tests to make sure what is inside the bottle is indeed what it is being sold as.

One of the tests that is used, is to look at the carbon isotopic composition of the product. Different types of alcoholic beverages, such as wine, whisky and cider, have very specific carbon isotope ranges which are tested to ensure the product has not got other ingredients added to it. The adding of ingredients such as cane spirits to wine is known as adulteration. The University of Pretoria’s Stable Isotope Laboratory is the only lab in the country that does regular testing of alcohol products to make sure that they comply to the regulations for the production of alcoholic beverages. The lab works very closely with the Department of Agriculture, Forestry and Fisheries (DAFF)’s Directorate: Food Safety & Quality Assurance to ensure that South Africa’s alcoholic products meet the strict international standards and regulations for these products.  

Head of the lab, Dr Grant Hall does all the testing in the lab himself, using a stable light isotope-ratio mass spectrometer to measure the relative isotope or isotopes in a given sample. In the case of alcohol, carbon isotopes are measured and depending on the range the sample falls into, determines the plant origin of the sample. Isotopes (such as carbon or nitrogen) are forms of the same element that differ in atomic mass. All alcohol types, whether ciders, spirits or wines, have a particular carbon isotopic range.

Products made mostly from grapes, such as wine, have a range of carbon isotope ratios that fall in the C3 plant category. Grapevines follow a particular photosynthetic pathway taking carbon from the atmosphere and processing it in the plant to form tissues such as fruit. Spirits, such as cane spirits, are derived from sugar cane (a grass species) which is a C4 plant. C3 and C4 plants each follow a slightly different metabolic process, producing different carbon isotope ratios. Therefore, wines will have a different carbon isotopic range to ciders or spirits for example.

Dr Hall receives samples of a range of products from DAFF, as well as from various manufacturers. He tests the product’s carbon isotope range to determine whether the product has been adulterated. Sometimes, additional products such as cane spirits or cane sugar are added to wine to raise the alcoholic percentage or to bulk up the volume of the drink. There are regulations as to the amounts of additional products that may be added. If these regulations are not followed in such a case, it would be illegal to name the product a wine.

With the increasing popularity of cider drinks, there is an increase of local producers of ciders, as well as drinks being imported from Europe. Stringent local and international regulations specify that the drink has to comprise a minimum of 80% of apple or pear to qualify as a cider.

Typically, Dr Hall will run each sample through the mass spectrometer three times to determine the product’s carbon isotope range. If a product does not fall into the range it is marketing itself as, Dr Hall will send an explanatory report to the Department or manufacturer. If it falls out of the range, the product would need to amend its recipe.

Dr Hall remains completely impartial in his work. All samples receive a lab number rather than being identified by its product name. This ensures that there is no bias in his findings and because products are only handled by him, there is no tampering with products. This is particularly important, should any products ever be taken to court.

Food forensics is a thriving industry overseas and labs in the USA and Europe have made some major advancements in the field. The testing of food items such as meat, cheese, honey and alcoholic beverages, has become a regular occurrence due to the large amount of money involved in these markets. Through the analysis of samples, these isotope labs are even able to determine the geographic location the sample comes from - a process known as source tracing. Other forensic isotope labs have even extended their analysis to things like drugs and explosives and are able to trace where theyse items originate using isotopic analysis.

While the UP lab is currently the only lab that does these alcohol tests, there is great potential for growth in the field. Dr Hall says it would be ideal if there could be more labs in South Africa that are commercially available and accredited, in order to expand the market. Other isotope research colleagues are developing isoscapes which are isotopic maps of areas. These isoscapes will include the creation of a database of oxygen and hydrogen isotope ratios from both ground and rain water from across South Africa. Conducting further tests on samples and using the water isotope database, scientists like Dr Hall can extract water from, for instance a sample of wine, and from the isotopic ratios of the extracted water information determine the geographic location where the wine was produced.

UP’s Stable Isotope Lab is also used by postgraduate students conducting a range of other research in a variety of disciplines. The lab provides work space and training for students, to allow them to prepare their samples for isotope analysis. Currently some of the other studies taking place in the lab include fertiliser tests for plant crops, dietary choices of otters, and a range of research work from the Mammal Research Institute’s team based on Marion Island, as well as on-going baobab research which spans across southern Africa.

Alcohol samples ready to be analysed (Photo by Dr Stephan Woodborne)