“Sorry, this wine tastes like 3-MPD”

Glycerine, or glycerol, is one of the most important and abundant molecules in wine. From a chemical point of view, it is a polyol (polyalcohol) that in its pure state is a syrup-like uncolored liquid characterized by a pseudo-sweety taste. Its origin in wine directly arises from yeasts’ action during glycerol-pyruvic fermentation. In fact, it is the first molecule, as for abundance, among alcoholic fermentation by-products, reaching concentrations between 3 and 10 g/l according to the grape variety, the kind of yeast, the initial amount of sugars, and the fermentation temperature. Its exact concentration is easily detectable by the same analytical method used for the detection of sugars by HPLC-RID (liquid chromatography with refraction index detector).

Unlike other fermentation by-products, such as acetic acid, glycerol in high concentration provides qualities to wine, giving it softness, roundness, and sweetness that counteract the hardness and sharpness brought by polyphenol components.

Glycerol can be industrially produced through many synthetic pathways. The most common pathways involve the transesterification process of animal and vegetal oils and fats or distillations and reactions of petrochemical product. Synthetic glycerine has several uses in cosmetics, pharmaceutical, and food sectors and the paints and similar products industry.

The addition of technical glycerine in wine to enhance its organoleptic qualities is forbidden since it represents an adulteration of the final product. The detection of this kind of counterfeiting is possible with the detection of some specific markers: cyclic diglycerines and 3-methoxypropan-1,2-diol (3-MPD). In fact, these molecules are not generated by natural fermentation caused by yeasts in wine and are present as impurities in technical glycerine. Consequently, if they are present in wine, they confirm that glycerol in the product is of exogenous origin. Cyclic diglycerines are formed by two glycerine molecules bound to each other. They are six compounds deriving from the production of a technical preparation from petrochemical products, while 3-MPD derives from triglycerides (fats) transesterification by methanol.

As required by OIV-MA-AS315-15 R2007 official method, the analysis is performed in isotopic dilution by extracting interest molecules from a wine matrix with organic solvents and analyzing the extract by gas-chromatography with mass spectrometry detector (GC-MS). The application of this technique, far more sensitive than the one used to detect glycerol, is required since these molecules are very low in abundance in technical glycerine and so their concentration in wine is very low.

In view of the ever-increasing demand for this detection, both by Italian and foreign control bodies, the Centro Analisi CAIM laboratory set the analytical method, to give fast and complete feedback to concerned companies. The laboratory plans method accreditation according to EN ISO/IEC 17025 Standard by the end of 2023.

FUN FACT

The formation of arcs of wine residue on the glass surface during rotation is often connected to glycerol in wine. This is not correct since arcs directly depend on the alcoholic title of the product. In fact, alcohol is more volatile than water and other components in wine and tends to climb glass walls more rapidly, so creating characteristic arcs.