Quantitative determination of 2-methoxy-3-isobutylpyrazine in red wines and grapes of Bordeaux using a stable isotope dilution assay

Quantitative analysis of 2-methoxy-3-isobutylpyrazine (MIBP) in grapes and wines was developed, using a stable isotope dilution assay. This was applie d to red grapes and wines from the Bordeaux region. The grapes and the wine s of the 1995 and 1996 vintages came from the three most frequently used va rieties of the region, Merlot, Cabernet Franc and Cabernet Sauvignon. The w ines made from Cabernet Sauvignon grapes exhibited levels of MIBP (mean con centration, 12 ng l(-1) for 1996 vintage and 13 ng l(-1) for 1995 vintage) close to or higher than its odour threshold in wines (10 ng l(-1)) and slig htly higher than the amounts found in the Merlot wines (mean concentration, 8 ng l(-1) for 1996 vintage and 4 ng l(-1) for 1995 vintage), especially t hose of the 1996 vintage. The variation in the levels of MIBP in grape samp les and in their corresponding wines was monitored at four different stages towards the end of maturation. MIBP was present in all grapes and wines an alysed, even in surmaturation. A linear trend was observed between grapes a nd wines of the three cultivars during maturation. (C) 1999 Elsevier Scienc e B.V. All rights reserved.