GSM is a classic red wine blend from the South of France, namely the Rhône valley. The acronym “GSM” comes from the grape names that make up the primary ingredients: Grenache, Syrah, Mourvèdre. It also indicates the percentages of each wine that makes up the final blend; although exact percentages will vary from year to year (depending on a particular vintage’s quantity and quality of yield), traditionally there will be the highest amount of Grenache, followed by Syrah, and finally Mourvèdre.
But because wine blending (and winemaking in general) is equal parts art and science, vintners will spend days, weeks, maybe even months perfecting their final blend. If you have a chance to participate in this art project/science experiment, do it. It’s an opportunity to learn about the importance of vintage and terroir, harvest and winemaking methods, individual grapes and final blends.