Down Under, the traditional Southern Rhône blend of grenache, syrah, and mourvedre is commonly known by the name GSM (or SGM) — based on the Australian no-nonsense attitude and strong belief in "calling a spade a spade," or calling these Rhône blends after the varietals they’re made of. In further Australian style, abbreviations GSM and SGM were adopted based on the order of the letters (stipulating which varieties are most dominant in the blend). The only difference in naming: in Australia, syrah is commonly known as shiraz, and mourvedre goes by the name of mataro.
Even if there is no exact blending recipe, grenache and shiraz generally make up the bulk of the blend. Grenache is a vigorous and generous vine, producing a light colored juice with flavors of red berries and a hint of sweet spice (clove, cardamom, allspice). It brings warmth and fruitiness to the blend as well as alcohol. Shiraz is more full-bodied and fleshy, and generally contributes more black fruit flavors as well as leather, bitter chocolate, and peppery notes. It also adds color, structure, tannins, and balance to the blend. Mataro is responsible for flavors of ripe red fruit (plums, cherry), cigar smoke, and dried meat, but also adds elegance, freshness, and structure.
Australian GSMs often have minty or eucalyptus notes in the nose, and a hint of dark chocolate in the finish. Grenache, shiraz, and mataro have a long history in Australia — they were among the first vitis vinifera James Busby brought back from his trip to France and Spain in 1831. In 1839, the three varieties were brought to Southern Australia, where they flourished. They were originally used for the production of fortified wine (the backbone of the Australian wine industry till the 1960s). Some of the oldest vines of grenache, shiraz, and mataro can still be found in South Australia, where some vines are more than 150 years old.
However, as a direct result of the decline of the fortified wine industry, a lot of old grenache and mataro vines were ripped up and replaced with cabernet sauvignon in the vine-pull schemes of the '80s. In recent years, planting have increased slightly, but both grape varieties are but a shadow of their former self and are today almost exclusively found in South Australia. Heathcote (Victoria) and Margaret River are the two main exceptions to this rule.
— Caroline Henry, Snooth