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.
Guts of the Blend

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.

Growth of Australian GSMs

It’s no surprise then that the first Australian GSM came from South Australia, specifically the Barossa Valley. In 1984, James Melton made his first Nine Popes from old bush vines as an act of protest against the government’s vine-pull scheme. The name was a tongue-in-cheek reference to Châteauneuf-du-Pape, where neuf is translated as “nine” instead of “new.” In fact, this iconic wine is a true New World interpretation of a Châteauneuf-du-Pape, made from the three traditional Rhône varieties (Grenache, Shiraz, Mataro), which are grown from “bush” vines. 
Nine Popes hit a sweet spot in the market and soon well-known Barossa producers followed suit. In 1992, Penfolds launched their Old Vines Grenache Shiraz Mourvedre–which has been called Bin 138 Grenache Shiraz Mourvedre from 1998 onwards. One of Torbreck’s first wines, The Steading, produced in 1995, was also a GSM. In fact, David Powell created Torbreck based on his love for Rhône blends and his desire to make wine from some of the oldest and most precious vines in the world. Grant Burge created his Holy Trinity in 1997 and Kilikanoon’s Medley first hit the market in 1999 (under the name the Siblings). As a group, Barossa Valley GSMs typically are rich, generous wines, with a lot of red and black fruit flavors and a distinctive dark chocolate note in the finish. The wines generally age beautifully, but unlike their Rhône counterpart they are often more approachable, even at a young age.
Distinction Down Under

But the GSM trend caught on on the other side of Adelaide as well, closer to the coast in McLaren Vale. The terroir is slightly different there—the wines often have a slight mineral, flinty note. Red and black fruit still dominate the palate, but the finish often has mocha and more earthy cocoa notes.  In general, McLaren Vale wines often retain a little more acidity than their Barossa counterparts thanks to the cooling ocean influence and the higher acidity levels in the Grenache. In 2004, A few winemakers in McLaren Vale created the Cadenzia appellation for their GSMs, with the goal of protecting and re-evaluating old bush Grenache vines, and, very importantly, putting a distinctive McLaren Vale mark on Australian GSM blends.
It’s important to note that not all GSMs in South Australia are made from old bush vines.  Around the $10-$15 mark, there are a lot of easy drinking, fruit-forward GSMs showing off a more juicy, early drinking style of wine. These are often a South Eastern Australian Blend, rather than from a specific terroir. Whilst these wines may lack the complexity and concentration of old bush vine-based GSMs, they are very easy-going and consistent in quality; a great wine to pair with grills and barbeques or to be drunk on their own.

Tasting Notes: Australian GSMs
A big wine, deep purple in color, with a great tannic structure and lifted freshness. It shows some herbaceous characteristics (mint, dried herbs) as well as lots of juicy red and black fruit as well as a little vanilla and coconut from the oak.  The tannins are chewy and the finish a little earthy with cocoa notes. I believe that with age, the wine will develop beautifully and will become almost velvety and richer. It pairs well with game and rich meat dishes such as venison, hare and rib eye steak.
Deep crimson in color, this is a rich, musky wine with dense, almost chalky dry tannins. At the beginning there is a hint of violets, followed by a lot of ripe black fruit (blackberry, cassis and a little black plum) flavors, a few dark chocolate notes and a long savory finish. This wine is very drinkable right now, however I believe the tannin structure will soften and the wine will develop another layer of suppleness in a few years’ time.
Bright red in color with youthful crimson and a seductive blend of dark cherries, cocoa, subtle oak, and earthy notes on the nose. A rich wine, with integrated tannins and layers of red and black berries, sweet spices ( cloves, nutmeg) and a pronounced dark chocolate nose in the persistent finish.
This deep ruby-colored wine has a rich and complex nose of black truffle, pink pepper, sweet licorice and dried herbs . This is a juicy, fresh wine, with flavors of cherry, red plum, cedar and a hint of leather and thyme in the lifted finish. The tannins are ripe and supple and the wine is ready to drink now, though I believe it may gain some complexity with a few years of cellaring.
Brick red in color with crushed red cherries, raspberries and subtle floral note on the nose. A very well balanced wine with a crushed velvet tannin structure, ripe red fruit flavors, a little Turkish delight and a hint of leather and oriental spices (cumin, coriander seed and cardamom) in the long finish. I believe this wine will develop further layers and complexity with age, becoming almost silky smooth and luscious.
Ironstone is a rusty colored laterite granite stone with a high iron content which can be found in vineyards. The higher iron content adds a wonderful mineral freshness to this deep-colored wine. On the nose we have a few violet notes as well as blackberry, raspberry and a little allspice. A complex and layered wine, with fine-grained chalky and mineral tannins and ripe sweet red and black berries which are balanced by provincial herbs.
Yangarra Estate works in a very honest and natural way; they farm organically and let the wines ferment on their indigenous yeasts in open-top fermenters. The wine is aged in French oak barriques. Their 2007 Cadenzia is dark in color, with hints of cherry and roasted beetroot  on the nose. This is a lush and rich wine, showing a lot of black fruit, a hint of boot polish and some dried lavender and roses in the flinty, smoky finish.