This is actually a tough question! What is "hot" very much depends on who you talk to, and a search of the internet produced varied results, no one "expert" agreeing with others. Loosely, there seems to be a trend of going for rare or unusual grape varieties and wines from places one would not immediately associate with grape wine making. There is also a growing trend (maybe obsession is a better word) with "natural wines" on which the jury is still well and truly out. Also, most of these "uber-trendy" wines recommended by "uber-sommeliers" from fancy restaurants tend to be extremely difficult for the average wine enthusiast (me included) to get. So... back to the "3 grape varieties one needs to know about".
Which three amongst many "hot" varieties (they are all "hot" to me when well made)? Well, for starters, I'm leaving out Cab Sauv, Pinot Noir and Shiraz, as these are and always will be the classic "hot" red wine varieties (I can write a book about each of these alone)! And we haven't mentioned "hot" white wine varieties. Here is my take on this...
1. Grenache or Garnacha, its Spanish name where it originated from. This grape variety is well suited to Australia's hot dry climate and long ripening seasons, producing nondescript fruity wines that is high in alcohol but low in acid and tannin. As such, it tends to be blended with other varietals (such as Shiraz) to produce more interesting wines with texture and a modicum of "ageability". Recently, grenache is experiencing a resurgence, especially now with much better understanding how to grow high quality fruit in Australian climate and soils. Well-made Australian grenache can be very delicious, showing raspberry jamminess with a touch of bark spices and luscious mouthfeel when the winemaker manages to extract the right amount of tannins from optimally ripened fruit. Look for single variety grenache from the Barossa Valley and Mclaren Vale.
For those more adventurous and ready to venture beyond Australian wines, I'd recommend you look for "Cote du Rhone" Reds. These are often inexpensive red wines from France's Rhone Valley, where Grenache is often the major component in a blend of up to 13 different grape varieties! In truly great vintages, entry level Cote du Rhone wines (often retailing at big discount chains for $20 or less per bottle) are one of the best bargain Grenache-based wines you can get. 2015 and 2016 are spectacular vintages in the Rhone Valley and should be in stores now! And for a $20 wine, these wines (from great vintages) can age. I've stocked up big on 2010, 2009 and still have a couple of bottles from 2003 which are drinking well.
2. Carmenére - Carmen what? Like the game "Where in the World is Carmen Sandiego" (sorry, I am some sort of a geek after all), this grape variety, originally grown in the Bordeaux region of France, was thought to be extinct, until it was, happily, rediscovered in Chile, where it was mostly mistaken for Merlot grapes. Where in the world indeed! There are fascinating (to a cellar geek) articles on Carmenére which I'll leave for the inner geek in you to trawl the Interwebs for. I am not aware of significant Australian plantings of this varietal, but there are plenty of good, affordable Carmenére from Chile and Argentina. I will never forget my first experience drinking one - smooth, velvety and luscious in texture, dark cherry chocolate liquid blackforest cake!! Like the title character in the game I referred to above, Carmenére is one sexy delicious wine!
3. Chardonnay - okay I "hear" the groans and howls even as I typed the name, but no, I will not apologise for this. To me, Chardonnay is "hot"! It is true that many Australian friends of mine have what amounts to almost a hatred for this varietal, and I don't blame them, given the less than ordinary examples that they endured throughout the 1980s and early 1990s. However, at the turn of the 21st century, most Australian Chardonnay makers started to "get it" and ever since, in my recollection, Australian chardonnay has been improving and evolving for the better, and as a result, this varietal has enjoyed a resurgence.
Good Australian chardonnay do not come cheap, but compared to their illustrious counterpart from Burgundy, much much more affordable. Look to Margaret River, Mornington Peninsula and Yarra Valley, although the best Australian chardonnay in my book comes from Beechworth. If you can afford it, then you might want to start venturing into Burgundy, but here, you really need to do your homework and know not just the top vineyards but also who are widely regarded as the best winemakers for each of those vineyards. But you can get some delicious affordable chardonnays from Mâcon, a sub-region of Burgundy in France, from good wine stores.