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Sunday, February 21, 2016

Soil and Wine - Part 3: Roots Among Rubble

This is the conclusion of my Soil and Wine series of articles. Part 1: Starstuff and Seashells started with the creation of the Earth, how it got its water, how life changed the planet with organic matter, and then covered volcanic soil and limestone. PART 2: Terroir and Texture started with whether or not you could taste the soil in your wine, then explained the different soil types of clay, sand and silt, what they're made of and what they offer.

And now we've reached the end. The final structure of soil type: ROCK/STONE. It's not so much a soil type because you can't grow grapevines on nothing but rocks, but the soil of vineyards can get very rocky and stony.

The Sword in the Stone
What's the difference between rocks and stone? The answer seems to be hotly debated. If you asked me before researching this article I would have answered it this way: Both are very hard, consolidated matter that can be strictly mineral, strictly organic or a combination of both. Rock is jagged as if it was chiseled. Stone is smoother and rounder and weathered. That's what did, and still does, make the most sense to me.

But reading up on the subject almost all night has left me more confused than with answers. One thing I will tell you is to not even bother with the Dictionary definitions. Those are useless. And in the end I couldn't even get a clear, widely accepted definition from geologists. Some say rocks are immovable like cliffs and other formations while stones are smaller fragments of rock. Some say that rocks are minerals regardless of size, whether it's the smallest particle or a boulder, while stone is a formation of organic matter or both organic and mineral matter. Then some say rock is naturally formed while stone is extracted by people for our own purposes. I dunno, dude. It seems like geologists can't even find a straight-forward definition. I like mine.

Regardless of the true definition, if any of the previous soil types also include a good number of rocks or stones then it has the benefit of extra soil drainage and heat retention. Take a bunch of clay and water it down and it just absorbs all that water. Do the same thing but with rocks in the clay and the water will use the sides of rocks and the openings they make to drain better. Let it sit out in the sun and the rocks on the surface will suck in solar heat and blast it back up to the vines, warming them nice and cozily. Also, with more space in the soil being taken up by big clunky things, the less nutrients are in the land. So, in that broad view of soils that I mentioned in the clay section of Part Two, stony and rocky soil is absolutely the best kind for viticulture.


Take a look at the picture of QUARTZ rock. How many times have you seen that rock in your life? Probably millions. I've mentioned quartz a few times in this three-parter and I've been holding off on a definition until now, where I felt it fit best. Quartz is so abundant that the only mineral that there's more of on Earth is also its partner in soil and rock creation: that FELDSPAR none of us have ever frickin heard of. Feldspar is a mineral group defined by the presence of alumina (aluminum oxide) and silica (silicon dioxide). Going into further detail on this one is way over my head.

Of course we've heard of quartz though, at least in passing, because it's used to make jewelry and those funky crystal formations they sell at hippy shops right next to the bongs. Chemically, quartz is a crystal structured, oxide mineral made from silicon and oxygen. Both feldspar and quartz aren't really all that different chemically, being silicates, but quartz comes in several pretty colors: amethyst (purple), citrine (yellow or brown), rose (pink), smoky (grey), and milky (white).

FLINT is a form of crystallized quartz with a mysterious and unresolved past. We all know you can use flint rocks to make sparks and start fires, and that it's the antagonist of gunpowder, but it's also important to the French region of Pouilly Fumé in Loire Valley. Although it lies on Kimmeridge Clay like it's sister Sancerre, Poilly Fumé also has flint. The smokey and flinty character of Pouilly Fumé's Sauvignon Blanc is what separates the two famous Sauvie regions. Even though I do trust that soil composition is not passed along into wine, the presence of something like flint has gotta be the exception. I mean, right? For the lack of a better comparison: grapes over flint could be like malt over peat. All we know is that there's no evidence of flint in Pouilly Fumé's wine but there is benzyl marcaptan, a compound that contributes smokiness and flintiness aromas.

You've already learned that feldspar and quartz as particles are main components of silt and sand. They're also the main components of GRANITE, whose natural habitat is the kitchen countertops of people with money. It's an igneous (from lava or magma) rock formed by crystallized magma under the Earth's surface, with quartz making up 40-60% of it. Granite heats up quickly and retains the heat nicely, giving all the grapes some extra love from the sun. But only certain grapes like Cabernet Sauvignon, Syrah, and Gamay can handle the effectiveness of the drainage without going through some damaging water stress. You'll find granite-heavy soil in Germany's Baden, Portugal's Douro and Dão, France's Moulin-à-Vent in Beaujolais, Brand in Alsace, and Cornas in northern Rhone.

Sauvignon Blanc vine and greywacke rocks
When SANDSTONE (compacted sand) joins up with MUDSTONE (made of clay and silt) to become one form of stone then you've got yourself GREYWACKE. Grey because of its color, and wacke (pronounced wacky) because of the German word for a type sandstone. The first use of the name greywacke was used by German scientist Ernest Dieffenbach around 1840 in order to describe rocks in Germany's Harz Mountains.

New Zealand started using the name in 1903 to refer to the rock that makes up their mountain ranges, which date back to the Carboniferous period (357-299 million years ago), named after all the coal beds that were being created then. During that period amphibians ruled Earth's land but reptiles hadn't spawned off of them yet. Scary anthropods that make your house spiders look like amateurs were also around. There aren't many fossils found in the greywacke but there are some, and they place Waitaki Valley of the South Island as having the oldest greywacke. The mountains have eroded through the history of the islands, so there are greywacke boulders, greywacke alluvial sandstone rocks, and greywacke alluvial soil all over. Even the metamorphic rock (I'll explain soon) in certain spots of the islands are thought to originate from greywacke.

Greywacke isn't just in New Zealand and Germany; there are deposits on every continent except Antarctica (it may even be there too, but I just can't find proof). But New Zealand is pretty much a big island of greywacke and they take pride in it, claiming that it is just one of the factors that make their wines so unique. Don't forget about where New Zealand is and how moist it is down there. There's a lot of marine sand and mud in their soil too. South Africa also has vineyards on greywacke soil, planted mostly with Pinotage.


Weathering shale
"My name is mud." - shale

Among all the sedimentary rocks on our dear planet Earth, SHALE is the most common. Usually grey in color, it's finely grained rock compacted from mud composed of clay minerals and quartz grains. You'll usually find it in lakes or lagoons, or where former ones once were. I've separated it from the other quartz rock, not just because of its clay composition but also because of its physical structure and texture. It breaks down and crumbles back into soil easily, and when it does break down it does so in thin, layered sheets. Being made of mud and clay, its soil is fertile. Also being rock, it retains heat.

Heat and pressure changes chemicals drastically. Just look at what happens to eggs when you cook them. Or when you bake clay into ceramics. Some kinds of rocks, when put under heat and pressure, will change their physical structure and chemical composition through the process of metamorphism. When shale becomes metamorphic rock it's known as SLATE, and Spain has more of it than anywhere else. But slate is at its most important for viticulture along the rivers in Germany, because it heats up so quickly from the sun and releases heat at night in a place that the grapevines need all the help they can get to keep warm. It usually comes in grey, but the red slate of Rheingau and blue slate of Mosel are famous.


Similar to granite in surface and slate in shape, SCHIST is a glossy, crystalline igneous rock. Unlike granite the feldspar and quartz are interwoven with flat molecules, like mica and graphite, that make up most of its composition. So, like slate, when it breaks up it splits up into thin layers. The benefits of schist, besides heat retention and water drainage, is that it's high in magnesium and potassium. GALESTRO is a schist soil in Tuscany, and STEIGE is a schist soil in Andlau, Alsace.


Vineyard with gravel soil
GRAVEL is yet another favorite of Cabernet Sauvignon. Damn grape just can't make up its mind, but it knows that it likes to be forced to dig deep to survive. Rather than have big ol' rocks around like granite, gravelly soil is all about lots and lots of worn pebbles. So many pebbles on the surface and under it that nutrients and water is going to be hard to come by, and those roots even have to fight past the pebbles too. The composition of gravel can be anything that can make those hard pebbles; basalt, limestone, sandstone, etc.

There's all sorts of gravel types for physical structure and location. Bank gravel is next to rivers and streams, bench gravel is where streams used to be higher in a valley, creek rock is from creek beds and river beds, fine gravel has grains smaller than four millimeters, lag gravel is coarse, pay gravel contains gold, pea gravel is the kind you use in aquariums, Piedmont gravel is from mountain streams, gravel-kabobs, gravel creole, gravel gumbo, pineapple gravel, lemon gravel, coconut gravel, pepper gravel, gravel soup, gravel stew, gravel salad, gravel potatoes, gravel burger, gravel sandwich... are you still reading this?

Both Graves on the Left Bank of Bordeaux and Grave del Fruili in northeast Italy are named after the gravelly soil. Sauternes, also on the Left Bank of Bordeaux, and Châteauneuf-du-Pape in Southern Rhone are other famous wine region that rely on it. And now we're heading back to New Zealand to talk about that wacky greywacke again and put this whole research nightmare to rest.

Gimblett Gravels
GIMBLETT GRAVELS is actually a brand owned by a group of winemakers in Hawkes Bay, on the North Island of New Zealand, founded in 2001. They treat the brand as an appellation, and its borders are marked by one thing: the unique soil. In the 1960's the Old Ngaruroro River, which comes down from the greywacke mountains, flooded and left 2,000 acres within Hawkes Bay with alluvial greywacke gravel. The region is drier than the rest of Hawkes Bay, which is a relief in a very wet country. But it's the really hot summers, consistent sunlight hours throughout the year, low altitude, and the benefits of having that gravelly soil that have made it a huge success. Even though Hawkes Bay is the place for growing Cabernet Sauvignon in New Zealand, Syrah has been the real star of Gimblett Gravels.


I know that I took things to a new level of geek with this three-part series, but I learned so much during the late nights I spent researching and writing it. I hope you enjoyed the reading and learned a lot too. As always, if you see anything that should be corrected or added then please contact me. I would hate to be the source of any misinformation.

- Joey Casco CSW/CSS

Part 1: Starstuff and Seashells
Part 2: Terrior and Texture
Part 3: Roots Among Rubble

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1 comment:

  1. Great info. Lucky me I came across your blog by accident (stumbleupon). I've saved it for later!
    Minds Blow



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