Soil Talk: Sta. Rita Hills with Brandon Sparks-Gillis

Before I started working in the wine biz, you’d never hear me start a conversation with “Tell me about your soil,” but that’s exactly what happened when we had Brandon Sparks-Gillis of Dragonette in our Hollywood tasting bar a little while back. I happened to be knee-deep in Alice Feiring’s the Dirty Guide to Wine, a primer on vineyard soils and bedrocks, and, being a rock neophyte, I had so many questions! 

Brandon, in addition to being a nice human who patiently indulged my questions, was a geologist before becoming a winemaker. To top it off, he is working with one of the most rare soil types in the winemaking world—diatomaceous earth (DE). A white rock comprising mostly silica, it was created over millennia as sea algae deposits on the deep ocean floor were fossilized and then moved onto land by earthquake and volcano activity. Eventually, all this has resulted in the rolling Sta. Rita Hills we see today. You can find smaller deposits of it in Jerez (Sherry) and elsewhere, but Sta. Rita Hills has the largest and purest deposits in the world. 

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What an opportunity to learn more about soils from someone with expertise in both geology and winemaking! He very generously answered my questions, with this caveat: “The topic can get really complex quite quickly, and there's often conflicting info out there, so it should be fun!”


What follows is our conversation—we barely scratched the surface!

KS: Why is geology so complicated to understand from a wine perspective? Does it actually affect flavors? 

BSG: The impact of soil on flavors is very complex, and at this point it is proven more by taste than by scientific evidence. Science has yet to show a direct link between minerals in the soil and minerals in the wine, and thus a lot of scientists claim that "minerality" in wine is a myth, since it cannot be measured.

While that is technically true, we are believers that soil character can influence the flavor (and textural) profile of wines. We can point to the laser-like textural focus and bright acidity of Rita's Crown Chardonnay vs. Chardonnay grown just a short distance away, and to the wild berry and chaparral flavors, energetic acidity, and lean texture of Radian Pinot Noir vs. the generous fruit intensity and round texture of Pinot Noir grown at Bentrock vineyard, a stone’s throw from Radian, as local examples. 

I like to use the wines grown on Kimmeridgian Chain soils in France as an example of minerality and terroir. Most of Chablis and parts of Sancerre (Chavignol in particular) have the same soil type, and flavors and textures can be remarkably similar even through the lens of two different grape varieties in that example. 

KS: So, let’s talk Santa Barbara—how rare is Diatomaceous earth? 

BSG: Extremely rare, both as a material and particularly as a vineyard soil type. As far as I know, Sta. Rita Hills remains the only area where vines are grown directly out of it (there are deposits in Georgia, Tuscany, and Germany, but none that I've found to influence vineyard soils). Radian and Rita's Crown both have significant deposits where we had vines planted right on top of DE.

KS: Is it the same stuff in the White Cliffs of Dover? I thought I read that somewhere. I’m just trying to break it down for us lay people!

BSG: Though it looks like the White Cliffs of Dover or the soils of Champagne, those are both chalk, which is based on calcium, where DE is based on silica, so it's a different minerology. It is similar to chalk in soil structure, but different in the mineral make up. 

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KS: And it’s a sedimentary rock?

BSG: Yes, sedimentary. The vast majority of Santa Barbara County bedrock is marine sedimentary rocks, which were deposited in ocean conditions from about 20–2 million years ago. The DE was deposited in marine conditions (deep ocean water) between 4–6 million years ago, and the main deposits are in what is geologically known as the Sisquoc Formation. 

KS: What’s the difference between "soil" and "rocks/bedrock" in growing grapes?

BSG: Despite a lot of romantic talk in the wine world, vines can't directly pull minerals from bedrock. So soil is incredibly important since it's the substrate that holds the fungal and microbial life that create a "pathway" from mineral to grape vine. Essentially, these microbes make the micro and macro nutrients in the soil available to the vine, they are the conduit of that info. Soil (and sub-soil) can greatly influence vine vigor, yield, and ripening throughout the season; each of those factors can make a significant difference in taste. 

KS: I am reading the Dirty Guide to Wine, and it says that DE absorbs water really well. Does it retain that water? Does it that make it useful in California drought conditions? 

BSG: Yes, it's highly absorbent, which is what makes it commercially useful for things like pool filter applications. Our hunch when we planted was that the absorbance would be ideal for our relatively dry climate. It's important to adapt your viticulture to your local conditions. I know that sounds basic, but one of the most widely repeated "truisms" in vineyards is that they like "well-drained" soils. That's really important in the Medoc where it rains constantly, but in Santa Barbara, we prefer soils which are generally water retaining so we can limit irrigation. What's ideal about DE is that it retains water up until the saturation point, and after satiation then it passes right through; it essentially behaves like a sponge which will suck up water until the saturation point, then let water pass. One challenge we have had is that DE is so good at absorbing water that it will hold water and not release it back to the vine roots. We have worked extensively with high-nitrogen cover crops on the most DE-rich blocks to build soil which can access that water and nutrients. 

KS: So how does that affect the fruit?

BSG: Most of the blocks we are working with feature such a high content of DE that the soils are very thin and under that the vines root in the rock, which is soft enough that vine roots can break it up and keep diving down. What that means is that these sites are very low in vigor resulting in small vines, small clusters, and tiny berries. The small berry size is ideal because the higher skin-to-juice ratio, and typically low yields, create wines with tremendous concentration, depth, and the potential to improve with age. It seems these soils do help preserve natural acid, thus increasing the freshness in the wines, though the cool climate is a major factor in that as well. 

As a footnote to this discussion, it's important to note that things like climate and topography can have an equal (and many times greater) influence on the "flavor" or a wine. In Sta. Rita Hills, the traverse mountain range geography has the most important impact on what we grow where, and on the climate that allows for our uniquely long growing season, so we should cover geography/topography and climate in as much detail as soil if you're game for that. 

KS: YES I AM GAME and that sounds like Part 2!

Terroir geeks: stay tuned!

- Kate Soto