SOILS

Soils and wine – a mysterious relationship!

A good example of the difference soil and climate makes to wine flavour can be found with Riesling grown in the Mosel region in Germany, which tastes very different from Riesling grown in the Clare Valley. The topography of the landscape, the climate, the soils, the vineyard management, local cultures and traditions all have the ability to influence how foods and wines from different places taste. But as we refine our search to identify the most important factors responsible for these differences, we run early on into the problem of trying to understand and quantify the relative importance of soil.

This is made even more interesting by the traditional promotion of soil as the basis of vineyard terroir by the French and the appeal of the notion to wine consumers. It’s tempting to associate the stony/mineral flavours of Mosel Riesling with the slate soils the vines grow in. Or the pithy dryness of Chablis with the chalk-rich soil in which it grows. But we cannot explain this relationship yet in scientific terms. We can demonstrate an indirect effect via soil physical differences influencing moisture retention which impacts on vine growth but no direct flavour effect. There is no known mechanism for how soil can directly influence wine flavour but we feel it does. So it remains a mystery for the moment…

So soil and wine flavour…is there really a link? And what about the impact of rootstocks?

McLaren Vale has an exciting project underway to determine districts within the region based on flavour and early indications suggest that soil/geology has a role to play.

We have several advantages in conducting this research.

– One is the diversity of soils/geologies we have within our small region, minimising the effect that other influences such as climate play.

– Another is the absence of phylloxera (an insect which kills grapevines by attacking their roots, now spread to most wine regions of the world) which allows us to grow our vines here on their own roots, giving the most direct connection possible with the vineyard soil/geology.

This could be more important than is generally recognised, perhaps allowing our vines to more readily reflect their terroir and produce wines with a ‘sense of place’, without the confounding effect of rootstocks. Australian wines (generally) have been described as bright in fruit character or ‘bottled sunshine’.

Perhaps the absence of rootstocks impacts on the clarity and purity of wines produced here? There is much about the influence of rootstocks which is not known but our feeling is that if you really wish to see the influence of soil on wine then rootstocks are a confounding factor which is best avoided. For clarity of site expression, you can’t beat the root system that nature provided.

This is not discussed in recent books about the subject, even from authors who are passionate about exploring the soil/wine relationship. Perhaps they have never considered the potential impact of rootstocks or more likely it’s simply not worth discussing because the presence of phylloxera in France, Europe and most of the world necessitates the use of them nearly everywhere except Australia. We don’t realise how lucky we are.

Soil 3 – Langhorne Creek Loam

The alluvial soils of the Langhorne Creek Shiraz and Cabernet blocks. Here on the flood plain of Langhorne Creek, elevation differences of less than 1 metre can make a big difference. Our blocks are low enough to receive a winter flood but high enough and with sufficient clay content to avoid excess vigour, which can trouble the low lying areas. It’s a fine line. The right combination results in big vines growing in perfect balance, producing deep, full flavoured wines.

Soil 2 – Throughout BJ’S block, McLaren Vale

The soil in BJ’s block has a lighter brown colour to it. It’s a sandy loam topsoil which contains small pieces of white quartz, over a clay subsoil which provides moisture retention. The gentle slope ensures good drainage. This block faces the Gulf of St Vincent and is quite exposed to the sun and wind. The wines are somewhat brighter and more refined than the Winery Block produces. Grapes grown on both blocks make Eclipse.

Soil 1 – Typical of the Winery Block, McLaren Vale

Sandy loam (0-25cm) over heavy orange clay is found on 80%+ of the Winery Block. The clay is perfect for providing the vine roots with the moisture they need to get through our long, hot summers. The vines growing on this soil are long lived and of modest vigour and yield.

The wines produced from the clay soil are dense and concentrated. Interestingly, there is a gravel fan at the top of this block where the vines grow quite differently. This patch of soil is not as cold and the vines do not sleep as deeply in winter, being the first to break bud in the spring. They are consequently showing their age more than the rest. The wines from the gravel soil are also softer and earlier maturing.