Wednesday, October 15, 2014

Review of Jamie Goode's "Rescuing Minerality": Part II

Jamie Goode gets back onto the "minerality" path after what he terms a "side step" into the concept of terroir. That "side step" was covered in the first installment of our three-part review of Jamie's post titled Rescuing Minerality. This post covers the second major topic in Jamie's post, the contribution of soils to wine quality.

Jamie begins his soils discussion thusly: "The current scientific consensus is that the way that soils have their influence on wine quality is through their effects on water availability... According to this view, soil chemistry is not important." Ronald L. Jackson (Wine Science: Principles and Applications, 3rd Ed.) concurs that any role that soils have on wine quality is indirect. According to Jackson, "Of climatic influences, soil type appears to be the least significant factor affecting grape and wine quality, or to be poorly correlated with wine characteristics." The table below summarizes his understanding of the soil influences in the vineyard.

Soil Influences in the Vineyard
Geologic origin of parent material
Little direct influence on grape quality
Soil texture (size and proportion of mineral content)
Affects aeration, heat retention, water availability, and nutrition availability. In turn affects grapevine growth and fruit maturity
Soil structure
Affects aeration and mineral and water availability
Soil depth
Influences water availability
Soil fauna and flora
·       Generation of the aggregate structure of the soil
·       Interconversions of various forms of nitrogen
·       Extraction (and eventual solubilization) of inorganic nutrients from the mineral content of the soil
Soil color
·       Influenced by moisture content, mineral composition, and organic component
·       Influences the rate of soil warming in the spring and cooling in fall
·       Influences vine growth directly by reflecting photosynthetically active radiation up into the canopy
Soil pH
Affects mineral solubility and availability
Organic content
·       Improves water retention and permeability
·       Enhances soil’s aggregate structure
·       Enhances nutrient availability
Source: Jackson, pp. 240 - 246.
In Jackson's view, one of the most important aspects of soils, as it relates to wine quality, is uniformity as soil variability often results in asynchronous berry development and reduced wine quality.

Jamie feels that the focus on water availability infers that "soil chemistry is not important." But I have not noticed that particular perspective. In the table above, Jackson mentions soil pH and organic content. In my post on soils and vineyard site selection, I excerpted from a table to construct a chart (reproduced below) which shows the characteristics of the best soils; and soil chemistry elements are featured prominently.

Further, the soil's cation exchange capacity (CEC) is a major enabler of the vine's nutrient acquisition. Minerals bind to the clay and humus colloids in the soil and these minerals are released in exchange for hydrogen ions secreted by the vine roots. Cation exchange varies according to soil type. Soil chemistry is extremely important.

Jamie contends that the bulk of soil mineral content comes "from decaying organic material, not decomposed rock and it is microbial activity in the soil that affects the ability of soil to break down organic matter into mineral ions that can be used by the plant." This contention is not shared by Jackson  who stipulates (p. 245) "... the mineral content of soil is primarily derived from the parental rock substrate." The figures below show the weathering of rocks into minerals.


Jackson goes on to say that if conditions are warm and moist, then all organic material is "rapidly mineralized." In cooler, drier conditions, mineralization is only partial (putting the vine's mineral needs at risk if Jamie's position is accurate) and the bulk of non-mineralized material forms the majority of humus.

It would be interesting to get Jamie's perspective on these divergent opinions between him and this Jackson fella.

©Wine -- Mise en abyme

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