Andrew Jefford reviews professor Alex Maltman’s recently published book, Vineyards, Rocks, & Soils.

There are wine books, and there are essential wine books.  The former sit in a bookcase to the right of my desk, but the latter fill two small shelves within grabbing distance to the left.

Essential wine books need not be exquisitely written nor sumptuously illustrated; they tend not to contain a single tasting note.  They become, though, worn, scuffed and annotated by dint of usage.  These are the key sources of factual reference through which wine’s complexity can be explored and understood.

I’ve just added a new volume to the shelves on the left.  It’s called Vineyards, Rocks, & Soils: The Wine Lover’s Guide to Geology by Professor Alex Maltman (Oxford University Press).  I have contributed a small (unpaid) Foreword to this book, but it is Maltman’s lucid, dense and deeply informative text which merits its inclusion in the dog-eared pantheon.

No student of wine should be without this book; every wine writer and sommelier should read it, several times.  Supposing that we all do this, the language and discourse of wine will move forward, and the common understanding of the ways in which vines interact with soils and rocks will change from folkloric to something which is sustainably scientific.  The book is an essential contribution to the as-yet-inexistent academic discipline of ‘Terroir Studies’.

Readers may be familiar with James Wilson’s book Terroir (a descriptive geology of France’s vineyard regions) and Great Wine Terroirs of Jacques Fanet (a non-exhaustive look at the geology of global wine regions), as well as Robert E.White’s Understanding Vineyard Soils (a technical work for viticulturalists).  Maltman’s book is much broader in scope than these, as well as more useful in practical terms for wine drinkers.  Wilson’s and Fanet’s books are liable to be misconstrued without careful reading of Maltman’s work.

His aim is to help those who enjoy wine understand something of the diversity of rocks types found in vineyard regions, and learn how the soils which lie on top of them are formed.  He explains, too, how rocks move, both at a vast tectonic scale as well as via folding, flowing and faulting; and he gives readers an account of weathering, of topography and of landscape formation.  Most geologists litter their writing with jargon and technical terms, and the result is usually opaque and incomprehensible for the lay reader.  After a lifetime of teaching undergraduates, Maltman writes with clarity and limpidity.  His breadth of culture is palpable in his literary references and evident interest in etymology.  Nothing in this book is opaque; much is entertaining.

In the middle section, there are necessary chapters on the three families of rocks (igneous, metamorphic and sedimentary), seasoned with notes as to where you may find such rock types in wine regions.  They will help you use the terminology accurately and thus avoid confusing tuff with tufa, and encourage you to relax about the differences between slate and schist.  You’ll grasp the vital difference between the physical characteristics of a rock and its chemical or mineral composition (and so realise that there can be many different types of slate, schist or limestone, meaning that use of these terms alone is rarely descriptively adequate).

To my mind, the most useful chapters of the book come at the beginning and the end, however.  I’ll take the two parts separately.

Vine roots never explore ‘limestone’ or ‘schist’: those are our classificatory labels of convenience.  What vine roots interact with are a suite of varying chemical compounds called minerals, combined in soil with organic matter.  The first three chapters are about these minerals, and Maltman puts particular emphasis on the process by which mineral nutrients become available to vines and other plants: the exchange of ions between soil particles and roots.  The functional differences between mineral assemblies (sand, for example, and clay) is in this respect enormous.  Anyone using the term ‘minerality’ should familiarise themselves with the concept of cation exchange capacity.

This, though, is theoretical knowledge.  Fast forward to chapter nine, where Maltman explains another vital distinction – between geologic minerals (analytically present in rocks and soils) and nutrient minerals (those which are actually bioavailable to vines and other plants).  The bioavailable minerals taken up by vines, he suggests, tend to come from the soil’s organic matter (humus), or from fertilizers.  The percentages of geologic minerals that are bioavailable in bedrock or soil are small or tiny, meaning that the elaborate coverage they receive in much wine literature is of anecdotal interest only.

Soil pH affects nutrient uptake dramatically, and vines themselves have an armoury of selective devices to modify nutrient uptake.  Fermentation, finally, changes the nutrient content of grape juice, to the extent that “the proportion of mineral nutrients in a finished wine bear only a complex, indirect, and distant relationship to the geologic minerals in the vineyard” (p.176).  Most minerals, he is careful to point out, have no sensual identity of any sort.  Whatever ‘minerality’ is, concludes Maltman, “it is not the taste of vineyard minerals” (p.177).

Although he distances the presence of geologic minerals from finished wine aroma and flavour, he does not underplay the role of the soil (in particular the way in which soil delivers water to vines – see chapter 10), nor does he contest the notion of terroir in itself.  Detailed climate considerations are beyond the scope of his book, but it is significant that in the vital pages 191-95 (‘Bringing It All Together: Terroir’) Maltman alludes to the astonishing significance which tiny nuances in topography and mesoclimate have for vines.  He returns to this theme in the Epilogue to the book, contrasting the easy and accessible simplicity of chanting vineyard geologies as a response to the enigma of flavour with the “patient data collection and analysis … [of] intangible technical details like air velocity, UV intensity, spectral wavelength, and bacterial taxa” (p.213).  It is these, he suggests, which may in the end be the terroir factors that most affect the aroma and flavour of wine.

He is also surely right to fault the complete absence of discussion of rootstocks in most wine writing (rootstocks are those parts of the vine, after all, which actually have a direct relationship with soils and bedrock), and to stress that in general that ‘the action’ of cation exchange and nutrient uptake nearly always happens in soils and not bedrock itself, meaning that the importance of pedology greatly outweighs that of geology in terroir analyses.  The ‘unnaturalness’ of vineyard environments, with their comprehensively modified drainage systems, is another important point noted by Maltman.

In many ways, this is a work of thoroughgoing, patient and measured inconoclasm, and you’ll find examples throughout the book of Maltman skewering groundless assertions, confusions, banalities, stupidities and generalisations connected with vineyard geology and its supposed direct, causal relationship with the sensual character of a wine in what he calls ‘populist writings’ on wine.  He deftly pricks other unscientific balloons when they sail past, such as the ‘gravitational significance’ of the moon on anything much smaller than Lake Huron.

He does not assert a zero relationship between geology, soils and wine character – though I note that the section entitled ‘Science Begins to Show Some Connections’ is a mere three pages long.  He understands the importance of metaphor in communicative writing, by the way, and has no objections to the metaphorical use of geological or pedological terms in wine descriptions – provided such terms are understood as being metaphorical.  He also points out that when rocks or soils do ‘smell’, it is generally due to the organic matter (bacteria, algae and moulds) which film geologic surfaces.

Read this book, in conclusion, to use geological terms with precision and accuracy, and to understand what is and is not possible when a grafted grapevine (rootstock and scion) is planted in topsoil over bedrock, and spends 60 or 70 years growing there in situ.  Read it, too, for one other reason.

You and I both know that compelling differences between wines exist.  We’d like to understand where they come from.  Wine producers have made vast technical strides in viticultural and wine-making techniques over the last half-century – yet, far from delivering some kind of ‘grand qualitative unification’, these advances have simply served to underscore the fact that a few site-variety combinations produce wines of outstanding quality, while most do not.

The easiest answer to this conundrum is to look down to the soil medium and the bedrock: it has a physical presence; its differences can be measured and named; and we love the comforting narrative of ‘sustenance from the soil’ since it seems to chime with our own mammalian identity and nutritional habits — even though plants are very different beings from mammals, and derive most of their nutrition from sunlight and air.

The result is that geology has, cuckoo-like, pushed every other fledgling out of the nest of our primitive understanding of terroir.  As a wine-loving (and wine-making) earth scientist, Maltman is uniquely well-qualified to see the damage caused.  His book is an accessible, carefully argued attempt to redress the balance, to set limits to geological influence, and to rescue some of the other possibilities requiring investigation in our long journey towards the understanding of terroir.


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