Loire Valley Wine Guide: White Winemaking, Fermentation & Élevage
In this second instalment of my guide looking at white winemaking in the Loire Valley I move on from picking and pressing to look now at fermentation and élevage. As I explained in my introduction to part one the aim here isn’t to provide a comprehensive guide to every facet of winemaking that exists, as to do so would require that we all enrol on a degree course (maybe at the lycée at Montreuil-Bellay) and digest several textbooks along the way. Instead, this short series of articles should be regarded as a simple framework looking at the very basic decisions undertaken by the average Ligérian vigneron, spiced up along the way with details of some of the more quirky, quizzical or controversial practices.
There are many differences between how white and red grapes are vinified. Perhaps key is that in the vast majority of cases the white grapes (whether already destemmed, usually by a picking machine, or in whole bunches) are pressed first, and then the juice fermented. With red grapes, however, juice, skins, pips (and maybe stalks, depending on the variety and the methodology) are fermented together. As we are focusing on white wines here, suffice to say after the pressing the next decisions concern the vinification of the juice. Although the core of this process is the fermentation, there are other critical steps which come immediately before and after fermentation that we should not overlook. One of these is settling.
The juice obtained from pressing grapes is not the crystal clear nectar you might imagine it to be. In truth it is more likely to be a swirling, turbid concoction of grape juice and associated solids, including grape pulp, fragments of grape skin, pips and even the occasional stalk that has slipped through the press. Prior to fermentation it is commonplace to leave this suspension in a vat overnight to settle, often refrigerated (typically to between 5ºC and 10ºC) in order to maintain its freshness and to stave off fermentation. The more industrial winemaker may add pectolytic enzymes to aid the degradation of these solids and improve the clarity of the juice.
Pectin (to be precise I should write ‘pectins’ as there are a number of molecules that fit the bill) is the ‘glue’ that holds plants together. Between the cells is an extracellular matrix which helps them adhere to one another, and the pectins are an important part of this mix. As grapes ripen, pectin levels gradually climb, ensuring the integrity of the berries as they swell with the sweet juices, and after pressing there may be as much as 1 gram of pectin in every litre of grape juice. Adding pectolytic enzymes thus disrupts the solid particulates, decreasing juice viscosity, and aiding settling. Some technically-minded winemakers who are really in a hurry might even add a fining agent to further speed up settling.