What is sur lie ageing, and what does it do to wine?

Sur lie ageing is a winemaking process where wine ages in contact with lees (dead yeast cells). The process adds flavour, texture and stability to wine, with lees contributing to a buttery mouthfeel, increased complexity and specific aromas like brioche and toasted nuts. Winemakers differentiate between gross and fine lees, managing the ageing process accordingly. Sur lie ageing is common in sparkling wines like Champagne as well as in white wines like Muscadet and Burgundy. The process can also be used with red wines for specific benefits. Ageing ‘sur lie’ (the french for ‘on the lees’) is an important tool at the disposal of winemakers. It’s integral to the character of multiple wines, and even to the core identity of certain appellations and styles. But what are lees and what’s the impact of ageing wine in their presence? [subscriber-content] Yeasty bits Lees – an old English term for sediments deposited at the bottom of a vessel – are mostly made up of dead yeast cells, a byproduct of alcoholic fermentation. Undisturbed, they will naturally decant to the bottom of the fermentation vessel during and after the process. Winemakers generally differentiate between gross and fine lees, an important distinction because the different size indicates sediments of different nature – and with different outcomes if left in contact with the wine during ageing. Gross lees refer to larger particles, namely yeast cells, both dead and viable, and cellular matter (pieces of skins, stems, and seeds leftover after fermentation) from the grape. Fine lees are smaller, taking longer to precipitate and interact with other compounds in the wine. The latter are associated with desirable impact on the final wine, while the former can lead to the development of undesirable aromas and flavours. Following alcoholic fermentation winemakers decide whether they will separate the wine from the sediments or let the lees remain inside the vessel where the wine will age, either for the whole or partial duration of the ageing process. It is common to restrict the time spent on the gross lees while allowing the wine to spend longer in contact with the finer particles. Most commercially available wine, produced for quick bottling and immediate consumption, will be separated from the lees shortly after alcoholic fermentation is completed, clarified and stabilised. So what happens if, otherwise, the wine is left ‘sur lie’ for a given period? Moreish transformation If managed correctly, allowing the wine to age in contact with its lees can add multiple flavour, textural and structural benefits to a wine. The dead yeast cells that make up most of the lees will go through a process of autolysis, i.e. their internal structures will be destroyed by their own enzymes. This process releases sugars and peptides that will contribute to an unctuous, buttery mouthfeel in the final wine, while some proteins bind with tannins (if these are present) adding to the velvety texture. Overall, the wine becomes chemically more stable: mannoproteins reduce tartrate precipitation and promote protein stability; oxidation is inhibited by the release of sulphur compounds and reducing enzymes – which can be unpleasant if left to dominate. This issue can be managed by removing the gross lees early on and also by performing bâtonnage. Also known as lees stirring, bâttonage prevents the accumulation of hydrogen sulphide and also ensures that the wine has homogenous contact with the lees (on the other hand, by increasing liquid/lees contact surface the bâttonage will encourage greater unctuosity and lees ageing-induced aromas). [caption id="attachment_465230" align="alignnone" width="630"] Tool used for stirring lees during bâtonnage, credit Per Karlsson, BKWine 2 / Alamy Stock Photo[/caption] Increased stability explains why ageing on the lees is a resource commonly used by low intervention winemakers, as it decreases the need for the wine to undergo clarification and/or stabilisation processes to become stable and ready to bottle. In addition to the creaminess mentioned above, some flavours – acacia, oatmeal biscuit, brioche, bread dough, toasted nuts – are telltale of sur lie ageing. Again, these are a result of the present of complex protein molecules that serve as their precursors. Furthermore, lees encourage malolactic fermentation as they serve as micronutrients for the lactic bacteria that perform it. By promoting this process, lees further contribute to the unctuosity and butteriness of the wines. Champagne, Muscadet and beyond Ageing on the lees requires technical knowledge, sensibility as well as the acknowledgment of the desired style of wine produced. It can take anywhere from a few weeks to a few months or years, depending on the viticultural region and specific winemaker preference. The style by far more associated with ‘sur lie’ ageing is traditional method sparkling, with all leading appellations – Champagne , Cava , Franciacorta etc – defining minimum ageing ‘sur lie’ requirements determining how long tye wines will rest in the bottle, in contact with the lees, following secondary alcoholic fermentation. This accounts for the distinct bready and nutty aromas so strongly associated with premium champagnes. Other wines and regions, such as Muscadet , Burgundy and Burgundy-inspired Chardonnays around the world also owe their identity and trademark flavour profiles to the processes, described above, promoted by the presence of lees during a given period of the wines’ ageing. While more commonly associated with white and sparkling wines, reds can also be aged sur lie, not least when textural appeal, tannin management and colour stability are a concern. [/subscriber-content] Related articles What does 'vintage' mean? Why are there crystals in my wine? What is white port?

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