Sur lie (in Japanese Koshu)

What It Is

Sur lie (French for "on the lees") is a winemaking technique in which a finished still white wine is held in tank or barrel without being racked off its fine sediment — dead yeast cells, fruit solids, tartrate crystals — for several months after fermentation. The lees slowly autolyze, releasing mannoproteins, polysaccharides, and amino acids into the wine. The result: more body, a creamy texture, gentle reductive aromatics, and longer aging potential.

The technique is most famously associated with Muscadet (the Sèvre-et-Maine appellation in the western Loire). It also appears in Burgundy whites, Champagne (which is sur lie aging on lees plus secondary fermentation), and a handful of New World whites.

The Mercian Story

In 1983, Mercian winemaker Usuke Asai (麻井宇介) introduced sur lie aging to Koshu winemaking. The motive was simple: Koshu in its conventional 1970s style was thin, sometimes oxidative, often described in international tastings as "lacking body." Asai had studied in Bordeaux and observed how Loire winemakers used lees contact to add weight without oak. He applied the idea to Koshu and found it transformed the variety.

The resulting wine — fermented and aged in stainless steel, kept on its fine lees for three to six months, then bottled — had texture, mid-palate density, and a savory (umami) quality that conventional Koshu lacked. Mercian named it "Koshu Sur Lie" and the style swept Yamanashi within a decade. Today essentially every serious Koshu producer makes a sur lie cuvée, and the technique has become the variety’s default modern signature.

Why It Matters

Two reasons:

1. Style breakthrough. Sur lie made Koshu international-quality. Without it, Koshu would arguably still be a curiosity wine — interesting historically, thin in the glass. 2. Cultural marker. The technique is a clear example of Japanese winemakers borrowing a European method and adapting it to a Japanese variety, rather than blindly copying European varieties or sticking to fortified-style traditional methods. It is one of the cleanest examples of Japan’s "we will learn, then localize" approach.

Asai went on to write the canonical Japanese-language texts on modern Koshu winemaking. He passed away in 2002 but is widely credited as the intellectual force behind postwar Japanese Koshu.

Details

• Origin: Muscadet, Loire Valley
• Adopted for Koshu: 1983, Mercian, by winemaker Usuke Asai
• Effect: Adds body, texture, savory umami; reduces overt oxidative character
• Common duration: 3–6 months on fine lees