Lees

Definition - What does Lees mean?

Lees are deposits of dead yeast cells and grape material in the bottom of the fermentation barrel. They can be removed after primary fermentation (a process called “racking”) or left in the wine to impart further flavor and textural qualities to the wine (a process called “sur lie” or “lees aging”).

There are two types of lees, gross lees and fine lees. Gross lees is large sediment that is usually removed after primary fermentation. Fine lees is the creamy sediment made up of small particles. When a wine is aged “sur lie”, it is aged on fine lees.

WineFrog explains Lees

As a wine ferments, the different particles and chemicals react to one another, bonding and separating to create larger particles. The larger particles, heavier than the wine itself, sink to the bottom to be removed from the wine. These particles are called lees and can be separated into two types: gross and fine.

Gross Lees

Also known as heavy lees or grape lees, these are large chunks that form around primary fermentation.

In red wine:

  • Vegetal particles (grape skin, stems, pulp, pieces of seed)
  • Combinations of tartaric crystals, yeast, coloring matter and precipitated tannins
  • Flakes from reactions between proteins, polysaccharides and tannins during maceration

In white and rosés:

  • Vegetal particles (grape skin, stems, pulp, pieces of seed)
  • Combinations of tartaric crystals, yeast, precipitated colloidal matter,
  • Particles of fining and clarification treatments: bentonite, casein, PVVPP, etc.

Gross lees can form throughout the wine’s maturation. Winemakers have to carefully monitor gross lees as they have the most potential to damage a wine. For example, the vegetal matter could rot, imparting negative, vegetal characteristics. Winemakers usually remove as much of the gross lees as they can after primary fermentation.

Fine Lees

Also known as light lees or yeast lees, these smaller, fine, creamy particles coat the bottom of the fermentation vessel during secondary fermentation and aging. In all types of wine, fine lees are composed of dead or residual yeast particles and lactic bacteria residue.

Fine lees are used in sur lie aging. They add complexity, texture and structure of a wine. Though there is less risk with fine lees, the winemaker must still monitor and stir the wine to ensure the dead yeast cells don’t rot and release sulfur like notes.