Last Updated: 2/2025

Summary:  This article explains the role of mannoproteins in winemaking, detailing their origins, benefits, and practical applications for improving wine stability and sensory characteristics.

Mannoproteins can go by many different names including proteoglycans, protective colloids, or colloidal polysaccharides. Mannoproteins are complex molecules composed of ~90% mannans (a long chain of mannose) and ~10% peptides (short chains of amino acids). Despite containing protein in their name, mannoproteins are primarily polysaccharides.

Mannoproteins are naturally present in the outer layer of yeast cell walls and are released into wine during fermentation (when yeast are growing) and yeast autolysis (when yeast are dying).

The amount of mannoproteins in wine depends on the yeast strain used, the duration of lees contact (sur-lie aging) and how the lees are managed. Longer contact typically results in higher mannoprotein content, especially when techniques like lees stirring (bâtonnage) are used. Alternatively, mannoproteins can be supplemented through mannoprotein products.

Mannoproteins vary significantly in their composition and structure. This difference in composition influences how they stabilize wine, enhance mouthfeel, and contribute to other important wine characteristics. Key differences include:

• Molecular Weight
  Varies from 5 to 800 kDa

• Mannan Chain Length
  Varies across mannoproteins

• Peptide Size and Composition
  Varies from 2 to 50 amino acids*

• Component Proportions
  Varying ratios of mannans and peptides

*Some amino acids are hydrophobic and some are hydrophilic. These properties influence how the peptide chain interacts with other wine molecules.

All mannoproteins have colloidal stabilizing abilities. However, depending on the mannoprotein, they can also provide several side-benefits, including:

• Preventing Tartrate Precipitation
  Mannoproteins alter the shape and size of potassium bitartrate crystals, preventing them from forming larger crystals and keeping the wine clear without cold stabilization.

• Modulating Mouthfeel
  Mannoproteins complex with tannins and polysaccharides, reducing astringency and enhancing body, resulting in a ‘rounder’ mouthfeel.

• Influencing Aroma Intensity
  Mannoproteins can affect the persistence of aromas through interactions with peptides.

• Improving Color Stability
  Mannoproteins can interact with anthocyanins, stabilizing these pigments and preventing color loss.

• Stabilizing Sparkling Wine Bubbles
  Mannoproteins’ hydrophobic and hydrophilic regions help stabilize bubbles, improving bubble retention and persistence in sparkling wines.

All mannoprotein products are unique due the way they’re produced. A number of factors during production affect the impact and winemaking application of the mannoprotein:

• The specific strain of Saccharomyces used

• The growth conditions of the yeast and timing of harvest

• The extraction and purification processes used

• The mannoprotein product formulation

Our R&D and product teams have developed specialized processes to extract mannoproteins from selected yeast cell walls. These methods are designed to preserve the functional properties of mannoproteins so that they are in their most active (not necessarily most abundant) form.

Mannoproteins are versatile tools - some are intended for longer contact times and can be added at the end of fermentation to remain in contact during aging. Others can be added 24-72 hours prior to bottling and do not require racking. While they all contribute to colloidal stability, they may also have secondary effects. As with any post-fermentation products, bench trials are recommended to determine proper dosage and confirm intended impact.

Note: Per TTB CFR 27 24.246, the amount used must not exceed 400 mg/L (3.3 lbs/1000 gal). Not all formulations are 100% mannoprotein, so you may see recommended dose rates above 400 mg/L.

Colloids are a natural part of the wine matrix. ‘Colloid’ is a general term that can encompass many different compounds in wine including tannins, color pigments, tartrates, proteins, and polysaccharides.

Wine’s natural inclination is to find the equilibrium between all these compounds. We consider a wine to be “colloidally stable” when the equilibrium allows all these compounds to stay in solution. We consider a wine “colloidally unstable” when the equilibrium forces some of these compounds out of solution, causing a haze or precipitate.

While typically not detrimental to wine sensory characteristics, colloidal instability can cause visual defects and filtration problems. Furthermore, it is difficult to predict or test for the likelihood of this happening. Also commonly referred to as “protective colloids,” mannoproteins help keep other colloids in solution and contribute to colloidal stability.