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Mannoproteins - How are they used in winemaking?

Introduction

Mannoproteins are a naturally occurring group of proteins found in the cell walls of yeasts. In particular, the mannoproteins in the wine yeast Saccharomyces cerevisiae have been studied extensively. The beneficial winemaking properties of mannoproteins, including tartrate stabilisation, are discussed in this article.

Properties of mannoproteins

It has been observed for many years that wines aged on lees are more stable for both potassium bitartrate and protein haze, and certain mouthfeel characteristics are well known. These effects are in large part due to the mannoproteins that are released from the yeast cell wall during autolysis.

The tartrate stability properties of mannoproteins have been studied extensively over the past few years. One study has shown that mannoproteins have tartrate stability effects (Lubbers). Further similar studies have confirmed that wine aged on lees can become tartrate stable and therefore do not require cold stabilisation (Ribéreau- Gayon et al., 2000 b).

The effect on reducing the formation of tartrate crystals appears to be due to the inhibition of the formation of crystal nuclei - the first step in crystal development. The colloidal effect of these mannoproteins has been studied and when they have been removed from wine the tartrate stability does decrease (Moutounet et al.,1999).

Some manufacturers have been active in taking advantage of this knowledge and some commercial mannoprotein products have been developed and have been approved for use in winemaking in Australia for several years.

Potassium bitartrate stability

Potassium bitartrate (also known as Potassium Hydrogen Tartrate, KHT) is a naturally occurring salt that is formed under certain conditions in wine. It is unstable and can form crystals in wine and has decreased solubility in the presence of ethanol. As the wine ferments and the ethanol content increases, the KHT becomes increasingly insoluble and readily forms crystals. The temperature of the wine is a critical factor in this instability, as are tartrate ion concentration, potassium and calcium concentrations, pH and presence of colloids.

Methods of achieving Potassium bitartrate stability

There are several techniques that have been used for KHT stabilisation in wine.
In historical order they include:

  • Addition of metatartaric acid
  • Cold stabilisation
  • Electrodialysis
  • Mannoprotein addition
  • Addition of carboxy methyl cellulose (CMC)

No one technique is ideal - all these methods have their advantages and disadvantages, however the main technique used in Australia is cold stabilisation. The right technique will depend upon the individual situation that the winemaker finds him/herself in.

The use of commercial mannoprotein products is very promising as there are a number of benefits when compared to the more traditional cold stabilisation technique.

Benefits of using mannoproteins for tartrate stability of wine

A study was performed by Provisor in 2009 on the DSM mannoprotein product Claristar, to validate its use in Australian wines. To quote from the article:

Claristar has been successful in preventing the formation of KHT crystals with a wide range of white wines... In general, a recommended dosage rate of 100mL/hL was effective in preventing KHT crystallisation”

The benefits of using such a product include:

  • mannoproteins are naturally occurring in wine
  • commercial products, such as Claristar, can be simply added in liquid form
  • extra mouthfeel enhancements can also be obtained
  • no chilling of wine is needed and so potential sensory impacts are avoided
  • expensive and less environmentally friendly electricity-based stabilisation techniques can be avoided
  • no special plant is needed for KHT stabilisation as is the case with cold stabilisation or electrodialysis

What are mannoproteins?

Mannoproteins are naturally occurring proteins that are found in yeast cell walls. In Saccharomyces cerevisiae the cell wall is composed mainly of polysaccharides (glucans and mannans), but also contains proteins, in particular mannoproteins.
Wine naturally contains mannoproteins as they are released during yeast fermentation and then later during yeast autolysis.
 
Mannose, a naturally occurring sugar, is one of the basic building blocks of mannoproteins. Mannose is very similar in structure to glucose. The other main component of mannoproteins is a polypeptide (protein) backbone chain from which the highly branched mannose side chains are linked by glycosidic bonds. They are large molecules with molecular weights as high as 800,000 Daltons. As such, mannoproteins can they have diverse structures and therefore a diversity of properties.

Conclusion

Mannoproteins are a natural component of winemaking and are present during yeast fermentation and aging on lees. The mannoproteins are naturally extracted from yeast cell walls. The chemistry of these proteins has been well studied and the beneficial properties confirmed. Commercial products, such as DSM Claristar, have been developed by extracting very particular fractions from Saccharomyces cerivisiae. These products are now used in many wineries to improve tartrate stability and to enhance mouthfeel of the finished wine without the cost or environmental impact of high electricity usage.

Article from the  Australian and New Zealand Grapegrower and Winemaker, Issue 587, 2012
Page Number(s): 74

Author: Greg Howell

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