Techniques for improving or replacing ageing on lees of oak aged red wines: The effects on polysaccharides and the phenolic composition

Alternative techniques to the ageing on lees are being looked for in order to guarantee the improvements provided by this technique but eliminating its disadvantages. The aim of this work was to study the effect of ageing on lees and other alternative techniques (addition of β-glucanase enzymes to the lees; use of different yeast commercial preparations with or without β-glucanase enzymes; use of non-toasted oak chips; and ageing on lees together with micro-oxygenation) on the phenolic compounds, colour, proteins, polysaccharides and sensorial characteristics of red wines during vinification and ageing in oak barrels for 6 months on two consecutive vintages.     

A new methodology to determine cell wall mannoprotein content and release in wine yeasts

Representing around 40% of the cell wall dry weight, mannoproteins are complex macromolecules structurally composed of polymers of sugar, 98% being mannose, covalently linked to peptides. Along the last two decades, these compounds have gained ground as very relevant molecules in the field of winemaking, mainly due to their positive contributions in the development of appreciated organoleptic features and to their contribution in the chemical stabilization of wine. Several methodologies have been recently proposed to achieve the quantification of these compounds. However, these methodologies are laborious, time consuming and do not allow a global quantification of these macromolecules. In this paper, an easy, reliable and fast forward methodology for the quantification of mannoproteins in model must is proposed and evaluated. Its application in the quantification of mannoproteins content in yeast cell wall is also demonstrated.     

Role of lees in wine production: A review

The sometimes contradictory role attributed by scientists to lees in wine production is discussed in this review. Studies dealing with the importance of lees in the natural removal of undesirable compounds from wine, the effect of lees–wine contact on the volatile fraction of wines, the key influence of lees on biogenic amine contents in wines, the interactions between lees and phenolic compounds, and the importance of mannoproteins and lipids released by lees have been critically reviewed. Finally, the present exploitation of lees is also outlined.     

Effect of commercial mannoproteins on wine colour and tannins stability

Commercial oenological products containing mannoproteins have the purpose of preventing tartrate salts precipitation or achieving wines with a better mouth-feeling. The evaluation of the influence of three commercial mannoproteins on colour and tannin stability of three different red wines (two from Touriga Nacional and one from Alfrocheiro and Aragonês varieties) was studied. The evolution of colour through time was similar for all modalities, resulting in an increase of polymeric pigments and colour hue and a decrease of other parameters, suggesting that there was no influence of commercial mannoproteins on colour stability. The tannin profile evolution showed a possible stabilizing effect of one of the commercial products for tannins with an mDP between 8 and 14. It is possible that the commercial mannoproteins used in this work have some influence on the tannin aggregation evolution, contributing to the delay of tannin polymerisation in red wines.     

Nitrogen compounds and polysaccharides changes during the biological ageing of sherry wines

Biologically aged sherry wines are elaborated by the so called “criadera” and “solera” system, which essentially involves development of the yeast on the wine surface forming a film velum for several years. In this work, a study on the changes that take place in polysaccharide and nitrogen compounds during the elaboration of sherry wines has been undertaken. The evolution of monosaccharides derived from polysaccharides as well as of amino acids and polypeptides have been investigated in wine samples at different stages of the elaboration process (young wines, “sobretablas”, “criaderas” and “solera”). Mannose, galactose, glucose and arabinose were detected in all analyzed wines; mannose being the most abundant carbohydrate, particularly in wines that aged longer. Glucose and galactose content also increased during the biological ageing of these wines, whereas arabinose concentration lowered during all period. Nitrogen compounds experimented a decrease and even some amino acids were not detected at the end of the ageing. Considering the increase in mannose and the decrease in amino acid levels, it is presumable that autolysis and growth of yeast occur at the same time during the elaboration of the sherry wines.     

Interactions between aroma compounds and whole mannoprotein isolated from Saccharomyces cerevisiae strains

The interactions of four wine aroma compounds (isoamyl acetate, hexanol, ethyl hexanoate, β-ionone) either with a whole mannoprotein extract or with mannoprotein fractions at a level encountered in wine (150 mg/L) were studied by dynamic and static headspace techniques. The mannoproteins were isolated from a synthetic medium subjected to an alcoholic fermentation with two enological yeast strains. They were fractionated by exclusion chromatography and characterized through glycosyl composition analysis.