Sweet Mysteries

Sources of Sugar in Grapes:

• Wine is made from the fermentation of two main grape sugars: glucose and fructose.

• These sugars are the most abundant in grapes, usually found in near-equal amounts, but ratios can vary due to climatic and varietal differences.

• Other sugars like sucrose and various polysaccharides are also present in grapes but in smaller quantities.

• Sugars in Wine:

  • In wine, yeast primarily metabolizes glucose and fructose.

  • Sucrose, if present, is usually hydrolyzed into glucose and fructose and is thus rarely found in finished wine.

  • Pentose sugars (like arabinose xylose) are not metabolized by yeast and remain in the wine, contributing minimally to sweetness.

• Yeast and Sugar Metabolism:

  • Yeast prefers glucose over fructose, which can lead to imbalances in their ratio towards the end of fermentation.

  • This imbalance can affect the fermentation process and the perceived sweetness of the wine.

• Sugar Analysis in Wine:

  • Key reasons for sugar analysis in wine include ensuring fermentation completion, determining sweetness, and regulatory labeling requirements.

  • The focus is primarily on measuring glucose and fructose, as they significantly influence wine sweetness.

  • Modern analytical methods like enzymatic analysis and high-performance liquid chromatography (HPLC) are preferred for accuracy.

• Challenges with Traditional 'Reducing Sugar' Methods:

  • Older methods based on the 'reducing sugar' concept can lead to inaccurate results due to non-specificity and interference from other wine components.

  • Such inaccuracies can lead to mislabeling and regulatory compliance issues.

• Regulatory Considerations:

  • Some regulatory authorities still use outdated methods, necessitating careful method selection to ensure compliance.

  • International efforts are underway to standardize regulatory frameworks on glucose and fructose analysis methods in wine.

This review provides a detailed understanding of the importance of sugar analysis in wine production, emphasizing modern techniques for accuracy and compliance with regulatory standards.