The Best Grapes Make the Best Wine
It's harvest time in Southern California! You can feel the excitement on the vineyards. Winemakers are in the field testing grapes, anxiously waiting on the perfect Brix and pH levels that indicate it is time to harvest. Crews are ready to work throughout the night hand picking clusters of grapes.
As a crop advisor with a fascination with winemaking, I thought it would be fun to dive deeper into the plant compounds responsible for the aromatics and flavors that make great wine. This is also an opportunity to explain how regenerative practices play a significant role in the quality of wine.
Focusing on soil health and cultural management provides immediate benefit to vineyard health and the quality of the grapes. I see a major economic benefit for the Southern California AVAs if vineyards work together to improve soil ecology, consistency and collective value of their varietals.
I was inspired to research secondary plant metabolites after taking a few courses at Regen Ag Academy and I found a fantastic article by Ali, Kashif et al. “Metabolic constituents of grapevine and grape-derived products.” Phytochemistry reviews : proceedings of the Phytochemical Society of Europe vol. 9,3 (2010): 357-378. doi:10.1007/s11101-009-9158-0
How does soil quality affect a wine’s expression?
The taste and mouth-feel sensations in wine are primarily due to compounds like water, ethanol, organic acids, amino acids, sugars, and glycerol.
Primary metabolism is directly involved in normal growth, development, and reproduction of plant species. Plant metabolic pathways like photosynthesis, protein synthesis, and lipid production require specialized proteins that soil microbes use to make nutrients available for microbial and plant uptake (enzymes), and trace mineral metals or B vitamins required for an enzyme to perform its function (enzyme cofactors).
Adequate nutrient concentration in the leaves form complex carbohydrates, called polysaccharides during photosynthesis. The majority of photosynthates are transported through the phloem into sugar sinks (roots, grapes, new shoots) in the late afternoon. Photosynthates are transported to the roots to form exudates where they are metabolized between 2 am and 8 am.
Exudates containing mostly polysaccharides improve soil health. They tend to produce a disease suppressive microbiome. Polysaccharides attract beneficial microorganisms in the soil that are responsible for improved nutrient cycling, and formation of secondary plant metabolites. Vines with nutrient deficiencies and imbalances produce root exudates primarily composed of monosaccharides can enhance soil borne diseases.
- A brief overview of Primary Metabolites:
- Researchers have concluded that the composition of amino acids in grapes contribute to wine aroma, taste, and appearance. (Escudero et al. 2000). In the winemaking process, nitrogen sources are metabolized by the yeasts and modify the consumption of amino acids and ammonium in the juice thus causing a variation in the wine aroma. As occurs with esters, the pool of intracellular nitrogen regulates the formation of higher alcohols (Large 1986).
- Polysaccharides are partially water soluble and extracted into the juice during crushing and pressing. The effects of polysaccharides in wines contribute to the "mellowness" or by modulating astringency.
- Alcohols- Ethanol is the most abundant and important alcohol in wine. Ethanol concentration in wine generally ranges from 10 to 16 ml/100 ml, depending mainly on sugar content and lesser on temperature and yeast strain. Ethanol is crucial to the stability, aging, and sensory properties of wine. It also influences the type and amount of aromatic compounds produced by affecting the metabolic activity of yeast. The dissolving action of ethanol is also probably involved in the reduction of the evaporation of aromatic compounds during fermentation (Williams and Rosser 1981).
- Organic Acids- In grape juice and wine, organic acids composition is very important. The major organic acids are tartaric and malic acids. Grapes also contain succinic and citric acid in low amounts.
Secondary Plant Metabolism
Secondary plant metabolites such as phenolics, terpenes, phytoalexins, and tannins are not directly involved with developmental processes. They are responsible for important ecological functions like defenses against predators, parasites and diseases, for interspecies competition, and to facilitate the reproductive processes (coloring agents, attractive aromas, etc.)
- Phenolics are responsible for aroma, also known as the olfactory component of taste. Aromas are comprised of individual compounds that are likely to play a very important role in the human taste perception. The terpenes, carbonyls, phenols, lactones, acetals, hydrocarbons, sulfur, and nitrogen compounds, although present in very low concentrations, contribute to the fragrance of wine.
- Phytoalexins are substances produced by plant tissues in response to contact with a parasite and specifically- inhibits the growth of that parasite. In grapevines, the best characterized defense mechanisms are the accumulation of phytoalexins and the synthesis of pathogenesis related proteins. Particular attention has been given to stilbene phytoalexins (e.g. resveratrol) produced by Vitaceae.
Plant Immune Systems
Nutrient management plays an important role in the suppression of pathogens. It creates two types of immunity (passive and active) to pests and pathogens. Passive immunity is a result of a plant that no longer contains the compounds needed as a food source by potential pests. Active immunity occurs when plants develop high concentrations of secondary metabolites such as phytoalexins, terpenes, and tannins which actively combat potential infections of bacteria, fungi and insects. Nutrient storage in the form of phospholipids helps create an impermeable layer on the leaf surfaces to protect against airborne infections like powdery mildew, crown gall and others. The cuticle layer and cell wall physically resist the penetration of hyphae while tannins and phenolics inhibit fungal enzymes involved in pathogenesis (Goetz et al. 1999; Sarig et al. 1998).
Would you like to have a conversation about how to implement regenerative agriculture practices on your vineyard?