Grape Berry Composition at Harvest

I'm rereading my notes, trying to remind myself of things I've already learned. In the UC Davis Wine Production course, we learned that the grape berry at harvest is comprised of the following components in the approximate distribution found below:

• Sugar                   200 grams/liter
• Organic Acids        10 grams/liter
• Amino Acids             5 grams/liter
• Phenolics              2-5 grams/liter
• Volatiles                       trace
• Water                   800 grams/liter

For each of the above components, the most prevalent compounds found in the grape berry are:

• Sugar: glucose and fructose
• Organic Acids: tartrate and malate
• Amino Acids: glutamate, glutamine, alanine, arginine and proline
• Phenolics: caftaric acid
• Volatiles: terpenes and esters

Although the primary carbohydrate produced in the grape is sucrose, there is an enzyme called invertase that splits the sucrose into it's components, glucose and fructose at the point of entry into the grape berry. This keeps the concentration of sucrose on the outside of the grape, ensuring that glucose and fructose will accumulate in the grape. As the grape goes through veraison, the concentration of malate decreases as this compound is being used as an energy source, again ensuring that glucose and fructose remain in the grape.
The phenolic compounds exists mainly in the grape skin and seeds. It's location in the skin is to protect the grape from microbial attacks. In addition, the grape berry contains trace elements including cations and anions. One of the important grape cations is potassium, found in the highest concentration in the skin of the grape.¹
Link to: Grape Berry Diagram²
1. UC Davis Online Course: Wine Production, VID252, Lesson 2.
2. Understanding Grape Berry Development Practical Winery and Vineyard, Issue July-August 2002, Illustration done by Jordan Koutroumanidis of Winetitles.