There is no doubt that the quality of wines produced today has vastly improved over the wines of yesteryear. This refinement of wine production, much like the understanding of Barrel Types, has been a direct result of extensive research, providing a greater understanding of how to manipulate the grape itself. Ever since the first bottle of wine was corked, vineyards and wineries have constantly sought ways to make their wine better. So they started where all great bottles of wine start, with the sugar content of the grape itself.
There are four distinct parts of a grape; skin, flesh, seed and vascular bundles. Each part plays a significant role in the overall composition of the wine produced. Along with breaking the grape down into four distinct parts, scientists have also researched the periods when acids and sugars accumulate in the grape. This is critically important to understanding how viticulture practices can be used to modify wine styles.
Every grape has two distinct growth periods, separated by a lag phase, during its development. The first phase starts with the bloom and last for approximately 60 days. This phase is characterized by grape formation and the production of seed embryos. The seeds contain the genetic material of the vine and its reproductive success depends upon the survival of those seeds. Also during this phase the grape expands in volume as solutes accumulate. The most prevalent solutes are tartaric and malic acid. Tartaric acid levels are highest towards the outside of the developing grape, and malic acid levles are highest in the flesh.
The second growth phase begins after the lag phase and lasts until harvest. During the second growth phase the grape will approximately double in size . Tartaric and malic acids remain at harvest, but due to the increase in berry volume and sugar content, the overall concentration is decreased.
Sugars are transported from the vine into the grape and make sure the seed has enough energy to live. As vine and grape development continues the surrounding leaves begin to supply the majority of the sugars the grape seeds consume. The most prevalent sugar is sucrose, which is a glucose and fructose molecule bonded together.
Sugars are mainly stored in the flesh of the grape. Smaller amounts are stored in the skin which impact the levels of tannins in the resulting wine. It was discovered that the highest concentration of sugars is in the flesh nearest to the skin. The abundance of grape sugar makes it easy to extract, and provides for the building blocks of alcoholic fermentation.
Choosing the correct terroir for each grape type greatly impacts those building blocks. Grapes are very sensitive to temperature and its fluctuations. For some grape types, weather that is too warm will cause the grape to develop too quickly and will also dilute flavors and the delicate balance between sugars and acids. Weather that is too cold will cause the grape to under-develop and produce a grape high in acid and low in sugars.
In the end, the total sugar content of a fully ripened grape is totally dependent on viticultural practices and terroir. Based on a harmonious mix of these elements, the sugar content at harvet can range from 12% to 28%. Allowing a grape to ripen past its maturity changes the concentration of the sugar, but not the total sugar content.
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