WSET diploma intro Flashcards
Components of the grape
Describe PHOTOSYNTHESIS
A biochemical process by which green plants are synthesizing sugars (sucrose) from carbon dioxide and water with the aid of chlorophyll and energy from sun and warmth.
6 CO2 + 6 H2O + light –> C6H12O6 + 6 O2.
Describe the difference between SUCROSE, GLUCOSE and FRUCTOSE
Sucrose is produced in the leaves to be transported to grapes, which are the storehouses. Due to presence of acids in the grape it is broken down into glucose and fructose.
Fructose is the sweetest, followed by sucrose, and glucose being the least sweet.
Yeast prefer glucose and eat it first; fructose is the main sugar in sweet wines.
Name 2 tools used to measure sugar content
Refractometer and hydrometer.
Name 2 main acids found in grapes
Malic and Tartaric
Describe malic acid
Principal acid of apples (latin for apple is “malus”);
Sharp taste;
Present mostly in very young, green grapes;
Consumed by the grape as an energy source;
Converts into glucose in gluconeogenesis process - proportion of malic acid in the grape goes down as maturity approaches.
-released in 1st pressing
Describe tartaric acid
Unique to grapes;
Found in most finished wines;
Formed as a by-product of the synthesis of sugar;
Latin for deposit is “tartarus”: forms deposit in containers;
Quantity of tartaric acid in grape rises in proportion to the creation of sugars.
-released in 2nd pressing
Describe what happens to tartaric and malic acid in the maturation of the grapes
Malic acid is destroyed biochemically;
Tartaric acid becomes diluted in raising sugar levels.
How do you measure acid levels
Simple TITRATION - Titratable acidity
How the grape vine picks the mineral salts?
By the roots, as they delve deep in the subsoil in search of the moisture
Which minerals and why are the most abundand
Salts of potassium (K), they are associated with the production and translocation of the sugars; its concentration rises with the accumulation of the sugars in the grape.
What is negative influence of the minerals to the final bottling product?
Formation of potassium bi-tartare and other crystal formations.
List 5 most important minerals in grapes
- Salts of potassium (K)
- Calcium (Ca)
- Magnesium (Mg)
- Iron (Fe)
- Copper (Cu)
Describe relation between mineral salts, acids and pH.
Actual taste of wine is determined by pH of the juice, not the acidity. pH is controlled by the interaction between the acids and the salts.
Presence of certain salts can change the degree of acidity of the acids - “buffering”.
List 2 main classes of phenolic compounds
Flavonoids (polyphenols) and non-flavonoids (small, little influence on the finished wine)
What is the most important role of polyphenols (flavonoids)?
Antioxdiation: preservance of the wine and the winedrinker.
How can we sub-divide polyphenols
Into tannins and anthocyanins.
Where do we find tannins in grapes?
In skins (tough outer layer), stems and pips.
What are anthocyanins responsible for?
Colour in red and rose wines.
Where are anthocyanins found in grapes?
In the softer sells towards the inner layers of the skin grape.
How is the colour of red and rose achieved?
By extraction anthocyanins from the skins during the fermentation: alcohol extract anthocyanins from the skins;
The thicker skins, the more colouring matter.
Extraction can be done also by the heat, breaking down the cells walls.
Describe the colour changes connected with maturation of wine.
There are also other pigmented compounds –> during aging ratio of them changes: bluer one diminishes, so wine change from purple to orange.
Anthocyanins are not chemically stable;
With age anthocyanins link with tannins forming more stable pigmented polymers.
+ further reactions between anthocyanins and other phenolic compounds and aldehydes