2.5 Grape Development Flashcards
When is Grape Development in the Northern Hemisphere?
June–October
When is Grape Development in the Southern Hemisphere?
December–April
What are the four stages of grape development?
- Grape Berry Formation
- Veraison
- Ripening
- Extra-Ripening
Describe berry development during the Early Grape Growth phase
Small green berries start to grow in size
- tartaric and malic acids accumulate.
- Some aroma compounds and aroma precursors (methoxypyrazines) dev
- Tannins accumulate (very bitter)
- Sugar levels are low in this phase
- Water flow into grape is high in this phase
What are methoxypyrazines?
What wines would you find them in?
Methoxypyrazines are aroma precursors
- develop into herbaceous aromas/flavours
- in wines, such
Sauvignon Blanc, Cabernet Sauvignon and Cabernet Franc.
What causes a prolonged grape berry development period? Why? Why can this be harmful?
- Too much water and nitrogen encourage shoot growth in preference to grape ripening
- Causes delay in the onset of the ripening stage
- May not be sufficient time for ripening before weather changes ~ harvest time
What speeds up the grape berry development period? Why? Describe the result in the final wine.
Mild water stress
- Leads to smaller grapes
- Reduces juice yield
- Greater skin to pulp ratio (can be associated with better quality in red wines - higher levels of colour, tannins and aroma compounds)
Describe Veraison?
- Grape growth slows down (lag phase)
- Grape cell walls become stretchy and supple
- Green-coloured chlorophyll in skin cells is broken down - black grapes start to become red in colour due to the synthesis of compounds called anthocyanins
What does the vine need during grape development?
- Sunlight
- Warmth
- Mild water stress
What are adverse conditions during grape development?
- Too much water and nutrients
- Excessive shading of grapes
- Very cold or very hot conditions throughout the day and night
When does shoot growth start to slow down?
At the start of the ripening phase.
What stage marks the end of ripening?
Harvest
When is Harvest in the Northern Hemisphere?
Sept–October
When is Harvest in the Southern Hemisphere?
March–April
What changes take place within the grape during the ripening phase?
- Sugar and water accumulate
- Acid levels fall
- Tannins, colour and a number of aroma precursors and aroma compounds develop
What is the temperature required for Photosynthesis to occur at the maximum rate? What amount of sunlight is required?
- 18–33°C (64–91°F)
- 1/3 of full sunshine
What amount of sunlight is required for Photosynthesis?
- Sunlight levels that are above one third of full sunshine
What effect do warmer years with extreme heat and dry conditions have on photosynthesis and thus, on the vine?
- in extreme heat, or water stress the stomata close. - This pauses photosynthesis and therefore the production of sugar - sugar will not be accumulated as expected.
- In severe cases the vine shuts down and may die.
How do the grapes develop sugar?
- Sugar is produced in the vines’ leaves by photosynthesis
- A sugar solution is transported by the phloem into the grapes
In what conditions is the rate of grape transpiration faster? In what conditions is it slower?
Faster = warm, dry conditions Slower = cool, humid conditions
How does the concentration of tartaric acid change during ripening?
- Total amount of tartaric acid in the grape generally does not change
- However concentration falls during ripening due to dilution, as sugar and water accumulate in the grape
Why do wines from cooler climates tend to have higher natural acidity?
- Malic acid is metabolised in respiration during the ripening stage
- Respiration is slower at cool temperatures than warm ones
- Cool night time temperatures also mean that less malic acid is lost during respiration
During the final month of ripening, what temperature range is crucial? What happens if it’s too warm? Too cool?
Mean Temperature between 15° and 21° C (59 - 70 F)
- Warmer than 21°C : rapid loss of acidity (rapid transpiration)
- Cooler than 15°C: acidity levels are too high (slower transpiration)
What happens to methoxypyrazine levels during ripening? What conditions can hinder this?
- Levels fall
- Cool temperatures and limited sunlight (e.g. due to excessive shading of bunches) can hinder this decrease and the resulting wines may show particularly herbaceous aromas/flavours
What aroma compound increases during ripening? What types of aromas does this compound give off?
- Terpenes
- Give floral and citrus aromas such as the grapey aromas found in Muscat
What conditions give off ‘riper’ aromas?
Warmer, sunnier climates tend to produce grapes and wines with aromas that could be described as ‘riper’ than cooler, less sunny climates.
What role does Tannin play in defining Ripeness and “ready for harvest”
- Producers wish to avoid unripe tannins - tannin ripeness is an important parameter for deciding if grapes are ready for harvest.
- Sunshine on grapes is essential for
- -accumulation of tannins pre-veraison
- -polymerisation of tannins post veraison (means they become less bitter)
Polymerisation is the process in which small molecules chemically combine to form large network molecules
When tannins polymerise, how does it affect the flavor?
Causes them to become less bitter.
What happens to anthocyanin during ripening? What factors encourage this?
- Anthocyanins increase during the ripening stage
- Plentiful sunlight
- Temperatures between ~ 15°C and 25°C
What 4 factors determine length of ripening?
- Grape Variety
- Climactic Conditions
- Management of the Vine & Vineyard
- Time of Harvest
Name 2 early ripening grape varieties. Name 2 late ripening grape varieties.
- Chardonnay and Pinot Noir are examples of early ripening grape varieties.
- Cabernet Sauvignon and Grenache are late ripening varieties.
Explain the development of sugar as the grapes are ripening
Sugar accumulation in the grape is related to photosynthesis & transpiration
Photosynthesis takes place between 18 - 33 deg C and needs >1/3 full sun.
HIgh sugar accum:
Warm/dry = rapid transpiration = rapid accum of sugar while acid falls, and before flavours/tannins ripen
Risk if extremely hot/water stress photosynthesis slows down.
Low Sugar accum:
Cool/cloudy = slow transpiration = slow accum of sugar and acids remain higher.
Name 3 vineyard management techniques that can slow down ripening.
- Heavy crop loads
- Excessive shading within the vine canopy
- Shoots that are still actively growing
What happens if ripe grapes are left on the vine?
- Grapes start to shrivel
- No more sugar or water are imported to the grape by the phloem at this stage, but water loss in the grape through grape transpiration means that sugars are concentrated.
- Extra-ripe aromas can also develop in this stage
What are the factors that determine ripeness?
- Amount of sugar in the grapes
- Flavor Profile
- Tannin Ripeness
Explain the development of aroma and flavour compounds and pre-cursors during ripening (don’t forget to mention climate)
- with sufficient sunshine methoxypyrazine levels fall
- flavour/aroma compounds like terpenes increase
- the synthesis, retention and degradation of aroma/flavour compounds is influenced by heat and light:
cooler climates - green / citrus
warmer climates - stone / tropical fruit
warmest climates - jamminess
In general “warmer = riper”
Describe tannins during grape formation? During ripening? During winemaking and maturing?
- During grape formation, skin tannins accumulate but are bitter to taste.
- During ripening, tannins polymerise and become less bitter.
- During winemaking and maturation, the tannin compounds that are extracted from the grapes react with other compounds and as part of this their expression may change:
- wines with res sugar tannins are masked (seem softer)
- wines which are dry - tannins may seem more astringent
What is a winemaker’s main concern with tannins?
- Avoid bitter unripe tannins
Why do wines from warm climates tend to have higher levels of alcohol?
The desired sugar ripeness is reached and the grape has high levels of sugar
What can winemakers do if the optimal balance of sugar, acid and tannins isn’t achieved naturally?
Make adjustments to the wine
What’s easiest to adjust: sugar, alcohol, acid, or tannin levels? What does this mean when grape growers try to find optimal ripeness?
- Sugar, alcohol, acid is easier to adjust than bitter, unripe tannins
- Many grape growers will focus on attaining the desired level of tannin and aroma ripeness first since they can adjust the other things
What happens to the vines in late summer? In autumn?
Late Summer
- Cane Formation: green shoots lignify (become woody and rigid)
Autumn
- Leaves fall
- Carbohydrate reserves stored in the roots, trunk, branches
- Vine enters its dormant period
