2.5 Grape Development

Question 1

what are aroma precursors?

Answer 1

compounds with no aroma that become aroma compounds during fermentation
ex: methoxypyrazine - herbaceous aroma

Question 2

at what temps does photosynthesis take place at it’s maximum rate?

Answer 2

64-91º F

Question 3

name the four stages of grape ripening

Answer 3

early grape growth
version
ripening
extra-ripening

Question 4

summarize early grape growth

Answer 4

hard, green grapes grow in size - tartaric/malic acid accumulate - aroma compounds/precursors develop - tannins accumulate and are very bitter - sunshine promotes tannin accumulation - sugar levels low and water flow is high

Question 5

summarize verasion

Answer 5

grape growth slows for a few days while grape cell walls become stretchy and supple and chlorophyll in skin cells is broken down and black grapes become red due to synthesis of anthocyanin

Question 6

what happens if too much water and nitrogen are present during early grape growth?

Answer 6

can prolong the stage because nitrogen and water encourage shoot growth over ripening. this can cause a delay in onset of ripening which could mean insufficient time for ripening.

Question 7

describe the effects of mild water stress during early grape growth

Answer 7

can speed up the stage and lead to smaller grapes which have a higher skin to juice ratio. can be a positive for red grapes because they may have higher levels of color, tannins, aroma compounds.

Question 8

very briefly summarize the ripening stage of grape development

Answer 8

cells in grapes expand rapidly, sugar and water levels accumulate, acid levels fall, tannin/color/aroma precursors and compounds develop.

Question 9

During the Ripening Stage of grape development, what is affected in years of cool weather or cloud cover?

Answer 9

rate of photosynthesis drops and may hinder sugar levels

Question 10

The length of ripening stage depends on what factors?

Answer 10

• Grape variety- early/late ripening
• climactic conditions
• managment of the vine and vineyard
• time of harvest

Question 11

What happens in the extra ripening stage?

Answer 11

grapes shrivel. no water or sugar are imposed into the grape. water loss through transpiration concentrates sugars. extra ripe aromas develop, which may or may not be desirable depending on wine style.

Question 12

What is coulure and how does it happen?

Answer 12

• a condition of the grape bunch in which fruit set has failed for a high proportion of flowers. Fertilization is unsuccessful, no grape develops.
• caused by an imbalance in carbohydrates levels. Can result from low rate of photosynthesis which may be caused by cold, cloudy conditions, or hot, arid conditions with high water stress. Can also result from vigorous shoot growth diverting carbohydrates from the inflorescence. Very fertile soils, heavy application of fertilizers, vigorous rootstocks all cause strong shoot growth.

Question 13

What is millerandage and how does it happen?

Answer 13

• a condition in which there is a high proportion of seedless grapes. Seedless grapes can still ripen normally, but are smaller than grapes with seeds. Therefore it can reduce the volume of wine that can be produced. Some seedless grapes stay small, green and unripe which is negative for wine quality.
• can result from cold, wet, windy weather at fruit set.

Question 14

Explain the relationship between sugar accumulation during ripening and climate.

Answer 14

Sugar accumulation within the grape is correlated to the rate of grape transpiration. Grape transpiration and therefore sugar accumulation is faster in warm, dry conditions than in cool, humid conditions.

Question 15

Explain the effect of sunshine on grape pre-verasion and post-verasion

Answer 15

Sunshine on grapes promotes tannin accumulation pre-verasion and greater polymerization post-verasion.

Question 16

Describe the effect of sunshine on anthocyanins during ripening

Answer 16

anthocyanin increase during ripening and increase most rapidly with plentiful sunshine and warm temps