Two Stages of Grape Berry Development

Our friend has been helping us with our vineyard work. Recently, we showed him the Chardonnay fruitset 2 weeks after bloom. He was surprised at how large they were and so was I. He said that at this rate, the grape bunch will be huge.

Grapes, however undergo a lag phase between two growth phases. Sneaky berries!
Here is a chart showing all that is going on once berries are set. The chart illustrates the double sigmoidal curve of berry growth and development:¹

Development During First Growth Period2

Development During Second Growth Period

The first period of growth lasts approximately 60 days past bloom The berry is formed and the seed embryos are produced Rapid cell division in the pericarp occurs through the first few weeks, establishing the total number of cells within the berry The berry expands in volume as solutes such as tartaric and malic acid accumulate Tartaric acid appears to accumulate during the initial stages of berry development, and malic acid accumulates just prior to véraison Hydroxycinnamic acid also accumulates during the initial period of growth Tannins including the monomeric catechins also accumulate during the first period of growth Minerals, amino acids, micronutrients, and aroma compounds (such as methoxypyrazines have all been observed during the first period of berry growth

The first growth period is followed by a lag phase during which little or no growth occurs. The second growth phase coincides with the onset of ripening (veraison) Cells in the pericarp undergo expansion The berry expands in size due to the influx of water, carbon and mineral nutrients Softening and coloring of the berry occurs during ripening Synthesis and accumulation of anthocyanins occur during ripening There is an increase in abscisic acid (ABA), sugar levels and color development The big change during the second growth period is the accumulation of glucose and fructose as the grape shifts into ripening mode Important aroma and flavor compounds are produced late in fruit ripening The berry approximately doubles in size between the start of ripening and harvest

It is important to understand the development of the grape berry because knowing when flowering occurs, the lag phase can be predicted. In our case, if flowering occurred during late June, our lag phase will be toward the end of August. Our nets should be up by that time to prevent the birds from eating the fruits of our labor!

References:
1. Moschou, Panagiotis & Aziz, Aziz & Roubelakis-Angelakis, Kalliopi, Chapter 7, Polyamines and grape berry development, The Biochemistry of the Grape Berry, (2012), 137-159.
2. James Kennedy, Understanding Grape Berry Development, Practical Winery and Vineyard Journal, July/August 2002.