The berry sugar loading : an indicator of grape quality
What is sugar loading?
The sugar loading of grape berries (evolution of the quantity of sugars per berry), widely described by Pr. Deloire during the last decade, constitutes a physiological marker integrating the functioning of the vine in its environment.
The sugar loading includes two distinct periods:
- A first period of active sugar loading during which the berries are loading sugar: from véraison to the end of the sugar loading
- A second period of plateau during which the sugar quantity per berry is constant. Brix can increase or decrease, by berry volume variation (dilution or concentration)
Figure 1 :Sugar quantity per berry after Veraison
Four relevant parameters can be extracted from the sugar loading curve:
- the rate of loading during the first phase (in mg/berry/day)
- the duration of active sugar loading (= duration of the first period)
- the date of the end of active sugar loading
- the Brix at the end of sugar loading
This last parameter is a relevant indicator of the functioning of the vine and of the “quality” of the ripening of the grapes. Indeed, any factor of imbalance (excessive yield, water stress, heat stress, radiation deficit, excess of vigor, etc …) induces a decrease of the sugar loading into the berries which results in a lower Brix at the end of sugar loading.
Sugar loading and water deficit
One of the most impacting factors on berry sugar loading is the water deficit during ripening as show in the graph below.
Figure 2 : Brix after sugar loading stops
How to measure berry sugar loading?
Measuring the quantity of sugar that loads into the berries can be carried out using the “berry-cup” technique, describe by Wang et al. (2003). The berry-cup system consists of a single peeled grape berry immersed in a buffer solution in a cup. A small cross-incision is made on the stylar of the berry, thus the sugars unloaded from the phloem are transported into the buffer solution and can be analyzed.
A much easier way to analyze sugar loading is to measure the berry volume (mL) and to multiply it by the sugar concentration of the juice (g/L). That calculation gives an estimate of the sugar quantity per berry in mg. Analyzing it once or twice a week allows to build the sugar loading curve that provide a better understanding of the ripening behavior of the grape.
Why measuring sugar loading?
The interpretation of the sugar loading curve provides to vine growers and winemakers a real-time monitoring of grape maturation, at block, vineyard and region scales. The practical uses are:
- qualification of the grape potential
- detection of the loss of berry volume (shriveling)
- block diagnosis: identify blocks with sugar loading issue
- forecasting the harvest date and the grape profile
- harvest planning
- orientation of the winemaking process
Fruition Sciences has partnered with Vivelys and ETS Lab to help you better time your harvest!
With Dyostem analysis, you will monitor berry volume variations along active sugar accumulation from veraison to picking. This key information about ripening dynamic will help you refine your picking decision on top of classically measured fruit parameters. Contact us to learn more about it.
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