The forecasted volumes per plot or block of plots allow us to optimize workforce requirements and the types of wine-making containers (materials, capacity in hectolitres) necessary for a specific wine style according to the harvest order determined by maturity assessments.
Defining a harvest order is not limited to choosing the harvest dates for the entire vineyard. One must also estimate harvest volumes for each plot and each block, in order to follow this harvest order in the winery and manage vat availability.
Several methods can be used to estimate yields and grape volumes to be harvested. For this, the planting density, the number of bunches per vine, the number of berries per bunch, the weight of the berries and the grape variety must all be taken into account. Missing vines, young vines and mixed vines (Mixed vines) must also be taken into account. The plot grid can be made up of groups of a few dozen vines. The estimates only give a relative idea of the yield and each year several parameters such as weather conditions or the average bunch weight cause these results to vary. The annual weight variation rate is estimated to be between 15 and 50%. The formula used for the calculation is the following:
Yield (kg/ha) = number of vines number of bunches/vine average bunch weight * density
Estimates can be made from véraison onwards, once all thinning operations have been completed. When the estimates have been made, the results obtained in kg or in tons must be converted into harvest volumes, that is to say, hectolitres. It is therefore necessary to calculate the quantity of grapes necessary in kg to make one hectolitre of still wine. To do this, a vinification rate is assigned which will partly depend on the grape variety. This can range from 115 to 140 kg of grapes for 1 hl of still wine. The grape varieties with large berries such as Merlot tend to have a high juice yield (about 115 kg for 1 hl) while grape varieties with small berries such as Cabernet Sauvignon have a lower yield (135 kg/hl).