Determination of the grape harvesting period
Controlling the grape ripening process is crucial in order to determine when to harvest, depending on the wine that has to be or can be obtained. At the end of the veraison (when grapes pass from the herbaceous to the ripening stage, with yellow or red skin colour) it is best to perform two inspections per week to determine a number of important factors of the ripening process. Take a sample using bunches or grapes taken from the same vine or the same area of the vineyard. Now crush the grape sample and, using a saccharimeter or a refractometer, determine:
1) Sugar content.
2) Total acidity and Ph.
Light white wines
Harvest the grapes before they are fully ripe.
Total acidity above 7 g/litre
Sugar content below 17° Babo.
Structured white wines
Wait for the grapes to fully ripen.
Total acidity between 5 and 6 g/litre
Sugar content above 20°
Babo Light red wines
Harvest the grapes before they fully ripen.
Total acidity above 6.5 g/litre
Sugar content below 18° Babo.
Aged red wines
Wait for the grapes to fully ripen.
Total acidity above 5 g/litre
Very low acidity and high Ph in red wines can cause fermentation problems.
Wine-making products or vinification
Products used during vinification to prevent alterations in the must by selecting fermentation yeasts and speeding up the decantation and extraction processes.
Sulphur dioxide and its derivatives:
useful for selecting the yeasts and favouring those with the best fermentation characteristics
- prevents bacterial alterations when vinifying bad grapes
- avoids undesired oxidisation of must in the early stages
- ensures regular fermentation
- enhances the varietal characteristics of the grapes
Pectolytic enzymes for white musts
- these separate the clear part of the must from the solid part (sediment)
Enzymes for red musts
- these extract the colour from the grape skins
- they represent the source of nourishment for the yeasts
- They stabilise the colour of red wines
- They prevent must oxidisation in case of bad grapes.
White vinification of precocious grapes
The white vinification of precocious grapes ( Chardonnay, Pinot, Sauvignon, etc.) is done by the fermentation of the must only without maceration of the solid parts of the grapes.
1) Quickly separate the must from the skins, to prevent tannin extraction
2) During pressing, to exhaust the marc, separate the “flower must” from the last fraction of crushing (“pressed”). The “flower must” represents 60-65% of the weight of the cluster. The potassium metabisulphite can be added before crushing or immediately after. Dosage is between 12 and 16 grams per 100 kg of grapes.
3) Immediately cool the must to a temperature below 18-20°
4) Clarify the “flower must” by separating the solid part consisting of pieces of skin and parts of the pulp which form a deposit (“clarification marc”). For this operation, use white must clarification enzyme in doses of 2-5 grams per hectolitre, dissolving this in a small fraction of must before adding to the mass to be clarified.
5) The next step is fermentation. The choice is between spontaneous fermentation and favouring this process by adding 20-30 grams per hectolitre of selected yeast. Above all, during the early days of fermentation, the fermentation temperature must be kept between 16 and 20°.
6) At the end of fermentation, perform the first transfer operation without adding products containing sulphur dioxide, which can instead, if so desired, be added at the time of the second transfer operation, 5-6 days after the first.