Before the start of the grape-harvesting time one must define the quantity of the vintage in regard to making technological and technical decisions in the grape processing factory. This affects the organization of the grape-harvest, its duration and the stages of the grapes’ entering the particular factory. Throughout the maturing period of the grapes, samples are periodically taken so that one can determine the stage of physiological and technological maturation has come, as at that time the harvest must be scheduled. Apart from the technological maturation, the grape-harvest also depends on the climatic conditions that affect the state of the grapes. It is possible, for instance, that a great quantity of rainfall can crack the grape seeds, which leads to a rotten harvest, because of which one must carry it out earlier. A hot and dry climate accompanied by wind is the other negative extreme for grapes, which is unfavorable for their quality. In this case, that can lead to the grapes being dried out, where the seeds become hard, rugged and a considerable part of their aromatic substances are lost.
The grape must’s yield is decreased, and proportionally the quality of the produced wines’ also falls.
The grape-harvest’s duration depends on the volume of the vintage and the climatic conditions for each specific grape type. If a sort of grapes reaches its technological maturity at the same time for the whole vintage, a once-only mass grape-harvest is carried out, while in the case of unequal maturity a partial, continuous grape-harvest is done, where the bunches that have matured properly are picked. The picking process itself can be carried out manually, or mechanically – by grape harvesting machines. Manual picking is characterized by labor expensiveness and engaging a considerable amount of workers for a certain period of time, however, despite this, high quality sorting can be achieved and hurting or damaging the grape seeds and the vine is avoided, unlike in the process of harvesting using grape harvesting machinery. This is a considerable prerequisite for the production of quality wines. The actual technological process passes through the following exemplary stages:
Reception and assessment of grapes
This is a technological operation which is directed towards proving the wine’s origin, as there is a judicial restriction under which 1 kg of grapes must be the bi-product of a maximum amount of 0,7 dm3 of wine. This is carried out in a specialized centre within the wine cellar. In the process of receiving and assessing the following indicators are taken into account:
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Grape type
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Grape mass
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Determining the sugar content and titratable acidity
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Content of dross in the grapes
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Mechanical state of the grapes
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Mechanical content of the grapes
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Sanitary state of the grapes
Grape cooling
The high temperature of the grapes coming into the cellar supposes the quick development of the harmful micro flora, accelerated fermentation as well as high enzyme activity of the enzyme systems present in the grapes, which, on the other hand, supposes really fast and easy must oxidization during processing. At an equal rate of insemination of the grapes with the harmful micro flora, the temperature plays a considerable role in the required time for their doubling. This directly reflects the quality of the wine.
All chemical and biochemical processes are also accelerated under the high temperature, which causes an uncontrollable course of action for the extracting processes and in any case the result is super extraction of phenolic compounds with all the following negative consequences regarding the color, aroma and taste of the wine-to-be. Lowering the temperature is a good precondition for the management of all of these processes.
Cold air cooling is the most frequently used method.
Grape sorting
This operation is obligatory when producing high quality wines for aging, and particularly meant for realization as supererogatory, special reserves, special selections and collectibles.
Sorting is carried out manually on special inspectional belts, and all external dross and injured clusters are removed.
Removing from the clusters and mashing grapes
Taking the cluster apart is a technological operation which consists of separating grapes from their clusters so that the latter cannot take part in the mass-exchange processes with the must and worsen the future wine’s quality. This, however, is not an obligatory white wine-making operation. What is more, the clusters create an additional draining layer which facilitates the must’s getting separated from the solid parts. It is absolutely imperative for processing potentially aromatic sorts of grapes, to separate the grapes from their clusters, so that the clusters cannot take any part in the extracting processes, because that would rigidify the grape must.
Mashing is a technological operation that has the basic task of providing a free fluid phase, which turns into wine by way of alcoholic fermentation. This operation is carried out by mechanically affecting the grapes, causing their grains to get crushed, partially tearing the membranes and destroying the cellular structure of the pulp, yet keeping the entirety of the seeds. The latter is ensured by the additional polymer coating on the rollers of the grape grinder and the precise regulation of the distance between them. Mashing can come before or after the clusters’ division.
