Destemming: precision, quality, innovation with Bucher Vaslin
Destemming is a practice that varies greatly depending on the time and region. Its importance varies depending on the grape variety, the type of wine sought (primeur or ageing wine), and the health of the grapes.
Total destemming and partial destemming
Destemming can be total or partial depending on traditions, grape varieties, and the vintage. In total destemming, all the stalks are removed and only the berries are retained. In partial destemming, only a portion of the harvest is destemmed.
The choice to carry out partial destemming may be motivated by the search for sweetness, as evidenced by the latest work carried out by Marie Le Scanff and Axel Marchal. The work funded by the Denis Dubourdieu Chair, of which Bucher Vaslin is a patron, has shown that the stems can provide a sweet-tasting phenolic compound: astilbin. Depending on the grape varieties and the vinification method, the fraction of sweet compounds provided by the stems can vary. It is up to the winemaker and oenologist to establish the level of destemming, because the stems can also release bitter and astringent compounds, but also provide vegetal nuances.
Destemming in red winemaking
Destemming is an important step in the vinification of red wines, as it influences both the quality and the sensory profile of the resulting wines.
Firstly, destemming helps to reduce the volume of the vat room occupied by the harvest , as the stalks constitute a significant part of the bunch. It also helps to limit the expression of herbaceous characteristics , often undesirable, that the stalks can release, particularly if their phenolic maturity is not optimal. Destemming therefore helps to obtain more supple, rounder wines without overly pronounced vegetal notes.
This process can, however, have some drawbacks. In the absence of stalks, the cap of marc formed during fermentation is more compact, which can complicate pumping over operations and limit extraction. In addition, the stalk sometimes plays a protective role against oxidative casse thanks to the substances it contains.
Destemming in white wine vinification
In the case of white winemaking , the question of destemming arises differently. While the operation can be carried out, it does have certain technical drawbacks, particularly during pressing. Indeed, the absence of stalks makes the "mass filter" formed in the press more compact and therefore more easily clogged, which reduces the efficiency of juice drainage and slows down pressing. The stalks, by their structure, naturally act as drains, thus facilitating the flow of the musts.
It should also be remembered that, in the production of white wines, the press's primary role is not to break the skin of the berries on a previously destemmed harvest: this step is carried out upstream by crushing, an essential operation allowing the juices to be released and the gentle extraction of aromatic compounds to begin. The press must then ensure the gradual separation of the juices, without excessive crushing which would bring in undesirable compounds.
The 3 ways of separating the berry and its pedicel
There are three main ways of separating the berry from its pedicel.
The first mode is based on tearing , where the rupture occurs directly by mechanical traction.
The second method consists of rolling the bunch , which aims to reduce the binding force between the berry and its pedicel. This mechanism is particularly suited to grape varieties whose binding force, in the radial axis, remains relatively weak, as is the case for Pinot Noir.
The third method is separation by inertia : the berry is subjected to an acceleration that artificially increases its weight, then the bunch is abruptly stopped on an openwork surface. The force exerted is then applied along the axis of the pedicel, which facilitates detachment. This method of separation is very effective for grape varieties with thick skins such as Cabernet-Sauvignon.
Keen to cover all of these separation methods, Bucher Vaslin offers two destemmer technologies within its Delta range.
The Delta Evolution destemmers with rotating cage can destemmer in three separation modes with more or less significant portions depending on the configuration of the cage, the shaft and the speed ratios.
Delta Oscillys destemmers with rectangular cage, without beater, shaft or rotating cage which separate the berry from its pedicel solely by inertia.
Rotating cage destemmers
Delta Evolution destemmers are now a versatile technology, allowing, depending on their configuration, all three berry separation modes to be used. The design of the machine, including the length and position of the central shaft fingers and the position of the feed deflectors, determine the predominant separation mode and the overall destemmer efficiency.
With mechanical harvesting
In the case of mechanical harvesting, characterized by a high percentage of already destemmed berries, a low presence of partially destemmed bunches but also a significant proportion of plant debris, it is preferable to use a destemmer with a rotating cage equipped with a long-finger shaft . This configuration in fact favors separation by tearing in the lower part of the cage and by inertia in the upper part of the cage.
The long fingers , in addition to facilitating continuous cleaning of the cage thanks to a reduced distance between it and the tree, have a specific design: they are equipped with a flattened tip covered with a rubber termination, thus avoiding crushing of the berries . Their particular positioning helps to maintain a regular progress of the harvest in the cage while ensuring effective unclogging , thus limiting flow interruptions and improving the regularity of the treatment.
The cage perforations depend on the grape variety and the average size of the berries : too large a diameter risks letting fragments of stems through, while too small a diameter can increase the crushing rate and slow down the flow rate. The interchangeable cages (Ø15/18, Ø15/22, Ø22, Ø25 or Ø32) thus offer flexibility of use, allowing the device to be adjusted to different batches of harvest.
Attention is paid to the profile of the perforations – rounded on the internal face for stainless steel, rounded internal and external for HDPE cages – helps to preserve the integrity of the bays by limiting crushing.
The rotation speed of the cage is adjustable depending on the flow rate, it must be adjusted to ensure a constant flow rate.
With manual harvesting
In the case of manual harvesting, a destemmer with a rotating cage and a short shaft is preferred in order to promote separation by rolling and inertia.
The configuration, combining a cage with a deflector and a shaft without a deflector, allows for gentler treatment by reducing the speed at the destemmer's entrance . It is therefore particularly suitable for grape varieties with fragile skins. On the other hand, the treatment flow rate is reduced, which reserves this technology for installations prioritizing oenological quality over productivity. This solution is exclusive to Bucher Vaslin and is the subject of an international patent.
For example, for a Delta Evolution 2 or 4 destemmer, the rate of whole berries on Pinot Noir can increase from 25% to 75%, demonstrating the direct impact of the machine's design on preserving the integrity of the berries . This performance is consistently found on other grape varieties such as Syrah, Cabernet, Gamay and Riesling, attesting to the versatility of this technology.
Delta Evolution destemmers feature built-in automatic rinsing and a design that limits retention areas, making cleaning easier, improving hygiene and reducing the risk of contamination while ensuring simple and efficient use in every winemaking cycle.
Stemmers with virtual pivot point
The Delta Oscillys inertia destemmers represent a significant technological breakthrough compared to traditional destemmers. Bucher Vaslin has managed to break away from the initial system where the cage was on a fixed pivot point by patenting a new virtual pivot point device . The fixed pivot has the disadvantage of too little movement at the start of the cage to ensure separation of the berry from its pedicel.
With Bucher Vaslin's virtual pivot, destemming is implemented as soon as the bunch is introduced into the cage. The rectangular cage, animated by an up-and-down movement with its virtual point, provides a more uniform separation force during the bunch's journey through the destemmer.
The rectangular HDPE cage design allows for single-layer processing of clusters , ensuring much more uniform processing. The large opening area also provides high tolerance to flow rate variations.
Optimising the cage movement ensures that each beat is used efficiently, thus reducing the total number of stresses required for destemming. The bunch is therefore destemmed with fewer beats, which results in increased preservation of the berries , accompanied by a significant reduction in free juice . Finally, since the stalks and green debris do not undergo significant mechanical degradation, they retain a structural integrity that facilitates their separation during sorting.
Technical characteristics
Oscillys XM:
Up to 15 T/h on whole harvest
Large hexagonal section cage, 28 mm hole diameter
Electric calibration roller gap adjustment from 15 to 19 mm (option 17 to 21 mm)
Optional distribution roller spacing adjustment with drip box.
Oscillation speed adjustment from 250 to 450 movements/min
Speed adjustment for roller rotation
Oscillys Max option to reach 22 T/h on mechanical harvesting
Oscillys XL:
Up to 25 T/h on whole harvest
Large hexagonal section cage, 28 mm hole diameter
Electric calibration roller gap adjustment from 15 to 19 mm (option 19 to 23 mm)
Oscillation speed adjustment from 250 to 450 movements/min
Speed adjustment for roller rotation
Oscillys Max option to reach 40 T/h on mechanical harvesting
Bucher Vaslin now offers two complementary destemming technologies, incorporating the latest design advances. These innovations result in improved separation efficiency, a reduction in the mechanical energy applied to the bunches (expressed in W/kg of grapes), a significant reduction in the production of free juice, as well as a reduction in noise pollution and increased cleanliness of the processed harvest.
These developments place this equipment at the service of winemaking that is more respectful of the raw material and the quality objectives of producers.
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