Maceration anaerobic metabolism

VI. SPECIFIC CHARACTERISTICS OF GRAPE BERRIES IN CARBONIC MACERATION ANAEROBIC METABOLISM... 

Winemaking by carbonic maceration (CM) is a process exploiting the adaptability of intact grape berries to an oxygen-deprived medium enriched with carbon dioxide (C02). This adaptation is reflected almost instantly inside each berry by the transition from a respiratory to fermentative anaerobic metabolism (AM). 

FIGURE 1.1 Scheme of carbonic maceration winemaking. AM, anaerobic metabolism of grape berries YAF, yeast alcoholic fermentation M, maceration qd = pair temperature (q°C) action duration (days). (Figure from CEnologie—fondements scientifi-ques et techniques. Flanzy et al. collection Sciences Techniques Agroalimentaires. Technique Documentation, 1998, p. 780. Reproduced with the permission of the Editor.)... 

The fennentor is filled with whole grapes under a blanket of carbon dioxide and kept at a moderate temperature (20-30°C) for 1-2 weeks. The atmosphere of the fermentor is then saturated with CO2 for 8-15 days. This is the pure carbonic maceration phase. Anaerobic metabolism reactions modify grape composition. Substances from the solid tissue disintegrated by anaerobio-sis are also diffnsed in the juice and the pulp. 

The carbonic maceration aroma is probably due to the successive action of the anaerobic metabolism of berry, yeast and perhaps bacteria, but the mechanisms of these transformations remain to be determined. In 1987, Flanzy et al. again took up this hypothesis. 

In a fermentor undergoing carbonic maceration, the grape berry is transformed by anaerobic metabolism reactions of its own cells. These reactions are independent of any yeast involvement and have been covered in the preceding section. Tissue degradation favors the maceration phenomena involved. Phenolic compounds, anthocyanins, nitrogen compounds and other components of the solid parts of the berry are diffused in the juice of the pulp. 

Different systems can be developed to make use of carbonic maceration. Its success depends on anaerobic metabolism intensity, which itself depends on fruit integrity, degree of anaerobiosis, possible traces of oxygen, duration and temperature. 

The temperature and duration of the anaerobic phase are essential parameters of carbonic maceration. The elevation of the temperature is less important with carbonic maceration than with crushed grapes, which have more active fermentations. In hot climates, this fact was used to the winemaker s advantage, when controlling temperatures was more difficult than today. The anaerobic metabolism, however, must take place at... 

Table 12.20 (Flanzy et al., 1987) compares the composition of traditionally made wines (crushed grapes) and wines having nndergone carbonic maceration (effected at 25 and 35°C). The importance of temperature in anaerobic metabolism is shown. At 35°C, this techniqne permits the same tannic structure as traditional winemaking. In general, density and dry extract, fixed acidity and phenolic compound concentrations are lower with carbonic...

The intermediate steps of metabolism have been the subject of much discussion. Some aspects will be treated briefly below. Meyerhof (54) states that the glucose molecule passes anaerobically through twelve stable intermediary steps before forming alcohol and carbon dioxide at least three dissociable organic enzymes, twenty or more enzyme proteins and some bivalent metals (Mn and Mg) are necessary for the breakdown. This is a widely accepted conclusion from the work on fermentation by yeast extracts (press juice, maceration juice prepared from dried yeast, frozen yeast, or mechanically disrupted yeast) in which phosphoiylation is considered important in desmolysis. Decarboxylation of pyruvic acid appears to be the source of the carbon dioxide. Obviously then, carbon dioxide production is far from the initial step of permeation of glucose. 

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