Vitis 40 (1), 3942 (2001) Influence of oxygen supply on the susceptibility of cv. Palomino fino must to browning R. CASTRO and C. G. BARROSO Analytical Chemistry Department, Faculty of Sciences, University of Cádiz, Puerto Real, Cádiz, Spain Correspondence to: Dr. R. CASTRO, Analytical Chemistry Department, Faculty of Sciences, University of Cádiz, P.O. Box 40, E-11510 Pol. Rio San Pedro, Puerto Real, Cádiz, Spain. Fax: +34-5601 6288. E-mail: remedios.castro@uca.es Summary Experiments have been conducted on the oxidation of must (cv. Palomino fino). At the initial decanting process prior to fermentation, wines produced from hyperoxidized must had a reduced content of oxidable polyphenolic com- pounds and a reduced tendency to browning; they main- tained these characteristics after bottling. Intermediate doses and the combined use of oxygen and sulphur dioxide were not fully effective in resolving the problem of brown- ing for must of this grape variety. The larger the dose of oxygen (30 mg·l -1 ), the less the content of hydroxycinnamic esters and the lower the oxidizability. This dose was appro- priate for producing a "fino" sherry wine with a low ten- dency to browning, retaining the sensory characteristics of this particular type of wine. K e y w o r d s : must oxidation, Palomino fino, Sherry wine, browning, polyphenols. Introduction The typical "fino" Sherry wines of the Jerez region in Spain are submitted to a system of dynamic biological age- ing (CASAS 1985) under a surface layer of yeasts ("veil of flor"). This protects them from environmental oxygen and significantly influences their organoleptic properties. After approximately two years of biological ageing, the wine is prepared for bottling and is no longer protected from oxygen; hence, browning problems occur, as with other white wines. SINGLETON (1987) and MACHEIX et al. (1991) have shown that the deterioration of the organoleptic and sen- sory properties caused by the phenomenon of browning is due to the oxidation of polyphenolic compounds. As for other white wines, a variety of techniques has been devel- oped to stop this evolution, e.g. bottling under an inert gas atmosphere (PRASS and VIRGO 1976; GAI 1989), and the use of particular fining agents (BARON et al. 1998). For some years, a technique known as "must hyper- oxidation" has been used (SCHNEIDER 1998): By providing oxygen, some of the polyphenolic compounds are oxidized into polymers of low solubility which can be easily elimi- nated. This leads to a wine with a lower content in oxidable polyphenolic compounds, assumed to have a lowered ten- dency to browning. This enotechnical procedure has previ- ously been employed to produce young white wines with good organoleptic characteristics and a higher resistance to browning (GUERZONI et al. 1981; CHEYNIER et al. 1991; NICOLINI 1992). The capacity for oxygen consumption by must is highly variable and depends on the initial content of hydroxycinnamic acids, a group of polyphenols which dif- fers depending on the grape variety (SCHNEIDER 1998). In this paper, we studied the effect of hyperoxidation of must (cv. Palomino fino) with the aim to produce a "fino" Sherry wine which is resistant to browning and retains its sensory characteristics. Material and Methods J u i c e s : In 1996 and 1997 clusters (Palomino fino) were pressed (<1.5 kg·cm -2 pneumatic press) and calcium carbonate (2 g·l -1 ) and tartaric acid (pH 3.25) were added. P r o c e s s o f h y p e r o x i d a t i o n : For each harvest two trials were conducted in containers (30 l). In each trial, 5 vessels were used. In the hyperoxidized musts, oxygen was supplied before decanting by means of a diffuser, with- out prior addition of sulphur dioxide. The doses are as fol- lows: A = 10 mg O 2 ·l -1 must; B = 30 mg·l -1 ; C = 30 mg·l -1 followed by 100 mg·l -1 SO 2 1 h after addition of oxygen; D = SO 2 after decanting; E = control, with sulphur dioxide at the onset of conventional vinification. Oxygen diffused into the must was measured by an oxymeter (Cark electrode, Oxi-92, Crison Instrument, Barcelona, Spain). One hour later liquid gelatine (0.05 ml·l -1 , Gelsol TM , AEB Ibérica, Barcelona, Spain) and silica sol (0.5 ml·l -1 , Baykisol TM , AEB Ibérica, Barcelona, Spain) were added to each vessel as fining agents. All musts were decanted after 12 h. Before fermentation SO 2 (100 mg·l -1 ) was added to musts A, B and D. After fermentation (7 days at 25 ºC) and the analysis of the polyphenols and enological parameters, wines that had received the same dose were combined and kept in a vessel until it was racked off the lees. Thereafter, the wine was fortified to 15 % v.v. and then underwent the biological ageing process under yeasts ( "veil of flor"). P o l y p h e n o l i c p r o f i l e : 80 ml of filtered wine (0.45 mm) was analysed, in triplicate, by HPLC. Mobile phases employed were: solvent A (95 % water, 5 % methanol) and B (95 % methanol, 5 % water) at pH 2.5 (super-pure sulphu- ric acid). Elution phases: gradient elution from 100 to 85 % solvent A (5 min), gradient elution from 85 to 50 % solvent A