Pre-fermentation cold maceration
©Copyright Ben Rotter 2006-2008
A pre-fermentation cold maceration (or "cold soak") involves the aqueous extraction, as opposed to the alcoholic extraction, of compounds from the fruit flesh/pulp/skins/seeds into the must. Wines made in this way are commonly perceived as more fruit-forward and complex, with increased aromatic and colour intensity.
2 Fruit type
2.1 Red grapes
Since red wines, by definition, are those which undergo maceration, the significance of pre-fermentation cold maceration in red winemaking is in its focus on non-alcoholic aqueous extraction. This usually means the desire to increase colour intensity/hue and produce wines with softer astringency (particularly in varieties with low colour and phenolics; Pinot Noir for example).
2.2 White grapes
White wines tend to be made with less phenolic intensity than reds. Nevertheless, some white wines, particularly those made from more aromatic grapes, benefit from a limited cold maceration. This allows for the diffusion of fruity aromas and aroma precursors from the grape skins, as well as the extraction of some desirable phenolics, and contributes to the body and ageing potential of the wine. It may simultaneously extract less desirable herbaceous, bitter and astringent compounds. A balanced extraction between adequate aromatics and suitable herbaceous/bitter/astringent compounds can be obtained by controlling maceration temperature and time. It is preferable to keep the maceration temperature below 15°C and typically at 10-15°C. Maceration times in white winemaking may vary from a few hours to around 24 hrs.
2.3 Non-grape fruits
In non-grape fruit winemaking the significance of cold maceration lies in the influence of skin and seed contact for the specific fruit in question. Peaches, for example, possess rather thin skins. (Maceration of peach stones has minimal effect on musts and these are typically discarded for practical reasons anyway.) Whilst the skins do contain some acid, phenolics, etc, their contribution to the must may be of limited influence, and even of limited desirability. The use of cold maceration then turns to the influence the peach flesh has on flavour. The peaches might be processed to extract juice just as white grapes are, but the fruit may instead be crushed and macerated on the flesh pulp. This practice can certainly affect must and wine flavour – wines made without maceration may show lower aromatic intensity and more “higher ester” aromas, whilst wines made from macerated musts may show more “fleshy” characters. Fruits which contain seeds, and fruits whose skins contain significant colour, phenolic or aromatic compounds may also be cold macerated with potentially significant effects on the must. In such cases the advice which applies to both red and white grapes should be of relevance.
3 Temperature and time
Cold maceration is typically conducted at temperatures of about 4-15°C (39-50°F) for 2-7 days, though some winemakers extend this to the more unusual length of 10 days (or even up to 14 days in some more unusual cases). Maintaining the low temperature is primarily to reduce the risk posed by spoilage organisms (for example, heterofermentative lactic acid bacteria, Acetobacter, Brettanomyces, and potentially Kloeckera/Hanseniaspora).
Álvarez et al. (2006) found no significant difference in polyphenolic or anthocyanin contents between 4 and 8 day length cold macerations on Monastrell (a.k.a. Mourvèdre and Mataro) red wine grapes. The results of Canals et al. (2005) show that total phenolic compounds began to level after 5 days and that total anthocyanins remained constant after roughly 3 days of maceration. These findings suggest that maximum phenolic extraction is obtained after 2-5 days of maceration.
Salinas et al. (2005) compared the impact of cold maceration at 5, 10 and 15°C for 8 hours with a control wine macerated at 16°C for 2 hrs on Monastrell grapes. The 15°C maceration resulted in the highest colour intensity, anthocyanin and terpenols concentrations. Wines macerated at 5°C showed the highest ester content. Decreasing maceration temperatures resulted in lower anthocyanin content, slightly lower total polyphenol indices, and decreased tannin (tannic acid). Terpenols continued to be released after 6 months in bottle (although they were never above threshold). It might therefore be assumed that lower maceration temperatures result in increased aromatics, weaker colour and lower phenolic content. Again, however, exceptions exist. Álvarez et al. (2006), for example, found that whilst the concentrations of some aromatic compounds showed higher concentrations at lower cold maceration temperatures, there was generally no difference in volatile compounds concentrations due to temperature.
Clearly, generalisations cannot be made. The influence of maceration temperature and time appears dependent on fruit type and variety, fruit maturtiy, and possibly maceration set-up (see Section 9 for more). It is therefore important that individual winemakers determine the optimum cold maceration regimes for their own fruit, style and set-up.
4 Sensory impacts of CM
Cold maceration is considered to:
increase fruit flavour/aroma (Álvarez et al., 2006; García-Romero et al., 1999; Parenti et al., 2004; Sánchez Palomo et al., 2006), particularly the terpene concentrations in white musts (Baumes et al., 1989);
increase aromatic intensity/complexity (Heatherbell, 1994);
increase mouthfeel/palate fullness - likely due to increased phenol and polysacharrides concentrations (Watson et al., 1994; Durbourdieu et al., 1986);
increase colour intensity and/or hue (Parenti et al., 2004; Durbourdieu et al., 1986);
generally produce wines with softer astringency and increased bitterness.
4.2 Aromatic profiles
Wines made using cold maceration are generally considered to possess more fruit-forward aromatics. Some winemakers, however, consider that the technique can add considerable aromatic complexity that would not be considered fruity in profile. For example, Heatherbell (1994) cold macerated Pinot Noir wines and reported reduced red berry (raspberry, cherry) and increased dark berry (blackberry) fruit character, and increased wood/tobacco/mushroom-earth/blackpepper flavours. Additionally, the results of Watson et al. (1994) noted that pre-fermentation macerated wines were more vegetal.
4.3 TA & pH
Further, cold maceration may result in decreased TA and increased pH in grape musts (Durbourdieu et al., 1986). This is likely due to the liberation of potassium ions from the grape skins. In non-grape musts, the TA often increases (with a corresponding pH drop) with cold maceration. This is likely due to increased liberation of acid from the fruit skins/pulp. Therefore, winemakers conducting cold maceration should bear in mind the pH change and make the necessary allowance for this with their must adjustments, winemaking techniques and stylistic aims.
4.4 Durability of CM’s sensory influence
Some studies have found that whilst differences exist in the colour and phenolic content of musts that have undergone cold maceration, the differences are not maintained in the wine (for e.g., Durbourdieu et al., 1986). Other studies show that certain differences remain in the wine at 6 months after bottling (for e.g., Salinas, 2005).
5 Sulphur dioxide
Sulphur dioxide is sometimes, but not always, added to musts undergoing cold maceration. Typical levels employed are in the range 30-150 mg/l. The addition acts as a microbial inhibitor, but additionally acts as a phenolic solvent by breaking down cell walls and binding with phenolics (Heatherbell et al., 1994; Parley, 1997). Because the presence of SO2 in the must may contribute significantly to phenolic extraction, it is sometimes not added to white grape musts undergoing cold maceration. In such cases, CO2 blanketing is often used instead for oxidative protection.
6 Influence of wild yeast and lactic acid bacteria
Some winemakers theorise that wild yeast and bacteria such as heterofermentative lactic acid bacteria, Acetobacter, Brettanomyces, and Kloeckera/Hanseniaspora remain significantly active in musts during cold maceration. In doing so, they may secrete enzymes which interact with fruit precursor compounds and consequently produce aromatic compounds contributing to wine complexity (Charoenchai, et al., 1997).
7 Fruit maturity
Álvarez et al. (2006) found that the total polyphenolic compounds concentration increased with cold maceration, and was intensified by the use of lower maturity fruit. Conversely, Canals et al. (2005) reported that hot (28°C) maceration of Tempranillo grapes of lower ripeness extracted lower levels of total anthocyanins and total phenolic compounds.
Despite discrepancies in the literature, it is generally advisable that fruit of substantial maturity, uniform ripeness and in healthy condition be used if this technique is to be performed.
8 Ageing potential
Cold maceration is sometimes criticised in the belief that its use results in wines with reduced ageing potential. However, whilst the technique (used with SO2) tends to reduce polymerisation in young wines, after around 2 years it has been shown that no significant difference in anthocyanin content or chemical age index exists between cold macerated wines and control wines (Heatherbell, 1994). Though this single case is far from convincing as a generic argument, it does indicate that this criticism is unjustified.
9 Inconsistent results
The literature contains a number of contradictory accounts concerning the impact of cold maceration on wines.
Girard et al. (2001) found no significant difference in the sensory qualities between 15°C cold macerated Pinot Noir wine and the equivalent control wine. However, Couasnon (1999) found 50% increased extraction of tannins and anthocyanins from Merlot and Cabernet grapes using dry ice (solid CO2) at a temperature of 4°C for ten days. Cuénat (1998) also found increased tannic extraction due to cold maceration, but no significant difference in anthocyanin content. Feuillat (1997) found a significant increase in extraction and chemical parameters from cold maceration at 10-15°C on Pinot Noir grapes. Álvarez et al. (2006) found increased polyphenolic content and aromatic content, slightly decreased colour hue and slightly increased anthocyanin concentrations in Monastrell (a.k.a. Mourvèdre and Mataro) grape cold macerated wines. Parenti et al. (2004) found increased colour hue and generally increased colour intensity, increased flavour intensity, complexity, tannins, and perceived balance in Sangiovese grape cold macerations at 0 and 5°C. Cold maceration with dry ice (solid CO2) resulted in increased total polyphenol, flavonoid and anthocyanidin extraction as maceration temperature decreased, however this relationship did not hold for liquid N2 macerations at the same temperature. In some studies on white grape musts, 12 hour skin contact resulted in musts with excessive phenolic extraction (Ough, 1969; Ough and Berg, 1971; Singleton et al., 1975), whilst in others a positive result was obtained without excessive bitterness or extraction - 16 hours was determined the best in one study on Chardonnay (Arnold and Noble, 1979).
It is clear that the specific effects of cold maceration on musts depend on fruit variety, vintage, maceration temperature and maceration contact time. Differences in these parameters may result in completely different effects. However, in general it may be concluded that cold maceration tends to increase phenolic content, aromatic content and the presence of aroma precursors, colour intensity, anthocyanin content and tannic intensity.
Given the variability in the observed effects of cold maceration, it is advisable to taste the cold macerating juice frequently. Taste comparisons between present-time macerating samples and previously drawn samples will assist the winemaker in determining the most appropriate maceration cessation point. A tasting frequency of every 2 hours (for whites) and every 8 hours (for reds) is recommended.
Cold maceration is preferably conducted in an anaerobic environment to avoid oxidation of the must, particularly in the case of aromatic white wines.
The use of SO2 is a decision which should be based on consideration of both the biological stability of the must and the enhanced phenolic extraction induced by SO2 use.
A cap will typically form during cold maceration. In the case of red winemaking, the cap is typically punched down and stirred into the must once or twice per day to keep it wet and ensure even mixing (of colour and juice, which tend to separate). However, in white winemaking punching down may not be conducted depending on the intensity of phenolic extraction desired.
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Canals, R. Llaudy, M. C., Valls, J., Canals, J. M. and Zamora, F. 2005. Influence of Ethanol Concentration on the Extraction of Color and Phenolic Compounds from the Skin and Seeds of Tempranillo Grapes at Different Stages of Ripening. Journal Agricultural Food and Chemistry, 53, 4019-4025.
Charoenchai, C., Fleet, G.H., Henschke, P.A. & Todd, B.E.N. 1997. Screening of Non-Saccharomyces Wine Yeast for the Presence of Extracellular Hydrolytic Enzymes. Australian Journal of Grape and Wine Research, 3, 2-8.
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Parenti, A., Spugnoli, P., Calamai, L., Ferrari, S., Gori, C. 2004. Effects of cold maceration on red wine quality from Tuscan Sangiovese grape. European Food Research and Technology, 218, 4, 360-366.
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Salinas, M.R., Garijo, J., Pardo, F., Zalacain, A. and Alonso, G.L. 2005. Influence of prefermentative maceration temperature on the colour and the phenolic and volatile composition of rosé wines. Alonso. Journal of the Science of Food and Agriculture, 85, 1527–1536.
Sánchez Palomo, E., Pérez-Coello, M.S., Díaz-Maroto, M.C., González Viñas, M.A. and Cabezudo, M.D.. 2006. Contribution of free and glycosidically-bound volatile compounds to the aroma of muscat ‘‘a petit grains’’ wines and effect of skin contact. Food Chemistry 95, 279–289.
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