After primary fermentation is complete, grape skins, seeds and any stems, can be left in contact with the wine for a length of time before pressing. The technique is referred to as extended post-fermentation maceration and is almost exclusively used in red winemaking. The aim is to increase the extraction of phenolic compounds from the skins, seeds, and any stems, in order to optimise the colour, flavour and tannin structure of the wine. During the 2018 Cabernet trial, extended post-maceration treatments of 21 and 60 days were conducted.
Background
The technique is traditional in many European regions including Burgundy with Pinot Noir, Bordeaux with Cabernet-family varieties, Piedmont with Nebbiolo, and to a lesser extent the Rhone Valley with Shiraz and associated varieties. In Australia the technique is most commonly used with Cabernet Sauvignon, flowed by Shiraz, Merlot and Pinot Noir, and to a much lesser extent with a wide range of other varieties (Joscelyne 2009).
The length of time that skins and seeds are in left contact with the juice or wine, during both fermentation and any period of post-fermentation maceration, is probably the most critical factor in defining phenolic profile and sensory properties of the resulting wine and is also one of the easiest to control (Casassa and Harbertson 2014).
Application and helpful hints
Post-fermentation maceration is best performed in sealed vessels, because if the cap of skins and seeds is exposed to oxygen or to vinegar flies, acetaldehyde, acetic acid and ethyl acetate may be formed. The cap is usually submerged and the container topped-up so that there is no ullage. However, during the first few days the volume of wine can increase or decrease mainly as a result of temperature changes and residual fermentation activity. Therefore, it is important to check the tank regularly and to allow space for any wine expansion during this period.
A fine mist of SO2 solution may be sprayed onto the surface of the wine before the tank is sealed, and this can be repeated periodically during the maceration period in order to discourage the growth of film-forming yeast and acetic acid-producing bacteria.
It is not possible to be prescriptive about the optimal length of maceration, which in the literature can vary from a few days to two months or more. The initial concentration of grape phenolic compounds in the grapes and their extractability, are two key variables, which vary depending on the variety and the season. Previous winemaker experience with the variety and region, as well as recognition of seasonal differences in fruit composition, are important factors in determining the ideal length.
Malolactic fermentation should be initiated during primary fermentation and is invariably complete by the conclusion of post-fermentation maceration.
Practical considerations
Extended post fermentation maceration is usually conducted in the same vessel in which the wine was fermented, meaning that additional fermentation capacity is needed if the technique is adopted. One difficulty is that it is virtually impossible to obtain a representative sample of a wine while it is undergoing extended maceration, because the composition of the wine above the headed-down skins is different from that of the wine in the cap and the wine lower down in the tank. It can therefore be very difficult to determine the level of extraction which has been achieved, based on sensory assessment.
Potential risks
Extended post fermentation maceration can result in large changes in the chemical composition and the sensory characteristics of wine. The most commonly reported risks are the potential development of bitterness and overly astringent tannins, and the possibility of spoilage by undesirable yeast or bacteria.
Consequently, it is advisable to take a cautious approach when trialling the technique, by starting with a small batch and assessing the results over time. Blending trials can also be conducted, to ascertain the proportion of extended-maceration wine required to achieve the desired sensory effects.
Resources
Casassa, L. F., Harbertson, J. F. 2014. Extraction, Evolution, and Sensory Impact of Phenolic Compounds During Red Wine Maceration. Ann. Rev. Food Sci. Technol. 5: 83-109.
Joscelyne, V. L. 2009. Consequences of extended maceration for red wine colour and phenolics. Adelaide, SA: University of Adelaide; 246 p. PhD thesis.
Godden, P. 2018. Extended post-fermentation maceration. Aust. N.Z. Grapegrower Winemaker (658): 70-71.
Godden, P. 2019. Exploring the effects of extended post-fermentation maceration. AWRI Tech. Rev. 238: 6-11.