Winetech Technical Yearbook 2022

NOVEMBER

MODERN AMPHORAE AND OAK BARRELS

MODERN AMPHORAE DIFFER CONSIDERABLY FROM ANCIENT ONES. THEY HAVE SIMILAR OXYGEN TRANSFER RATES AS BARRELS AND ARE CONSEQUENTLY NOT ONLY USED AS FERMENTATION VESSELS, BUT CAN ALSO PLAY A ROLE IN WINE MATURATION.

BY CHARL THERON

A modern amphora.

COLLECTIVE USE OF AMPHORAE AND BARRELS Amphorae need not replace barrels to benefit the wine quality, but the different vessels can complement each other. Barrels are needed to polymerise the tannins of the wine, while the amphorae can improve the retention of fruitiness during maturation. Due to the micro-porosity of amphorae, balanced redox potential is also created in the wine, which leads to a lower sulphite requirement. Due to the different effects of various vessels during maturation, the number of components for blending is increased to create a broader product spectrum for winemakers. Wines matured in wood barrels have a more pronounced tannin profile, and amphorae contribute

MODERN AMPHORAE are already used in traditional French wine regions, but in many other areas are still only used on an experimental scale. Amphorae have high permeability and differ individually regarding their oxygen transfer rate (OTR). This will determine whether a cellar can use them only in the short term or as long term maturation vessels. Adding to this uncertainty, some amphorae suppliers do not know this difference and cannot supply the cellar with OTR values. THE USE OF AMPHORAE INSTEAD OF USED BARRELS If a winemaker prefers to use less new wood, the older barrels need to be adequately treated before use. This may lead to the extraction of undesirable components. By using amphorae

more minerality and elegance. Together these characteristics can add more complexity to wines. Instead of blending the different components after maturation, it can be done sequentially when barrel maturation in new or used oak can be followed by amphorae maturation for a couple of months before bottling. AMPHORAE CHOICES Amphorae differ amongst suppliers giving winemakers a choice depending on their requirements. It can be used for different red and white wines as well as creating oxidative characters in wines. The oxygen requirements of wines differ depending on the cultivar, vinification protocol and maturation period. The OTR of ceramic vessels is determined by the following parameters: • The firing temperature. Increasing firing temperatures decrease the porosity and consequently the OTR. • The temperature gradient during firing and the reliability of equipment used for the firing. • The surface-to-volume ratio of the vessel. The smaller the vessel, the higher the OTR will be. Different ways can be used to express vessels’ oxygen permeability or OTR. Experiments found an OTR decrease from 5 173 500 to 5 952 cm 3 /m 2 /day, indicating the vast difference between traditional amphorae and modern ones. The pore size measurements confirmed this. Amphorae can play an important role in developing wine quality in combination with wood, without necessarily replacing it. REFERENCE https://www.wineland.co.za/modern-amphorae-and-oak barrels/

instead of old barrels, the micro-oxygenation effect of barrels can be sustained without adding unpleasant flavour and taste compounds. The average OTR of oak barrels is 10 mg/L/year. However, the OTR of oak barrels is dynamic and will decrease over time. Contrary to this, the OTR of amphorae can be set when it is produced. THE COMPOSITION OF AMPHORAE Most amphorae used for winemaking are made with terracotta. It is ceramic, mainly consisting of clay and a few other elements. The traditional terracotta is stable when fired at 960 to 1 040°C, but has a high porosity and can only be used for fermentation and short-term storage. The inside can be lined with beeswax to limit the permeability, but this can weaken over time. MODERN AMPHORAE In 2010 a so-called “modern terracotta” was developed in Italy. It consists of clay, which can be fired at a higher temperature of between 1 200 to 1 260°C. This higher temperature causes smaller pores, resulting in amphorae with an OTR similar to oak barrels. Through further product evolvement, the OTR of amphorae can be adjusted to meet the requirement of cellars. ALTERNATIVE VESSELS Alternative vessels can also be made from mixes of concrete and ceramic. Although concrete is porous, it is not so permeable and favours the adherence of tartrate layers. This will block the pores of the vessel and consequently change its OTR. Stoneware alternative vessels are made from quartz/silica, feldspar, and white clay. When fired, it has an OTR lower than wood barrels, but this can be increased by adding terracotta and other material to the mix. Different parameters like the composition, firing temperatures, and duration of the firing of various non-wood vessels will determine its OTR or micro-oxygenation compared with wood barrels.

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WINETECH TECHNICAL YEARBOOK 2022