A New Breed of Wine Amphoras – Measured Porosity, Oxygen Transfer Rates and New Innovations

by Deborah Passin, VinEthos

Amphoras have been used to ferment and age wine for thousands of years. And for thousands of years they served the wine community well. But as winemaking techniques and wine quality have evolved since, say, 6000 BC or so, the technology that goes into making amphoras has failed to keep up.

Until now. Thanks to innovative amphora producers who have dedicated the last several years to research and development, there’s a new breed of amphoras: those that promise measurable and certified quality, utility and reliable efficacy. They can even be customized according to the needs of each winemaker.

Wineries can finally experience the true benefits of amphoras – slow and steady micro-oxygenation under a naturally controlled temperature and a pure expression of fruit and vineyard without any distractions.

Only one thing holds winemakers back from these much-improved amphoras: information. Many don’t know about this new generation and the latest innovations because the amphoras are new to markets outside of Europe. They’re big in Europe though, and for good reason. Walk with me…

Amphoras defined

It’s important to define what we mean by “amphora” before making any comparisons. Amphora-like vessels have many names – amphorae, jars/jarres, jugs, qvevri (Georgia) and tinajas (Spain). Traditionally, amphoras are oval-shaped and taper toward the base. Today we have a great variety of shapes and sizes to accommodate different winemaking needs.

Modern amphoras usually stand upright, but some are made to lay horizontal. The most commonly used material for wine amphoras is clay, including terracotta. Other materials used are sandstone (grès) and concrete, but those are not usually referred to as amphoras. 

Comparison to barrels – micro-oxygenation

An amphora can supply a similar level of micro-oxygenation as a new oak barrel. However, with a barrel, the micro-oxygenation process is not linear. Fifty percent of the annual oxygen transfer is released in the first 2-4 months and then slows down.

With a high-quality clay amphora, micro-oxygenation is more linear and stable year-round. When well maintained, an amphora will provide a similar level of micro-oxygenation year after year for its entire lifetime (that can be forever, by the way), which means there is more consistency.

This is possible because of high-temperature firing (a new method), which limits porosity and, therefore, prevents molecular changes to the vessel due to contact with wine. Wood absorbs more liquid, making it more variable, in addition to increasing wine loss and being harder to clean.

New Innovations

Working with innovative amphora producers is key to making high-quality amphora-aged wines. Common complaints about traditionally-made amphoras are: too much oxygen, flavors imparted from the amphora, cracks and leaks, and difficulty of sanitizing.

There are significant new innovations, though, that have changed what’s possible with amphoras. We’re going to get a little technical here, but bear with me. It’s some important stuff:

1. Precise porosity. Manufacturers can measure porosity levels as defined by the radius of pores in units of microns, also known as micrometers (µm). Here are the measurements from two producers of clay amphoras available in the U.S.

Montecchio (Impruneta, Italy)
Porosity is between 0.4 to 1.1 µm

TAVA (Trento, Italy)
Porosity is 0.05 +/- μm

As a comparison of materials, Vin et Terre jarres made from grès have an average 0.004 µm. Drunk Turtle from Tuscany makes its vessels from Cocciopesto (blend of stone, sand, marl and terracotta) or concrete. If lined with epoxy or tartaric acid, the porosity starts at zero then increases over time, introducing variability. Yet porosity stays lower than the Montecchio amphoras (above).

To make amphoras with more precise porosity (smaller pores), it’s necessary to fire them at very high temperatures (above 1900 degrees F). That’s previously been impossible with clay as the vessels can crack at those temperatures. TAVA, though, has developed and patented a new 100% natural clay mixture that’s more durable at these higher temperatures, which allows for smaller pores and better precision.

Traditionally-made amphoras: 960 °C (1760 °F) to 1040 °C (1904 °F)

TAVA: 1200 °C (2192 °F) to 1260 °C (2300 °F)

2. Applications of porosity to Oxygen Transfer Rates (OTR).

With barrels, we talk about OTR rather than porosity, but most manufacturers don’t quantify OTR with amphoras, with the exception of TAVA.

For comparison, the latest research on oak barrel OTRs are as follows:

American oak:  11.3 mg/L per year (.94/mg/L/month)
French oak: 8.18 mg/L per year (.68/mg/L/month)

TAVA’s most popular amphora has an average OTR of 1.5 mg/L/month (porosity 0.05 μm). But, if required by customers, the amphoras can be customized with levels as low as .4 mg/L/month and as high as 10 mg/L/month.

Another producer, Novum Ceramics in Oregon, doesn’t measure porosity or pinpoint micro-oxygenation levels for its amphoras but has seen dissolved oxygen content in wines approximately 5% above a new barrel.

It’s important to note that there is currently no single protocol for measuring micro-oxygenation in wine vessels. Methods and standards vary, making comparison difficult. TAVA is working with the Research Institute Edmond Mach (one of the most prestigious in Europe) to define, track and certify the level of micro-oxygenation over long periods of time, thus offering even greater reliability to winemakers.

3. Reduced migration of materials.

The testing of elements released by amphoras can be key in preventing undesired surprises in a wine (tartaric precipitation, changes in pH, etc.). TAVA has been working with two independent laboratories in Italy to develop new testing that could facilitate stricter regulations and standardize measurements for the amphora industry as a whole.

TAVA’s testing has revealed that amphoras fired at higher temperatures have less, or no, migration of elements and fewer chemical changes to the wine. For example, wine aged in amphoras fired at lower temperatures (conventionally-made) had much higher levels of calcium. In addition, the acid levels of these wines were lower – presumably there’s a correlation.

Calcium Levels (red wine stored in 30L amphoras for 1-2 months)

TAVA = 3.48 mg/L
Conventionally-made Amphora A = 189.18 mg/L
Conventionally-made Amphora B = 241.01 mg/L

Amphoras fired at higher temperatures could more effectively preserve the natural chemistry of a wine – a positive step forward.

4. Ceramic lids. Most modern amphoras use a stainless-steel lid to form a hermetic seal. The downside is that the steel acts as a thermal bridge, making wine temperature less stable. Clay is a thermal regulator, and some innovative producers offer new hermetically-sealing ceramic lids that minimize temperature fluctuation.

5. Durability. One of the reasons clay amphoras need to be fired at lower temperatures is that they’ll either break during high temperature firing or they’ll be more prone to cracks and leaks. But as clay mixtures have advanced, amphoras can handle higher temperatures and are less prone to cracks and leaks.

6. Easier to clean/more sanitary. Like barrels, amphoras that have high porosity (larger pores) let the wine penetrate deeper, making cleaning and sanitizing more difficult. In modern amphoras with smaller pores (fired with higher heat), the wine only penetrates 1-2mm.

7. Accessories for convenience.  Add-ons such as doors, drain holes, valves and sample taps ensures that fermenting, aging and cleaning amphoras are no more difficult than barrels or tanks. An amphora tipper can be handy to make the removal of skins a breeze. Suppliers also offer heating or cooling systems for the larger sized amphoras (available with both Montecchio and TAVA).

8. Larger sized clay amphoras. Only the most modern production techniques allow for making larger-sized amphoras while maintaining original reliability performance. So far, the two largest clay amphoras are made by TAVA and Montecchio – each are 1600L. There are larger sizes available, but they’re made from sandstone or concrete. The shapes of these two vessels are very different.

There are so many great benefits to using clay amphoras in winemaking: natural micro-oxygenation without added flavors/aromas, temperature regulation, preservation of wine freshness, cleanliness, and bonus, they last forever when well maintained.

Thanks to the latest innovations, amphoras are more useful and effective for winemakers today and can reveal unique characteristics in a wine that might have previously gone undetected. There’s an opportunity to craft even greater wines in a way that was never possible before.

References:

del Alamo-Sanza, M., and Nevares, I. (2014). Recent advances in the evaluation of the oxygen transfer rate in oak barrels. J. Agric. Food Chem. 62:8892–8899.

TAVA 

Bouchard Cooperages 

Novum Ceramics