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Wine industry

Napa Valley winemakers using concrete eggs look for breathability, circulation in fermentation process

From the Napa Valley Wine Insider Digest: Sept. 4, 2021 series
  • Updated

What looks like the spawn of a post-apocalyptic creature or a mode of alien space travel, those giant concrete eggs you see around Napa Valley wineries are actually used for fermentation purposes.

A midway point between stainless steel neutral tanks and seasoned oak barrels, concrete eggs have been around for hundreds of years, though they are relatively new to Napa wineries. The vessels strive for neutrality in taste without sacrificing breathability and control over the product.

Cakebread Cellars and Cardinale Winery are two Napa Valley staples that use these cement eggs, with both entities accumulating their first a little over a decade ago. Both wineries note the circulatory benefits of having an egg-shaped tank, and over time, have learned how to manage the fermentation process to get an end product they are pleased with.

“At Cardinale, we use the eggs exclusively for our Intrada Napa Valley Sauvignon Blanc, [because] both the unique shape and the material of the eggs plays an important role by adding texture and mouthfeel to the wine,” said assistant winemaker Gianna Kelly. “Their unique shape allows the lees — all those solids that settle at the bottom of a fermentation vessel — to circulate and stay suspended in the wine longer.”

Kelly also says that the concrete’s porosity allows micro amounts of oxygen to enter the vessel — and thus the wine — which enables for chemical reactions sought after in a good bottle.

“Yeast love oxygen and happy yeast make for a happy winemaker,” she said.

Cardinale now has five concrete eggs being used for production, and Cakebread has risen to a room of 13. Aaron Fishleder, Cakebread’s Vice President of Operations, jokes that they now have their baker’s dozen, but it was a slow learning process to get to this point.

Instead of jumping in headfirst, both wineries started with one vessel before getting too far ahead of themselves, as there is definitely a learning curve when it comes to using a new wine tech. (Even if that tech has been around for hundreds of years.)

“It's a smaller fermentation vessel and what we like about it, because of the size and the mixing that occurs inside of the egg, is the mixing of the acids that we get out of those tanks,” said Fishleder. “We like the mineral flavors, which is probably related to the acids being lessened, that we taste as well.”

Both wineries also have temperature rods placed throughout the eggs so they can directly manipulate the temperature inside of the vessel, with an additional two kept in the Cardinale barrel cellar at about 50 degrees for their Sauvignon Blanc. This is important not only for the wine’s sake but also for the eggs’.

“The eggs do require a little extra care,” said Kelly. “For example, sudden temperature changes can crack the concrete, and given their weight we can’t move them around as easily as barrels or small stainless steel tanks.”

Since you can’t blast the tanks with hot water to sanitize them, each winery has a different system to clean the eggs after use. As a general rule, you also can’t mix red and whites between the barrels due to residual flavors.

“Instead, a gentle solution of water and baking soda helps remove the tartrates,” said Kelly of their 10-years-running, just-like-new vessels.

This is a bit more labor-consuming compared to sanitizing barrels or stainless steel tanks, so Kelly and Fishleder’s staff have to be particularly careful with the process.

“We don’t use any chemicals or anything abrasive so we aren’t scraping the inside of the tank, we are very gentle so we just use warm water and rinse it, so that takes some time,” said “It's the same amount of work as a big tank, just with a smaller vessel and less wine.”

“Less wine” still translates to nearly 500-gallon tanks, but relatively speaking, it is a commitment.

However, both Kelly and Fishleder encourage winemakers interested in the method to give it a go — preferably, one at first to learn the ropes — since they are so pleased with the product they have been creating with them.

“We really like what we are getting out of it,” said Fishleder. “We just finished our renovation in late 2019, so now we have a room full of eggs … We believe in this.”

Miguel Garcia shows how he uses technology to help sustainably manage the demonstration vineyard owned by the Napa County RCD.

You can reach Sam Jones at 707-256-2221 and

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Napa Valley wine industry reporter

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