Ice Wine: A Special Gift of Nature Impacted by a Warming Globe

March 25, 2020, 5:24 PM EDT

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Above: Grapes waiting to be harvested under a specific set of weather conditions to produce ice wine, sometimes referred to as the true "nectar of the gods". (Iniskillin Winery)

This past winter season, Germany lost an entire harvest of a special type of wine referred to as ice wine. The culprit was a record warm winter for much of Europe, as a very mild weather pattern set up across the region for most of the winter. With global warming as a background modulator to wintertime temperatures, these types of “non-harvest” years for ice wine in Europe are becoming the norm rather than the exception. I thought it would be interesting to look at this unique wine, sometimes referred to as the true “nectar of the gods” for its delicately balanced sweetness, to learn more about its connection to weather and a changing climate.

I first learned of the term “ice wine” several years ago while visiting one of my favorite spots on Earth: Niagara-On-The-Lake in southern Ontario, Canada, just downstream from world-famous Niagara Falls. This amazing region is home to some of the best ice wines in the world as a result of its “terroir”, defined as how a particular region’s climate, soils and terrain affect the taste of wine.

As its name suggests, ice wine must have something to do with cold weather. In fact, it is a type of wine made from grapes that have frozen while still on the vine. In a perfectly choreographed dance of nature, the water in each grape freezes while sugars and other components are left outside the resulting ice. This results in a more concentrated grape juice. The “must”—the freshly crushed juice containing the skins, seeds, and stems of the fruit—is then pressed from the frozen grapes. The result is a smaller batch of more concentrated, very sweet wine. With ice wines, the freezing happens before fermentation, which is common to dessert wines. This gives ice wine its characteristic refreshing sweetness balanced by high acidity.

Natural ice wines require a hard freeze of 17–18°F or colder to occur sometime after the grapes are ripe. That means grapes may hang on the vine for several months following the normal harvest. But not just any freeze will do. If a freeze does not come quickly enough, the grapes may rot and the crop will be lost. If the freeze is too severe, no juice can be extracted. Wine makers not only monitor the local forecasts for the best conditions to harvest—their rows of grapes are interspersed with the highest-tech meteorological equipment, reporting temperature, humidity and other conditions at several heights throughout the fields.

The grapes also have to be protected by netting from animals, and birds in particular, who have been known to strip the vines clean in the late fall after all other grapes and berries are no longer around.

Finally, the grapes must be pressed while they are still frozen, which allows the ice crystals to penetrate the skin of the grapes, bringing out more flavor. However, that means pickers often will be working throughout the night for hours on end in the cold, while those who press the grapes have to work in an unheated space.

It doesn’t end there. The high sugar content of ice wine leads to a slower fermentation than other wines and may take many months to complete the process. Because of the lower yields resulting from by this process, and the additional challenges of the harvesting process, ice wines are significantly more expensive than table wines. But it’s obviously worth it. Even though there is a very high sugar content to the wine, it is very refreshing due to the balancing effect of higher acidity.

With such stringent climatological factors for ice-wine production, it is apparent that there are only going to be particular regions of the world where it can be made. In addition to a very select set of conditions regarding the terroir—including the make-up of the soil, the terrain, and even the aspect of the fields—you need temperatures to get warm enough to grow the grapes, then cold enough to harvest. In the Northern Hemisphere, this occurs across a specific latitude belt from Europe through parts of Asia and into North America.

Historically, the concept of an ice wine has been around for some time. In fact, there are mentions of a wine produced from frozen fruit all the way to Roman writings. In more modern times, ice wine production emerged across much of Central Europe, led by Germany, during the 19th century and continues through today. More recently, other parts of the world have discovered that they may also have the right stuff to produce ice wine, including parts of Japan, the United States, and Canada.

In fact, Canada is the world's largest producer of ice wines, producing a greater volume of ice wine than all other countries combined. The tiny wine-growing region of Canada’s Niagara Peninsula has emerged as a world leader in the production of ice wine. In the figures below, you will note that the Niagara Peninsula sits conveniently between two of the Great Lakes, Erie and Ontario. This affords the area a perfect microclimate throughout the year for the production of wine.

Why Europe’s ice wine harvest of 2019–20 failed

With such stringent limits on the weather conditions necessary for ice wine production, a changing climate and a warming globe can have serious negative impacts, especially to a wine-growing region that historically would experience temperatures cold enough for harvest only a few times each season, like Germany.

The winter of 2019–20 was the warmest on record for Europe. The European Union’s Copernicus Climate Change Service (C3S) estimated that temperatures across Europe were 2.5°C above the previous winter record (2015-16). The center’s data go back to 1979, but when comparing the data with other sources, C3S also said this was the warmest European winter going back to at least 1850. In Germany, it was the second warmest winter since records began in 1881, with only 2007 being warmer by 0.3°C.

As winemakers in Germany waited patiently for temperatures to drop to the magic range of 17–18°F, the overall mild weather pattern refused to budge. In fact, for much of the ice wine-making region, the temperature never made it down to the magic range at all.

Comparing this past winter’s daily minimum temperatures for the portion of Germany well known for ice wines vs. the Niagara Peninsula on the North American continent, the data reveals some interesting points. With the understanding that local topography can result in significant daily temperature differences, even on a scale from one location to an adjacent field, I used Stuttgart, Germany, as the proxy for the European ice wine location and Niagara Falls, New York, for the Niagara Peninsula. Below is a plot of the daily low temperature at each location and also the minimum temperature of 17°F required to harvest the grapes. As you can plainly see, Stuttgart had not one day in which the temperature dropped to the critical level this past winter.

Meanwhile, the Niagara Peninsula met the required temperature on no less than 25 days during the winter. A recent report noted that only one wine maker in all of Germany was able to harvest a tiny 100 liters of ice wine when the temperature briefly dropped in his fields for a few hours on one January night. The Niagara Peninsula, meanwhile, had another banner yield for ice wines. Despite the fact that the nearby Buffalo region had its ninth warmest winter in 147 years of recordkeeping, the peninsula still had enough cold nights in the “magic range” to produce a bountiful harvest.

What is to come with ice wine and the continued warming of the globe?

I look at Europe’s ice wine region versus North America in the same way I compare eastern versus western ski resorts in the United States. In the east, warming winter temperatures are placing the lower-elevation ski resorts in peril. They don’t have much breathing room when it comes to warmer winters. Even with the best snow-making equipment it may become too warm soon to sustain a healthy ski industry. Meanwhile, out west, ski resorts have a lot more breathing room when it comes to warming winter temperatures. They are at higher elevations, which means a colder climate that gives them a little better chance to survive even with rising temperatures.

When it comes to ice-wine making regions in Europe vs. parts of the U.S. and Canada in North America, Europe is like an Eastern ski resort. They are at a tipping point regarding winter temperatures. Yes, there will be winters in the future that get cold enough to produce an ice wine harvest, but they will likely be even more rare. In the Niagara Peninsula of Ontario, Canada they have breathing room. With winter airmass trajectories that often come from some of the coldest regions of North America, from the Canadian Plains to Quebec, they can almost always be assured of at least a few days where temperatures drop to those magic numbers for harvest.

As with many crops, a continuation of a warming planet will likely mean that winemakers will have to adapt. Different vintages will be planted, technologies will improve, and it’s not out of the question that wine regions themselves will be transplanted to areas that have a more favorable climate overall for the production of wine and ice wine in particular. I, for one, hope that ice wines stay around for a long time. If you get the chance, try some–you will never be closer to experiencing the exquisite taste of the sugar-infused grapes!

The views of the author are his/her own and do not necessarily represent the position of The Weather Company or its parent, IBM.

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Tom Niziol

Tom Niziol recently retired as winter weather expert for the Weather Channel after a 32-year career as a forecaster, science and operations officer, and meteorologist-in-charge at the National Weather Service office in Buffalo, NY. Tom has published several papers and taught forecasters around the world through the COMET Program. His keenest winter weather interest is lake-effect snow.

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