The Diurnal Difference

diurnal 3Simply put, an area’s diurnal temperature variation is the difference between the high temperature and the low temperature of a single day.  That’s easy enough to understand…but as a perpetual wine student, I hear (and use) this term all the time – and wanted to know a bit more about this “diurnal swing” and the factors behind it. Thus began another wild internet search for information!

Here are some of the more interesting things I discovered:

1: Diurnal temperature variation throughout the world varies from a low of approximately 7°F/4°C (experienced in Hong Kong in July) to 100°F/56 °C (the Guinness World Record, set in Browning, Montana in January of 1916). On average, most locations experience a diurnal temperature swing of 20-30°F/12-17°C.

2: To understand the diurnal temperature variation, we need to understand how the portion of the earth that we inhabit warms up and cools down. Basically, there are two sources of heat: the sun (solar radiation) and the ground, which slowly absorbs the sun’s heat over the course of the day. After the sun sets, the ground begins to radiate its stored heat back out, heating the air until it is depleted, which on a hot, humid day usually occurs right around dawn.

3: Diurnal swing generally decreases with proximity to the sea and other large bodies of water, and increases with the impact and amount of solar radiation. Other factors include elevation, humidity, day length, and clouds; as described below.

  • diurnal 4Elevation: High-elevation vineyard regions brag about their large diurnal swings for good reason: as mountain areas are located further from the large expanse of sun-heated ground surface, they receive less heat-radiation energy as the ground cools at night – meaning they cool off faster than do the surrounding valleys.
  • Humidity: Water vapor in the air very efficiently absorbs radiation – both solar radiation and radiation that is released from the ground.  This reduces the amount of heat reaching the ground, keeping daytime temperatures low (although we humans may not always appreciate this), and also reduces the amount of heat released from the ground – keeping the ground warm and nighttime temperatures high. The lack of humidity is one of the main factors that desert areas are known for large diurnal temperature swings.
  • Day length: Longer days understandably make for more heating, which can equate to larger diurnal variations. Day length in terms of daylight hours is determined by season as well as geographic location – high-latitude areas closest to the poles have longer days in summer, and shorter days in winter than those closest to the equator. In locations close to – or on – the equator, day length may vary by a mere 7 minutes over the course of a year!
  • Clouds: The presence of clouds decreases the diurnal swing. During the day, clouds absorb and release sunlight, reflecting heat radiation back out into space – making for less heat overall. On cloudy nights, heat is trapped near the ground, making for warmer nights – and less day-to-night variation.
  • Wind: Winds can cause the warm air radiating off the ground to mix with the cooler air a few feet above; thus mixing the warmer and cooler air and resulting in a decrease in diurnal swing.

We all know that diurnal temperature swings can be conducive to viticulture, by allowing the grapes to develop their sugary ripeness during the warm days, while still allowing the grapes to hold onto high levels of acidity when photosynthesis shuts down at night. Hopefully now – we also know why and how these fluctuations can occur!


Five Fast Facts about Fritz

Zerigelt 1Fritz Zweigelt, that is – and the grape he created.

#1 – Zweigelt is the leading red grape of Austria. It is also planted in small amounts in Canada, in both Ontario and British Columbia. Zweigelt is the third most-planted grape of the Czech Republic, where is goes by the name Zweigeltrebe. A few wineries – including Wilridge Winery and Perennial Vintners – have some small plantings (a few acres or so) in Washington State.

#2 – Zweigelt is a cross of St. Laurent and Blaufränkisch/Lemberger created by Fritz Zweigelt in 1922. Fritz was working the Federal Institute for Viticulture and Pomology at Klosterneuburg, Austria at the time, which makes the Zweigelt grape a true native Austrian. It was made with the purpose of creating a red grape unique to Austria that could thrive in the cool climate, be disease-resistant, and create a red wine of medium to full body and flavor.

#3 – Dr. Zweigelt did a good job – the grape that bears his name is indeed cold-hardy, drought-resistant, and thrives in a variety of soils. It is fairly disease-resistant, but is susceptible to powdery mildew (that’s Oidium to you CSW students) and berry shrivel/grape wilt.

Zweigelt 2#4 – The name of the grape is pronounced “TSVYE-gelt” – and if you think that’s difficult to say, consider yourself lucky. The original name of the grape was Rotburger (the name of a town close to where the grape was created) but was later changed to honor its creator.  Zweigelt also goes by the name Blauer Zweigelt. By the way, don’t confuse the original name of Zweigelt – Rotburger – with the grape that goes by the name of Rotberger (who would – ha!). For the record – Rotberger (“berger with an e!”) is a white grape cross of Riesling X Trollinger.

5 – As with all wines, the characteristics of a good Zweigelt vary according to vineyard conditions and wine-making techniques. Cool-climate, unoaked versions from Austria’s northern reaches are typically violet-red in color, medium-bodied, and moderate in tannins with fruit-forward flavors favoring red and black cherry. As such, it is the most widely consumed red wine in the pubs, bars, and casual restaurants in and around Vienna. The warmer growing regions in the areas of Lower Austria (Niederösterreich) – particularly  Neusiedlersee – produce full-bodied, richer wines with firm tannins. Such wines are often oak-aged, resulting in flavors of red cherry, red plum, cinnamon, and black pepper.


Five Fascinating Facets of Flor

Bodegas Hidalgo La Gitana (producers of La Gitana Manzanilla) in Sanlúcar de Barrameda – photo by Caleteron via Wikimedia Commons

Bodegas Hidalgo La Gitana (producers of La Gitana Manzanilla) in Sanlúcar de Barrameda – photo by Caleteron via Wikimedia Commons

Ok, I apologize for the gratuitous alliteration, but you have to admit…flor – the indigenous yeast cells that form a “veil” on the surface of certain types of Sherry as it ages – is fascinating. Flor (meaning “flower” in Spanish) is a subject that just seems to get more interesting the closer you look. As a matter of fact, I had a hard time limiting the information I found to just five facets!

#1: Flor is what separates the Finos from the Olorosos. Flor is a film-forming yeast (actually, several related strains of yeast) that is indigenous to the region around the Jerez-Xérès-Sherry DO. Flor is the main factor that causes the myriad types and styles of Sherry to divide roughly into three camps – Fino, Hybrid, and Oloroso – based on the extent of flor influence. Fino Sherries (such as those labeled as Fino or Manzanilla) are aged under the somewhat constant influence of flor. Oloroso Sherries (labeled as Oloroso or sometimes as Cream Sherry) are aged entirely without flor; while hybrids (such as Amontillado and Palo Cortado) are aged partially with flor and partially without.

#2: Flor is that “something in the air” in Jerez. Flor imparts its magic by finding its way from the air to the young base wines being prepared each year. The flor starts to develop in the base wines, and, after the wine is fortified – as long as the maximum level of alcohol remains around 15% by volume or less – and placed in a barrel, the yeast will reproduce and start to form a veil (velo in Spanish) that covers the surface of the wine in the barrel like a blanket.  The veil has been described as a waxy foam, about two centimeters thick; or as a light “cottony” film. The “blanket” formed by flor is sturdiest and palest in spring and autumn and turns rather thin and grey in summer and winter. Talia Baiocchi, in her new book “Sherry: The Wine Industry’s Best-Kept Secret” describes a thick film of flor as resembling a “1970s popcorn ceiling.”

Sherry barrel with transparent front to demonstrate the natural development of flor - Photo by El Pantera via Wikimedia Commons

Sherry barrel with transparent front to demonstrate the natural development of flor – Photo by El Pantera via Wikimedia Commons

#3: Flor protects the wine from oxidation in a variety of ways. The veil that is created via the action of flor protects the wine resting beneath it in a myriad of ways. For one, it simply forms a protective barrier between the wine in the barrel and the oxygen above it. In addition, the flor actually consumes some of the oxygen around it, as well as some of the alcohol, glycerol, and (if present) sugar. Thus, Fino Sherries tend to be pale in color, light in body, and bone-dry.

#4 – The collective effects of flor – referred to as “biological aging” – are amazing. The main benchmark for biological aging is considered to be the wine’s aroma. Simply put, contact with flor (both while it is alive, and after it expires and sinks to the bottom of the barrel as lees) may create up to 1,000 milligrams per liter of acetaldehyde in the wine. That is, according to Ruben Luyten of the blog Sherry Notes, more than twenty times the amount of acetaldehyde found in most table wines.  Acetaldehyde’s aromas have been described, variously, as rancid apple, apple cider, almond, hazelnut, and even straw or hay. The presence of flor will also lead to an increase of in other highly aromatic compounds, such as lactones and terpenes, which may add an array of aromas – from dried herbs to green walnuts, mushrooms, and baking spices – to the wine.

#5: Flor has some definitive preferences as to climate and conditions.  Flor can only survive in wine that has an alcohol level of somewhere below 15% abv – but that’s just the beginning of its ways. Flor also needs a good deal of humidity in the air, which explains why Fino Sherries thrive in certain areas, such as the cooler, coastal areas around Sanlúcar de Barrameda and El Puerto de Santa María, while Oloroso Sherries (which are aged without flor) thrive in the hotter, drier, more inland areas around Jerez. It is well-known that solera systems (and the buildings that surround them) are often at ground level (as opposed to an underground cellar) and built with high ceilings or even left partially open to the elements, so as to encourage air flow. It’s also rumored that bungs are left gently in place in Fino Soleras to encourage the movement of the humid air inside the barrels.

Flight of Fino Sherries at London’s Bar Pepito – Photo by Ewan Munro via Wikimedia Commons

Flight of Fino Sherries at London’s Bar Pepito – Photo by Ewan Munro via Wikimedia Commons

While wines produced “under a veil” are somewhat uncommon around the world, there are a few shining examples besides Fino Sherries. These include the Vin Jaune of France’s Côtes du Jura AOC, certain types of Tokaji, a “Vin de Voile” produced by Domaine Plageoles in France’s Gaillac region, and the “Condado Pálido” produced in Spain’s Condado de Huelva DO, among others.  While these wines undergo a similar style of biological aging, it is not certain that they use the same strain(s) of yeast as are found in Jerez-Xérès-Sherry, and, of course, each of these wines is made in its own conditions of climate-atmosphere-terroir. Thus, we can safely say that there’s nothing in the world quite like the flor of Jerez, the protective foam-blanket it creates, and the resulting Fino Sherry.


Five Cognac Curiosities

Cognac CuriositiesAll good wine and spirits students know that Cognac is a high-quality French Brandy, made from grapes grown in the delineated Cognac region, located just north of Bordeaux. There are several grape varieties allowed, of which Ugni Blanc (aka Trebbiano) is the preferred; the ferment goes through a double distillation in an Alembic still, followed by a minimum of two years’ aging in oak. Good! We’ve covered the basics. But did you know…

#1 – The product of a third distillation is known as “Espirit de Cognac.” Espirit de Cognac was awarded an AOC in 1936, and is an unaged product that – after hours and hours of distillation – comes off the still at 80 – 85% abv. Brandy lovers of the world, don’t feel bad if you think you’ve never had Espirit de Cognac. In reality, you actually might have – as all of the production is destined to be used in the “liqueur d’expedition” for sparkling wines such as Champagne.

#2 – Don’t confuse the unaged, bound-for-bubbly “Espirit de Cognac AOC” with a product labeled as “L’Espirit de Cognac.” Many Cognac producers use the term “L’Espirit” to designate their top-tier bottles. For instance, “L’Espirit de Courvoisier” is an assemblage of old cognacs – the oldest is rumored to be from the 1802 vintage (“the few precious drops that escaped Napoleon’s lips”), and the youngest from 1930.  Bottled in a numbered, hand-crafted Lalique crystal decanter, L’Espirit de Courvoisier sells for upwards of $5,000 per bottle – if you can find one.

Cognac grapes#3 – Cognac is distilled from a white wine base, which, according to the AOC, must be a minimum of 90% Colombard/Folle Blanche/Montils/Sémillon and/or Ugni Blanc. (In practice, Ugni Blanc is by far the dominant grape, accounting for up to 90% of the total vineyards.) A Folle Blanche X Ugni Blanc cross named Folignan may be used up to a maximum of 10%. Upon being authorized for use in Cognac in 2005, Folignan became the first cross variety produced at the INRA (Institut National de la Recherche Agronomique) to be authorized for use in an AOC.

#4 – Three other grapes are currently allowed to be used in the base wine as well. These are Jurançon Blanc, Meslier-St-François, and Sélect. However – it gets a little tricky here – they are only permitted through the 2020 harvest, and only if they were planted prior to September 18, 2005. Most of these grapes fall into the “uninteresting” category; however Meslier-St-François is (according to Jancis Robinson, et al, in Wine Grapes) a historic French variety that once grew in Champagne, the Yonne department of Burgundy, and the Loire Valley. As a matter of fact, in 1990, Charles Jumert of Cave de la Berthelotière “saved” the last surviving Meslier-St-François grapes of the Loire Valley by taking cuttings off of a vineyard as it was bulldozed under. He planted the grapes in Villiers-sur-Loir (north of Tours) and has been making a varietal “Vin de France” from them since 2003.

Cognac curiosities 2#5 – 97% of all Cognac produced each year is exported. That’s right – only 3% of the Cognac produced, on average, is consumed at home. As a matter of fact, the French consume as much Scotch whisky as they do Cognac. This means that an average of 130 million bottles of Cognac are exported each year, which is enough to make grape brandy one of France’s most valuable exports. (As for France’s other valuable exports, #1 is airplanes (as in Airbus), #2 is medications, #6 is wine (as in yeah!), #9 is make and sun-tan preparations, and #13 is perfume (we knew those had to be in there somewhere). Number 18 is brandy, Cognac included – not bad. You can see the rest of the data on French exports here.

The Bubbly Professor is “Miss Jane” Nickles of Austin, Texas…

Creature Feature: The Glassy-winged Sharpshooter

This is NOT a picture of the glass winged sharpshooter. Glassy winged sharpshooters are NOT cute. There is a link to a picture of a real glassy winged sharpshooter at the end of this post.

This is NOT a picture of the glassy winged sharpshooter. Glassy winged sharpshooters are NOT cute. There is a link to a picture of a real glassy winged sharpshooter at the end of this post.

Every good wine student knows this: The glassy winged sharpshooter is a vector responsible for spreading Pierce’s Disease, and as such, is a known threat to commercial viticulture.

I’m right, aren’t I? You knew that? You have probably answered that question correctly on an exam, or even discussed the little guy fairly intelligently amongst your wine-loving friends.

But do you even understand what a vector is? (Hint: a vector is an insect that spreads disease.) And how well do you really know our friend with the glassy wings? Read on for a little insect insight!

The glassy winged sharpshooter is a common type of insect known as a leafhopper. There are over 20,000 different species of leafhopper, and they reach all over the world. Leafhoppers are closely related to, and share their insect family name – Cicadellidae – with cicadas and treehoppers, but are only distantly related to grasshoppers.

All members of the leafhopper family – who go by the nickname of “hoppers” – are plant feeders that feast on the sap of grass, shrubs, or trees. Their hind legs are built for jumping and they do just that – hopping from leaf to leaf, blade to blade, or tree to tree, inserting their needle-like mouths into the plants to lap up the juice. Hoppers are considered pests in many places as they can dehydrate the plants they feed on, causing havoc not just to grapes but to over 100 different plants all over the world, including oak trees, citrus trees, apple trees, and even coffee plants.

The name “sharpshooter” is used to refer to a group of large leafhoppers in the Proconiini branch of the family tree. In order to get enough nutrients, these insects filter a large volume of liquid sap through their digestive systems. Much of the excess water is then “squirted” forcibly away from the insect’s body in a fine stream – thus, the nickname “sharpshooter.” (I was hoping it was something a bit less gross, but there you have it.)

The glassy-winged sharpshooter is about ½ inch (12mm) long and has large, translucent (“glassy”) smoky-brown wings with red veins.  They are native to the South America, and migrated to California from the southeastern United States. They were not always considered a serious pest in the past; but once introduced to Southern California it became a serious threat to viticulture due to the ease and rapidity with which it can spread the bacteria that causes Pierce’s disease. Once the sharpshooter has acquired the bacteria, it will remain infectious for the rest of its life.

There are NO glassy winged sharpshooters in the pictures. These bugs are cute. Glassy winged sharpshooters are NOT.

There are NO glassy winged sharpshooters in this picture. These bugs are cute. Glassy winged sharpshooters are NOT CUTE.

The glassy winged sharpshooter remains a serious threat to viticulture in California and beyond. Due to its coloration, it is difficult to see in nature, despite its size. “Bug spotting” programs are underway in parts of California to help identify and prevent further infestations. Plant nurseries must confirm that their plants are “sharpshooter-free” and everyone is on the lookout. School children are taught to spot “sharpshooter rain” and many Californians are encouraged to have yellow sticky traps in their yards. Anyone who thinks they spot a sharpshooter is encouraged to call a hotline.

In the case of minor infestations, biological controls are used, including the introduction of various bugs – such as small wasps, spiders, and the praying mantis – that feed on the eggs. Chemicals (pesticides) are used in more extreme cases, but some of the more effective chemicals are also damaging to the wasps that help control the sharpshooters.

In other parts of the world, the glassy winged sharpshooter causes havoc by spreading phoney peach disease, oleander leaf scorch, and citrus X disease. The danged little glassy winged sharpshooter, it seems, remains a serious pest.

To learn more, and to see a picture of the glassy winged sharpshooter, visit the website of the Applied Biological Control Research Department at UC Riverside.

The Bubbly Professor is “Miss Jane” Nickles of Austin, Texas…

In Praise of the Juniper Berry

Fig 4-2 Juniper BerriesThe hero of gin lovers everywhere, the juniper berry is not really a berry at all but the seed cone of the juniper plant. Juniperus communis, the common juniper, is a shrub or small evergreen tree with needle-like leaves in whorls of three. Juniper often grows as a low-spreading shrub, but juniper trees can grow to over 32 feet (10m) tall. The juniper plant has over 50 species, and the largest range of any woody plant, thriving throughout the temperate zone of the Northern Hemisphere from North America to Europe and Asia.

Many cultures consider the leaves of the juniper to be a symbol of protection against disease and evil spirits. In Tuscany, a sprig of juniper is often placed in front of the door to offer protection to the house and its inhabitants. Juniper can also ward off snakes, at least according to the ancient Greek pharmacologist Pedanius Dioscorides, who claimed that the smoke from a fire of burning juniper could keep snakes away.

The “berries” of the juniper plant begin life a grey-green color, and ripen in 18 months to a deep purple-black hue with a blue waxy coating. Juniper berries are revered for their medicinal purposes, particularly as a diuretic and in regards to conditions of the kidney, bladder, and stomach.

Of course, to students of wine and spirits, the juniper berry is known primarily as the predominant flavoring in gin and other spirits such as Genever, Steinhäger, and Wacholder. The flavor profile of juniper berries is often described a pine-like, resin-like, intensely herbal and with bitter citrus notes. Noted author Harold McGee, in his book On Food and Cooking defines the flavor of juniper as “green-fresh.”

The Juniper Forest ("The Valley of Juniper) in Ziarat, Pakistan

The Juniper Forest (“The Valley of Juniper”) in Ziarat, Pakistan

Juniper berries are considered an important culinary herb, particularly throughout Scandinavia and Central Europe. Juniper is often used to impart a sharp, clean flavor to meat dishes – particularly game meats – as well as cabbage and sauerkraut dishes. Juniper has a natural affinity for pork and is found in many recipes for roast or braised pork. The recipe for Choucroute Garnie, a classic Alsatian dish of sauerkraut and meats, universally includes juniper berries.

One more thing: on Easter Monday, the young boys in Kashubia (Northern Poland) chase the girls in the town square, brushing (sometimes referred to as “gently whipping”) their legs with juniper sprigs. This is, according to tradition, to ensure good fortune in love to the “chased” young ladies. After watching this annual tradition unfold,  I am guessing, the parents would most likely appreciate a nice shot of gin.

The Bubbly Professor is “Miss Jane” Nickles of Austin, Texas:

Ten Tidbits on Tasmania

Tasmania VineyardTen Tidbits on Tasmania – Tasmanian Wine, that is!

#1 – The island of Tasmania is the southernmost state of Australia and lies about 150 miles south of the coast of Victoria, across the Bass Strait. Tasmania lies directly in the path of the fierce trade winds known as the “Roaring Forties” and as such, its west coast has a cold, wet climate.

#2 – Tasmania is Australia’s most mountainous state. The highest point is Mount Ossa in the northwest. Mount Ossa reaches peaks of 5,350 feet (1,620 meters) above sea level. The temperature climate necessary for viticulture in Tasmania is made possible by the multiple mountain ranges that criss-cross the center of the island. Most Tasmanian vineyards are located on lower slopes and valleys of these mountains, or in the rain shadow to the east.

#3 – As is to be expected considering its location, Tasmania has a maritime climate. Mild spring and summer temperatures, warm autumn days, and cool nights allow for the region’s grapes to enjoy a long, slow ripening with minimal loses of natural acidity.

#4 – Cool climate grapes dominate the viticultural landscape and include 44% Pinot Noir, 23% Chardonnay, 12% Sauvignon Blanc, 11% Pinot Gris and 5% Riesling. Other varieties include Cabernet Sauvignon, Merlot, and Gewürztraminer.  Tasmania’s cool climate makes it a natural for sparkling wines, and many of the sparkling wines produced in Australia are sourced with grapes grown in Tasmania.

Tasmania map#5 – Tasmania’s output is tiny. At last count, the state had just over 3,700 acres (1,500 hectares) of vineyards, and accounted for approximately 0.5% of Australia’s output. They even say that “more wine is spilled on the main land than is produced in Tasmania.” However – Tasmania’s wine production rose by more than 300% over the last decade, and quality is regarded as quite high.

#6 – According to, 100% of bottled Tasmanian wine retails for $15.00 or more – as compared to only 7% of Australian wines overall.

#7 – Tasmania’s first vineyard, planted in 1788, was a failure. The vines were planted by William Blight at Adventure Bay (on Bruny Island), but when he returned four years later they were gone. Vines were planted again in the early 1800s, and wine was made and sold commercially in Tasmania from 1800 through the 1860s. However, vine disease and the gold rush in Victoria (1851-1870) caused wine production in Tasmania to collapse by the 1870s.

#8 – In the 1830s, wines from Tasmania were brought to Victoria by William Henty. Henty sailed from Launceston in Tasmania to Portland in Victoria on the Schooner Thistle. Among his belongings were “one cask of grape cuttings and one box of plants.” These cuttings became the first vines planted in Victoria. At about the same time, vines from Tasmania were also among the first grapes planted in South Australia; John Hack (in 1837), and John Reynell (in 1837) both planted Tasmanian vines in South Australia.  Some say, based on these facts, that vines from Tasmania founded the wine industries of both Victoria and South Australia.

Map via

Map via

#9 – The beginnings of the modern era of Tasmanian wines can be traced back to the 1950s, when two Europeans, Jean Miguet and Claudio Alcorso arrived in Tasmania and, without knowing each other or what the other was doing, began planting vines and making wine.

#10 – While Tasmania does not have any officially designated wine regions or sub-regions within it, the following “unofficial” areas are generally used to describe those areas rich with vines:

  • In Northern Tasmania: The Northwest Coast, Tamar Valley, and Northeast/Pipers River
  • In Southern Tasmania: Coal River Valley, Derwent Valley, and Huon/Channel Valley
  • Straddling the Two: The East Coast

The Bubbly Professor is “Miss Jane” Nickles of Austin, Texas:


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