Category: Wine Science

Serving temperature can have a profound impact on both the taste and mouthfeel of wine, so part of my getting ready to taste wines with customers is to figure out what temperature I want to serve them at. A consideration of the grape varieties and the wine style usually provides a good starting point, but there can be surprises.

Sometimes many surprises.

Recently, I received several proprietary blends to evaluate from a new producer than I am working with. Because I didn’t know exactly what was in each wine I had to make some guesses about serving temperature and I, er, um, guessed wrong. Multiple times. As I was tasting through the sample bottles, I really started to feel a bit like Goldilocks… “This wine is too warm! This wine is too cold!”

There are many ways that temperature affects how we perceive wine. A cooler wine gives off less aroma than a warmer one. Because smell is a big part of taste, this changes both what goes on in your nose and what happens in your mouth. Make a wine too cold, below 40°F or so, and it won’t have much of any flavor at all (which, it should be noted, can sometimes be an advantage with less delicious wines). At the other extreme, as wine gets too warm (above 70° to 75°F), the alcohol starts to take over, masking the taste and giving an unpleasant burning sensation.

A lower serving temperature can give a wine more body and, on warm days, make a wine more refreshing. It also reduces the tongue’s perception of sweetness, which is why ice cream tastes great when cold but overly sweet when melted. On the other hand, acidity, bitterness, and astringency (tannin) are all more noticeable in cool wine than warm.

Commonly given advice is to “serve white wines chilled and red wines at room temperature.” This leads people wrong in a number of ways. All too often “chilled” becomes “straight from the refrigerator”, a temperature that is almost always too cold. Similarly, “room temperature”, especially on a summer day or when the room is the kitchen, is likely to be too warm. Even when it isn’t, many red wines will benefit from being chilled slightly below what most of us would consider a comfortable room.

As with many other things about wine, the right serving temperature depends on which bottle you have in front of you. The chart below gives approximate temperature ranges for serving red, white, and rosé wines. Richer, fuller wines will typically be best in the warmer part of the range. Lighter or sweeter wines towards the cooler part (with the combination of light and sweet served coldest). Sparkling wines also are served at lower temperatures as cold helps keep the carbon dioxide in solution, preserving the bubbles and keeping the wines from becoming too frothy.

When chilling wine, allow about 30 minutes of time in the refrigerator for every five degrees cooler you want to make it. If you’re in a hurry, use an ice bath– then you only need to allow about 2 minutes per five degrees. Wine warms up quickly in the glass, and it is usually a good idea to have the bottle just a little cooler than “perfect” to allow for this. If you need to warm up an entire bottle, plan for about 15 minutes per five degrees in a 70 degree room. (In a warmer room it will take less time.)

Returning to our narrative, the fairy tale solution of opening new bottles until finding one that was just right was unavailable to me, so I was just going to have to work with what I already had. The wines that seemed too thin or sweet I chilled a bit more. The ones that seemed odorless or flavorless I let warm up a bit. And when I went back to re-taste them all, things were much better.

The moral of the story is listen to your taste buds. (Well, that and… the bears should be truly thankful Goldilocks didn’t find the key to the wine cellar!) By taking advantage of the ways the temperature affects the perception of wine you can make it more enjoyable. Besides, your taste buds work differently than everyone else’s– maybe a little experimentation will help you discover why your friends are raving about a wine you think is only so-so. After all, the three bears prove that even in a fairy tale not everyone likes things the same way.

As fabulous as wooden barrels are for aging wines, they have one tremendous drawback: expense. They are costly to buy and difficult to clean. The wood will contribute aromas and flavors to wine for only one or two aging cycles, necessitating frequent replacement for many styles of wine. Taken altogether, the expenses of using wood barrels can add dollars per bottle to the cost of producing wine.

There is a barrel material that has none of these problems– stainless steel. Stainless steel containers are cheaper to produce than wood, easier to clean, require far less maintenance, and last virtually forever. They are also completely non-reactive and non-porous, adding nothing to the flavor or mouthfeel of a wine. For all these reasons and more, stainless steel is widely used for fermentation, even for wines that will be aged in wood barrels. The problem comes after that….

Left to their own devices, wines matures in stainless steel tend to have bright fruit flavors and a crisp mouthfeel. This is a style that some prefer, especially for lighter wines, but it also lacks the depth and complexity that wine lovers have come to expect for so many kinds of wine.¹ To be able to take advantage of the cost savings offered by aging in stainless steel, winemakers have had to find ways to reproduce the sensory characteristics derived from wood barrels in their production processes.

One of these techniques, called micro-oxygenation, is the controlled release of small amounts of oxygen into wine through a ceramic disk placed at the bottom of the barrel or tank. The ceramic breaks up the oxygen into microscopic bubbles that are quickly absorbed by the wine.

Originally developed in southwestern France during the early 1990s to speed the maturation of wines based on the highly tannic Tannat grape, micro-oxygenation has been adapted for a wide variety of vinifcation uses, including helping wines maturing in stainless steel to develop in a manner similar to wooden barrels. For this purpose, “small amounts” means somewhere around 1 milliliter of oxygen per liter of wine per month! A detailed discussion on micro-oxygenation can be found it Duane Alexander Blaauw’s dissertation Micro-Oxygenation in Contemporary Winemaking on the Cape Wine Academy website.

With micro-oxidation imitating the slow infusion of air through wood barrel walls, the other part of the equation is incorporating wood derived aromas, flavors, and mouthfeel enhancements into wine being aged in stainless steel. This is commonly done by putting pieces of toasted wood in with the wine.

There are several advantages to this approach. While the pieces of wood interact with the wine in much the same way as barrel staves, they are much cheaper to produce as they don’t require precise shaping or bending and don’t have to be watertight. Putting the wood into the wine means that both sides (as well as the edges) are in contact with the wine, so that 100% of the wood surface area is used (as opposed to about 40% in a barrel). Lastly, the problem of cleaning the wood is avoided because the inserts are discarded after use.

The method that most closely mimics barrel aging is mounting long planks of toasted wood inside the stainless steel container. Lower-cost options include the use of shorter boards, wood cubes or chips, wood shavings, and even wood powder or sawdust. Smaller pieces tend to contribute aromas and flavors faster than larger ones, a fact that winemakers can use to reduce the production time of wine, albeit at the expense of the advantages that come from longer aging.

When combined with micro-oxygenation, the results of the plank technique have generally been good and it is widely considered a viable alternative for producing high-quality mid-priced wines. Similarly, wood cubes and wood chips can work well in younger wines. A 2011 study² showed little difference in consumer preference for young wines aged for 6 months in oak barrels versus 6 months in stainless with oak chips added for the last month. (In fact, the oak chip wines scored higher than the barrel aged ones, though the difference was not statistically significant.) Wood shavings and wood powders are generally considered less effective than the larger pieces of wood but do impart some wood character at a low cost and with minimal contact time.

One final method for adding wood flavors and aromas to wine is the use of wood extract. Made by soaking oak chips in high-proof alcohol, extract tends to be harsh but can provide an instant infusion of wood-like character into a wine. (A common use for extract is to fine tune the flavor of inexpensive wines after dosing with wood powder and filtering.) It’s quick and cheap, and that’s probably all that can be said for it.

The general consensus in the industry is that when wood character is desired, the aging of wine in wooden barrels yields the best wines. However, most will also agree that when used to emulate (and perhaps gently accelerate) traditional methods, the techniques discussed above are capable of producing good wines at lower cost. However, as the focus shifts from emulation at a reduced cost to imitation at the lowest possible cost, the results are predictably of lower quality.

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¹ For those who have been following this series, it should come as no surprise that this difference in flavors has resulted in yet another style of wine. After aging part of the wine with wood and part in stainless steel, the two are blended back together. The resulting wine can have a mixture of the bright fruit flavors coming from the stainless portion and the rich mellow notes from the wood.

² Pérez-Magariño, S., Ortega-Heras, M., and González-Sanjosé, M.L. 2011. Wine consumption habits and consumer preferences between wines aged in barrels or with chips. Journal of the Science of Food and Agriculture 91: 943-949.

Wood barrel aging has been called the winemakers spice rack. In the same ways that herbs and spices make foods more delicious, the aromas and flavors derived from wood can enhance wine. An earlier post discussed the effects of the different types of wood used in wine barrels, but that’s just the beginning. There are many other factors that affect the final result. For example, toast.

Toasting is something that occurs as part of the barrel-making process. When it is time to bend the barrel staves into their final shape, they are heated. In addition to making the wood more pliable, this also causes their inner side to brown, or toast. As the heat penetrates the staves, it triggers chemical changes that mellow the wood, reducing harsh tannins, diminishing woody flavors, and promoting the development of pleasing sensory characteristics.

By controlling the amount of heat and the duration of warming, barrel makers adjust the style and level of toast, achieving a wide variety of aromas and flavors including butterscotch, vanilla, caramel, chocolate, roasted coffee, and smoke. Toast is one of the specifications included when ordering a barrel, and it is an important part of shaping the future wine. (For more information on barrel toast, I recommend a visit to the website of the Seguin Moreau Napa Cooperage, where there is a detailed discussion of the topic.)

Having selected the flavors available through wood type and the toast level, the next decision is how much spice to add. To minimize the effect of the wood, very large neutral barrels (ones that have been used many times for aging similar wines) are best._* When large flavor contributions are desired, newly constructed barrels in small sizes are the way to go. A balance between these two extremes is obtained by employing a mixture of new, used, and neutral barrels. The actual mix selected by the winemaker is often disclosed on wine labels or data sheets with phrases like “100% oak aged, 30% in new barrels”.

Winemakers can also control the effects of aging through the length of time the wine spends in the barrel. This is an especially useful approach, as the progress of the wine can be monitored via barrel samples and changes applied as necessary. For example, if the wine has enough wood influence but would still benefit from more interaction with air, it can be racked (transferred) to neutral barrels. When sampling indicates that enough time has been spent in barrels, then it will be bottled.

One of the interesting things about barrel aging is that the oxidation and evaporation effects resulting from the porosity of the barrel walls accumulate at a fairly constant rate, but what the wine draws from the wood itself decreases over time. This means that more aromas and flavors are extracted from the wood in the first few months of aging than in any similar period thereafter. To increase the effect of the wood on the wine, winemakers can use two, or even three, sequential agings in new wood barrels, a process described as 200%, or 300%, new barrel aging.

(Another technique for increasing wood influence, especially tannin extraction, is fermentation in barrels. Most winemakers believe that it is only suitable for use with new oak barrels and more powerful grapes like California Cabernet Sauvignon. Barrel fermentation is a labor intensive process that is only used in small batch wines.)

Finally, the influence of different types of wood can be incorporated into a wine by using a mixture of barrels. For example, to get the flavors of American oak with the mouthfeel of French oak, the winemaker can age part of the wine in each type of wood. This is another choice frequently disclosed on labels or data sheets with phrases such as, “100% oak aged, 80% in French oak, 20% in American oak.” Even when it is not disclosed, clues will be present. For example, the combination mentioned above would likely yield moderate vanilla, coconut, or cream flavors with a lush satiny mouthfeel.

A variation on this approach is to use barrels made of one type of wood or toast level with barrel heads of another. The heads of the barrel are the flat ends and they represent about 30% of the interior surface area, enough to add distinct flavor and texture notes to a wine. One example of this is called “toasted heads”, where the heads have a higher level of toast than the barrel itself, allowing the winemaker to incorporate both structural tannins and toasty flavors. Another example is the use of acacia wood heads with oak barrels, a combination that tends to tone down oak derived flavors while preserving the structural tannins and gradual oxidation effects of barrel aging.

The artistry of the winemaker is choosing among all these techniques to highlight the best features of the wine without trampling its character. As spices can transform plain food into an exquisite meal, wood barrel aging can create wines of amazing depth and complexity from simple fermented grape juice. And it’s all because barrels were better for moving wine than amphorae.

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^*In recent decades, barrels made of stainless steel have also been used to mature wine without adding flavors, though the result is not identical. Wines aged in stainless tend to be brighter and more fruit forward than those matured in large neutral wood barrels. They are also less likely to age well, and in most cases should be consumed while young.  There are, of course, techniques for influencing how wines develop in stainless steel and new stylistic options for winemakers resulting from its use. These (spoiler alert) are a topic for part 4 of this series.

The woods that the Gauls used for making barrels were oak and fir. When these were adopted by the Romans, oak proved to be more suitable for wine, and its use continues to this day. However, people being what they are, we can be pretty sure that just about every other kind of wood has been tried at least once for making barrels and probably for storing and aging wine. A handful have been up to the job.

Oak

Oak’s preeminence comes from the almost perfect combination of tantalizing aromas, enriching flavors, structuring tannins, and elegant mouthfeel that it can bring to wine. While the whole package can be overwhelming for delicate wines and is not suitable for use with all grapes, when employed judiciously, wines of incredible flavor, depth, and complexity can result.

As is true for the grapes that go into wine, the type of oak and where it comes from have an effect on the final result. The two extremes are American oak and French oak with the other European oaks generally viewed as being somewhere in between. American oak, a different species of oak than the others^*, is known for providing more flavor and less structure while French oak is biased the other way.

For me, the first indicator of which oak has been used in aging a wine is mouthfeel. American oak imparts a distinctly creamy sensation, one that wraps around your tongue, while French and European oaks have a more satiny or silky mouth feel that caresses your tongue. If that doesn’t make sense to you now, try a few and you’ll get it.

American oak generally contributes the fewest tannins and French oak the most. Eastern European (Hungarian, Russian, and Slavonian) oaks are described as providing less structure and sweeter aromas than French oak with moderate tannin impact. Caucasian oak is considered by some (but not all) to be the most restrained of the oaks and well suited to lighter wines, including whites.

In the flavor spectrum, if you get a predominance of sweet vanilla, coconut, or cream soda, you are probably tasting the influence of American oak. French oak is known for mild vanilla aromas with flavors that run to cinnamon, allspice, custard, and crème brûlée. Hungarian oak often comes across with a fuller mid-palate than French oak and a pleasant spiciness that has nutmeg, clove, and sweet oriental notes.

The choice of which kind of oak to use in aging wines is (naturally) up to the winemaker, but there are some general tendencies. French oak, the leading choice in wood aging for most French wines, is selected by winemakers around the world for its tannins, structure, and subtle flavor components. Eastern European oak fills much of the same role outside of France (and, at one time, was even preferred by many French winemakers). American oak is used with bigger, fuller wines, primarily in Spain, North America, South America, and Australia. Slavonian oak is widely employed in Italy because of its ready availability.

Chestnut

Flavors of caramel, toast, and honey are what Chestnut can contribute to wine. The wood also contains a lot of tannins, and wine aged in new chestnut can be so tannic as to be undrinkable. This effect is tempered by using older barrels, and fans of chestnut aging value the complex flavors, light tannins, and good fruit preservation that result.

Due to the more porous nature of the wood, barrels made of chestnut have much higher evaporation and oxidation rates than those built from oak. Because of this, chestnut barrels are generally viewed as being suitable only for short aging periods. One exception is Vin Santo which, aged for several years without topping up, embraces the effects of both evaporation and oxidation as part of the wine’s style. Some winemakers utilize chestnut for long term storage by coating the inside with wax (or, more recently, silicone). Chestnut barrels are used in Beaujolais, parts of Italy, and Portugal.

Cherry

Barrels made from cherry wood are traditionally employed in the production of Ripasso and Vin Santo style wines in Italy. Winemakers that use it prize the wood for its gentle contribution of light cherry and red fruit flavors that complement their wines. The wood is also known for significantly influencing wine color, making it redder and deeper.

Like oak, cherry wood contributes tannins to wine as it ages. Wines aged in cherry oxidize faster than they would in oak. This can shorten the aging process or become an integral part of the aging process for oxidized wines like Vin Santo.

Acacia

Of all the woods commonly used in winemaking, acacia is the most gentle. Winemakers that work with acacia note its ability to provide structure and oak-like mouthfeel while preserving the aromatic and fruit characteristics of the wine. Less toasty and woody than oak, it is well suited to white wines, delivering delicate citrus and floral notes with a possible touch of sweetness that would never be noticed in more powerful wines. Some winemakers describe acacia as tannin-free, while others feel that it adds small amounts of soft tannin to the wine.

Acacia is more porous than oak, resulting in higher wine loss and more frequent topping up. It is typically used when the winemaker wants a short (3 or 4 month) period of conditioning before bottling.

Acacia barrels are common in Austria. They are used in Bordeaux, Sauternes, Loire Valley, and Gailac, commonly with sweet white varieties such as petit manseng, muscadelle, and mauzac. Acacia enjoys a broader range of use with Bordeaux, Burgundy, and Rhone white varietals. In the U.S., acacia is employed for aging sauvignon blanc, pinot blanc, viognier, chardonnay, and pinot gris.

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^*American oak is a species named Quercus alba, while two species of oak are used for barrels in Europe, Quercus robur and Quercus petraea. The two European oak species are often considered the same for wine making purposes (and are typically intermixed in barrel construction) though some sources express a preference for one over the other.