Red wine production technology
Peter Bell

Parts two and three are devoted to a brief overview of the processes involved in red and white winemaking, and how they affect wine quality. The main intent is to make you aware of the myriad decisions facing the winemaker at every stage of wine production, and how a given decision at any time can have a dramatic effect, positive or negative, on wine quality.

The choice of grape variety (assuming that site selection is fixed) is the first occasion where style and quality are affected. It can be said with reasonable certainty that some grape varieties make better wine than others - for example, Cabernet vs. Concord ( I apologize to those of you who derive great pleasure from Manischevitz). It is less certain that, say, Chardonnay makes a better wine than Vignoles - that is entering the realm of subjectivity.

The main consideration should be the suitability of a grape variety to the climate. A Finger Lakes Zinfandel would clearly be a disaster, even though it is one of California's great grapes.

Grape varieties vary tremendously in their characteristics, most importantly color, flavor, and tannins. Compare Cabernet Sauvignon with Pinot Noir. The former makes a wine with an intense purple-red color, obvious astringency, and lots of flavor intensity. The latter makes a wine that could not be more different: it is usually mid-red or even pale red, the tannins are very supple, and the flavors are delicate rather than bold. These two grapes can never be made into the same style of wine.

The condition of the grapes at the time they are picked is absolutely crucial to wine quality. The potential of a crop of grapes for making the best possible wine can be utterly compromised by picking at the wrong time. The concept of Optimal Ripeness is a very important one. It can be seen as a time frame through which a crop of grapes passes, and it can last for as little as one or two days.

Grapes that are picked underripe tend to have sugar levels that are below those necessary for making wine in the normal alcohol range of 11-13%. Acid concentrations will generally be too high, affecting the taste of the wine. And given that 'correct' flavors usually only show up in grapes at close to full physiological ripeness, underripe grapes tend to make wines that taste 'green' and weedy.

In cool climates, nature often dictates when to pick the grapes. Disease pressure mounts as the season progresses, and it is frequently necessary to pick solely on that basis. Also, if a heavy, early frost is called for, winemakers often choose to bring in the grapes even though they haven't yet reached optimal maturity.

Grapes that are picked overripe can also make substandard wines. In warm areas such as most of California and Australia, growing conditions are such that if grapes are left on the vine, they will readily progress past optimal ripeness. Wines made from such grapes will have a dangerously high pH (Êunless corrections are made ), very low acid, too much sugar ( read:potential alcohol ), and very unattractive, stewed fruit or jammy flavors.

Some lucky winemakers work in conditions where they can actually take advantage of the ripening continuum to increase their blending options. In warm parts of Australia, for example, it was found that Cabernet Sauvignon harvested all at the same time tended to be a bit one-dimensional ( as well as making for a tank space crunch! ). Astute winemakers began harvesting over a range of ripeness levels, and in so doing were able to capture a much greater range of flavors. A typical blend might be:

Early Ripeness ( flavors of mint, herbs, green olive, stems; 'tight-grained' tannins ): 15%
Mid Ripeness ( flavors of berries; 'chewy' tannins ): 70%
Late Ripeness ( Port-like flavors; 'broad' tannins ): 10%
Very Late Ripeness ( Jammy flavors; 'chocolatey' and 'full-blown' tannins ): 5%

Harvesting

Grapes can be picked either by machine or by hand. (Experiments with having the picking done by deer, wild turkeys, sheep, birds and kangaroos have resulted in extremely low yields.) There are advantages and disadvantages to each. They can be summarized as follows:

Mechanical Harvesting:

-is fast: many tons can be brought in in a short time ( + )
-delivers only grapes, not stems ( usually +, unless winemaking protocol calls for stems )
-is often competitive in price ( + )
-can be hard on grape vines ( - )
-tends to include material other than grapes, such as insects, staples and birdnests ( - )
-does not allow selection of healthy grapes only or of botrytis-infected grapes only ( - )
-can be disastrous if the machinery breaks down ( - )

Hand Picking:

-does not significantly bruise the grapes ( + )
-allows for bunch selection ( + )
-makes for lots of good 'photo ops' for newsletter ( +++++ )
-rarely outpaces ability of winemaker to crush grapes ( + )

Another important option is the time of day that harvesting takes place. For obvious reasons, it is only practical to harvest at night if a mechanical harvester is used. Nighttime picking is often employed in warm winegrowing regions so that the grapes are cool when they come into the winery; this saves on energy and decreases the likelihood of juice oxidation, phenolic extraction, or unwanted microbe growth.

Winemakers often opt to make early additions of SO₂ at this point, usually right into the picking bins.

Crushing is the first process which physically breaks apart the grape berries. Crushing usually happens immediately after destemming, using a piece of equipment called either a Crusher-Stemmer or Crusher-Destemmer ( you figure it out! ).

It can be said that at the moment of crushing the winemaking process begins in earnest, since previously separate regions of the grape are mixed together. All of a sudden there is a substrate (Êgrape sugars ) for any wild microflora to start feeding on, and also the polyphenol oxidase enzymes that had been enclosed within cells are liberated.

1. Extent of crushing. In some cases ( Pinot Noir, for example ) it is appropriate to remove the stems and leave mostly whole berries This leads to a longer, slower fermentation and less extraction of bitter substances from the grapes. More common is the practice of removing stems and splitting all the berries - most red wines are made this way. For high-extract wines, such as Port, the grapes are destemmed, and the berries completely broken apart with some shearing of tissues and bruising of seeds.

2. SO₂ Addition. The main purpose of SO₂ addition at this point is to suppress growth of native yeasts and bacteria, most of which are very sensitive to sulfur dioxide. The antioxidant properties of SO₂ are not relevant at this point with red wines. SO₂ also binds readily with anthocyanin pigments in freshly crushed grapes, making them more soluble. Winemakers can also choose to make other additions at this point: acid, nutrients, and even the yeast inoculum.

3. Whole Bunch Inclusion, Stalks Return. The practice of adding a portion of whole clusters to a fermenter ( in effect bypassing the crusher ) or tossing in some stalks originated in Burgundy and is being adopted by many New World Pinot Noir producers. Intact berries undergo an intracellular, enzymatic fermentation, leading to the production of a different array of aroma compounds, and they also function to slow down the fermentation by breaking open late in the process. Stalks have lots of soluble tannins, which can bolster the total phenolic content and increase astringency in a wine that would otherwise be too soft.

4. Must chilling. In hot winemaking areas, the must can come in so warm that without chilling there would be a danger of a runaway fermentation. In practice this is rarely a problem with red wines.

5. Juice Removal ( Bleeding ). Another Burgundian practice, this involves removing a portion (up to 20%) of juice from freshly crushed grapes in order to increase the ratio of skins and seeds to juice in the remaining must. The result, obviously, is a wine with increased flavor intensity, color and tannins. Winemakers rarely have any trouble figuring out what to do with the bled juice - it is the ne plus ultra of blush and dry rosŽ production.

This is usually a bulk wine procedure. Grapes are heated by various means, resulting in the bursting of cell walls and the release of pigments into the juice. The highly colored juice that results is then fermented as if it were a white wine. The result is a soft, grapey wine for early consumption. Purple grape juice is also made by hot pressing.

Hot pressing also finds a use in some regions when grapes are heavily botrytis-infected; in this case the heat inactivates the laccase enzyme in the mold which would otherwise degrade the color. Carbonic Maceration

Not a crushing option per se - this involves placing uncrushed grapes in a container that can be sealed, purging all the air inside with carbon dioxide, then allowing the grapes to ferment enzymatically. After about 7% alcohol is produced the grapes are crushed and the rest of the fermentation proceeds in a normal fashion. This technique produces wines with a very attractive berries and spice character. It is most common in the Beaujolais region of France.

As you can imagine, there are a great many options in developing a fermentation protocol for red wines. This is but a brief overview:

1. Prefermentation Maceration, or Cold Soaking. Yet another French technique that is being adopted in the New World. Grapes are crushed into a sealable container, then chilled and left alone for up to three days before inoculation with yeast ( remember that the usual practice is to inoculate immediately after crushing ). This gives the anthocyanin pigments a chance to be leached from the skins in an aqueous environment, as opposed to one where ethanol is present. Some winemakers feel that with low-color-intensity grape varieties this technique results in a more deeply-colored, richer wine.

   Open vs. Closed Fermentation Vessel. This may seem like a trivial matter, but in fact the design of the fermentation vessel has a very powerful effect on wine style. Open fermenters have the following qualities:
   

   -they allow for dissipation of heat generated during fermentation ( + )
   -they allow a significant amount of ethanol to escape by entrainment and evaporation ( + or -, depending on the situation )
   -they provide more contact with oxygen ( + during the early stages of fermentation; potentially disastrous at completion of, and after, fermentation)
   -they are only practical for small volumes ( - )
   -they allow for gentle cap management, e.g. manually punching down the cap ( + )
   -they are not suitable for extended maceration ( - )
   

   Closed fermenters offer these qualities: -they are easily sealed ( + ) -they make warming and cooling of the must easier ( + ) -they can hold large volumes of grapes ( + ) -they are multi-purpose - can be used for storage and for white wine fermentation ( + ) -they make cap management difficult ( - ) -they have a tendency to allow the fermentation to get too hot ( - )

2. Cultured Yeast vs. Spontaneous Fermentation. This is a current hot topic with American winemakers. Adding a pure yeast culture is, of course, a comparatively recent practice, and it is one of the two or three most important factors in the dramatic improvement in wine quality over the past few decades. Nevertheless, some winemakers are finding that uninoculated fermentations can give desirable results. The main advantages of cultured yeast addition are: -a rapid onset of fermentation, allowing rapid throughput -a predictable and controllable fermentation, with little tendency to stick -the absence of undesirable aromas -efficient conversion of sugar to ethanol -the potential for producing specific, desirable aromas, mouthfeel characteristics, and color intensity

   Spontaneous fermentations offer the following advantages: -there are no costs involved -the longer time to completion, including an extended lagtime, may lead to greater extraction of color and flavor compounds -wines often display a greater degree of complexity - they are polychromatic rather than monochromatic

3. Nutrient Addition. Before fermentation begins is the best time to make additions of diammonium phosphate ( a source of nitrogen ) and vitamin mixtures.

4. Fermentation Temperature. The normal range of temperatures at which red fermentations are carried out is 18-35¡ C. Temperatures in the low end of this range make for a longer fermentation, give a wine with more straightforward fruit flavors, and prevent undue loss of alcohol. High temperatures lead to a fast, vigorous fermentation, and the wine develops more complexity and vinosity ( wine-like character ). Loss of alcohol can be a problem, and in extreme cases the fermentation can stick if temperatures reach the point where they become lethal to yeasts.

   Fermentation temperature should be matched to the desired style and to the grape variety. Pinot Noir and Cabernet usually call for elevated temperatures, at least for part of the fermentation; while soft, fruity, early release reds call for cooler temperatures. Many French-American hybrids and labrusca grapes lose their characteristic unpleasant odor when fermented warm.

5. Chaptalization. This is simply the addition of cane or beet sugar to a fermentation in order to increase the final alcohol content. There is absolutely nothing wrong with this practice unless it is overdone. It is generally practiced only in cool regions, where underripeness is a problem. As a rule of thumb, addition of 17-19 g/L of sugar leads to an increase of 1% alcohol.

6. Cap Management. During a red wine fermentation, a cap of skins floats to the surface because of the buoyant effect of carbon dioxide. Some method has to be found for resuspending the skins, soas to maximize color and flavor component extraction, and to keep the cap from getting too hot. Dried out caps also increase the likelihood of acetic acid and ethyl acetate production. The most low-tech method is to physically punch down the cap ( an open fermenter has to be used ) using a paddle-like apparatus. Alternatively, wine can be pumped from the bottom of the tank over top of the cap - this is called pumping-over or irrigating. Some wineries fit their tanks with special heading-down boards, which prevent the skins from floating to the top. Rotary fermenters are fixed with vanes, and the entire tank is rotated periodically to mix the contents.

7. Extended Maceration. Originally this was a Bordeaux practice; now it is used worldwide. It involves leaving the skins and seeds in contact with the wine after fermentation is complete, usually for two to three weeks. According to the French, pressing off should occur when the cap sinks. Leaving the wine on skins dramatically affects the wine. Color intensity diminishes slightly, while total phenolics increase. Polymerization of tannins leaves the wine richer, softer and more supple. There is some evidence that a wine treated this way has better aging capacity. Malolactic fermentation proceeds very readily in these wines.

8. Barrel Fermentation. No, it is not practical to try and get crushed grapes into and out of a bung hole. But if a red wine is pressed off before dryness, and the fermentation allowed to finish in a barrel, a new range of interesting flavors can be introduced into the wine. Barrel fermentation is very common in Australia.

This is an occasion where many elements of a wine's style can be determined. Some of the variables:

1. Timing. Pressing should occur when the winemaker determines that desirable amounts of color, flavor and tannins have been extracted. This can range from a day or two after fermentation commences to more than a month after fermentation finishes. Most commonly pressing is done at dryness.

2. Nature of the Press Cycle. This is less important in reds than whites, since the modifying of the press cycle is primarily a method for controlling extraction of phenolics.

3. Press Fractioning. This refers to separating different fractions of the pressed wine. With very tannic varieties, it is often important to exclude the high-pressure portion so it can be fined or blended away.

As you have undoubtedly learned in other sections of this course, the conversion of malic acid to lactic acid by lactic acid bacteria (LAB) in wine has a profound effect on wine. There is a reduction in acidity and rise in pH, and the wine develops a more complex aroma and mouthfeel.

Generally, the winemaker can choose whether or not to put a wine through MLF. In red wines MLF is used much more often than not, and it often occurs spontaneously. There will be more about opting not to use MLF in the section on white wines.

The timing of MLF can have a major effect on the contribution it makes to the wine's aroma and mouthfeel. Most winemakers feel that MLF occurring simultaneously with alcoholic fermentation has less of an impact than if it occurs afterwards. This can be especially important with red wines, where obvious 'buttery' character is not desirable.

Even more important is the LAB strain used. Winemakers currently have a choice of about a dozen strains, each with its own unique metabolic 'fingerprint'.

Interestingly, the vessel in which MLF occurs can influence wine aroma. Just as with wine yeast, LAB enzymes appear to react with soluble substances in oak barrels, creating a dramatically wider range of flavors in a wine than would be produced in an inert vessel. This may be one reason why French wines are often regarded as more complex than their American counterparts: traditionally MLF occurs in the spring following vintage, while the wine is in barrel.

When a wine is stored in oak barrels a great many changes take place. Most obviously, a range of aromatic compounds is extracted by the wine. White oak, properly air-dried and toasted, contains perhaps a hundred or so compounds that are either water- or ethanol-soluble. These have effects both on the aroma and on the mouthfeel of the wine.

Also, wine in barrels is exposed to small, regular amounts of oxygen. It was assumed until recently that this was from penetration of air through the pores of the wood, but that has now been shown not to be the case. What is more likely is that the act of removing the bung in order to top up the barrels or take samples exposes the wine to small amounts of air. Oxygen is generally seen as an enemy of wine; however, controlled amounts can have a beneficial effect on the polyphenolic substances in a red wine.

Lastly, wine in barrels undergoes straightforward aging reactions, most importantly the polymerization of phenolics, with an accompanying precipitation as well as a modification of tactile sensations in the wine.

A great deal of time and effort are spent by winemakers in search of the perfect barrel for their wine. To make matters worse, this perfect barrel may be different for each varietal! There are three main species of white oak ( genus quercus ) used for barrels, and perhaps 20 or so regions in the world which are used as sources of oak. Then to add more complexity to the issue there are many dozens of companies producing barrels. Each cooperage has its own specific protocol for turning hunks of trees into barrels, and results very widely, much in the same way as different winemakers approach their task in different ways. Some of the many variables are: length of time of air-drying barrel staves (Êusually 12 - 36 months ), method of heating the staves so that they can be bent ( steam or fire ), and method of toasting the inside of the barrel ( head on or off, length of time, temperature of the flame ).

Most barrels these days are made to hold 225 liters ( 60 gal ). This size is reasonably easy to move around when empty, and provides a good surface-area-to-volume ratio. A barrel of this size is capable of releasing flavors and tannins into a wine for about four or five years; after that it functions merely as a container. Most winemakers prefer to have a collection of barrels of different ages, rather than all old or all new.

Winemakers, once they have bitten the bullet and committed to a certain barrel, have lots of options when it comes to putting wine in it. Some prefer to put the wine in barrels while it still contains a lot of suspended solids ( mostly yeast ), while others prefer to settle the wine to a higher degree of clarity first. Then there is the crucial decision of how long to leave the wine in barrel. Deciding when a wine has picked up the appropriate amount of oak is both difficult and highly subjective.

Although oak barrels are essential to the production of most fine red wine styles, their high cost - $550-$600 apiece for French barrels - means that winemakers are looking for alternatives. There are many pseudo-barrel-aging products on the market, ranging from finely ground oak granules to large chips to whole staves that can be inserted in an old neutral barrel or a stainless steel tank. These usually give some, but not all, of the characters associated with genuine barrel-aging.

Generally speaking, winemakers make a small addition of SO₂ to wine after MLF has finished. However, some are now experimenting with leaving the wine without any SO₂ until the following spring. In addition to having a slight antimicrobial effect in red wines, SO₂ can affect the aging of the wine by acting as a donor of acetaldehyde, which aids in the polymerization and stabilization of anthocyanins.

The process of removing a wine from any solid material that has settled to the bottom is called racking. Racking a red wine during its time in barrel both serves to clarify a wine and also oxygenate it. Oxygenation helps to reduce the amount of H2S in the wine, and also to aid in the polymerization of phenolics. Robust, tannic red wines, especially, benefit from periodic aerobic racking.

Fining is the act of adding agents to a wine in order to selectively remove certain substances in it. With red wines, fining is usually conducted to either clarify the wine or reduce its astringency. Very few reds require bentonite fining, since any unstable proteins have had a chance to react with tannins and precipitate out. Occasionally, a red wine with obvious H2S will be fined with a small amount of copper sulfate.

After a red wine has been through its pre-bottling aging period, it occasionally needs to have its flavor profile 'touched up'. This can involve acid adjustment, either up or down; dealcoholization; or in the case of some inexpensive wines, addition of sugar.

Almost all wines are blends of wines from different lots, barrels, winemaking regimens or grape varieties. Ideally, the best wine is from all the wines bulked together, but this is often not the case. In the months proceeding bottling winemakers spend a great deal of time experimenting with different blends. The French even have a word for the creation of blended wines: assemblage. Many high quality red wines, especially those from the New World, are blends of dozens of different wines.

Chilling a wine in order to cause the precipitation of potassium bitartrate in advance of bottling is often, but not always, carried out with red wines. The drawback is that inevitably a small amount of anthocyanins are also removed. A nice trick with cold stabilization is that with wines below pH 3.65, it results in a decrease in pH and titratable acidity.

Filtration of reds can range from none at all to sterile membrane filtration. Each approach has its pros and cons. Minimal filtration is currently in vogue with California red winemakers, and can work well if the wine is absolutely microbiologically stable. Proponents feel that any filtration inevitably removes color and flavor from the wine. Tight filtration gives the winemaker great peace of mind by removing all microorganisms from the wine. Filtration can be accomplished either with diatomaceous earth, cellulose pads, or membranes.

When a wine is finally ready for bottling, a number of factors have to considered. In fact, many large wineries have a quality control staff to oversee the bottling of wines. In addition to any final filtration, factors to consider are the temperature of the wine, the dissolved gas content, the free and total SO₂ levels, rinsing and inert gas sparging of the bottles, and the type of closure used.

The bottle aging of red wines before release is becoming less and less common, for economic reasons. Still, some wineries choose to delay the release of wines so that they 'show' well when they hit the shelves.