Human intervention plays a big role in determining the style of a wine. Through the steps of the winemaking process, I’ll examine the major decisions involved
When I began my journey into wine, I was amazed to discover that every decision in the winemaking process affects the style, taste and even its price. I like an analytical approach (another way to say I’m a nerd!), therefore I enjoyed studying all the facets and nuances of winemaking.
Maybe you just like drinking wine and you cannot see why you should be be bothered with the technicalities behind its production. Nonetheless, knowing the basics of the winemaking process can help you predict how a wine will taste and why.
The elements that affect wine style can be roughly divided into two macro-categories:
- Nature: the factors defining the vine growing environment
- Humans: viticultural and winemaking decisions
In a previous article I covered the natural elements affecting wine style. Here, I will outline the human-based decisions and their impact. Since there is a lot to cover, I will divide this article into two parts.
The human factors influencing the nature and the taste of a wine are countless. Although none of these factors are trivial, I will focus on the most important.
Winemaking
Let’s start with a basic definition of winemaking by Wikipedia:
Winemaking is the production of wine, starting with the selection of the fruit, its fermentation into alcohol, and the bottling of the finished liquid.
Definition of “winemaking” according to Wikipedia
In simple terms, winemaking is a process. It starts with fruit and ends with wine in a bottle. However, at the same time, winemaking is more complex than the Wikipedia definition.
The only way to fully understand the nuances of wine is to accept it is a multifaceted phenomenon. Therein lies its beauty. The good news is that even complex concepts, like winemaking, can be broken down into bite-sized chunks and fully understood.
The winemaking process with an infographic
The following infographic details the major steps of winemaking.
Further detail about the steps highlighted in the infographic to follow.
Harvest
In the majority of the resources on the topic, you won’t find harvest as part of the winemaking process. I think that’s a big mistake. When to pick the grapes is the most sensitive decision wine growers have to make in the entire vineyard annual cycle.
Timing is essential, and it does greatly influence the wine style. If a winemaker wants a riper, fruiter wine – they will pick later rather than earlier. In a later harvest, grapes have higher sugar content, greater concentration of flavours and alcohol. An early harvest ensures there is less ripeness and alcohol in the wine but more acidity and variety in its aromatic profile. Of course the key in wine, like in life, is balance. Therefore most winemakers will opt for a compromise between ripeness of fruit and acidity as their aim is to balance all the structural components in the juice.
Another important decision is the method of harvesting the grapes. The options available are manual or mechanised picking. The decision really depends on a number of factors. For example, the availability (and cost) of labour, the topography of the vineyard, weather conditions and the winemaker’s preferences.
If the harvest is mechanised, machinery is employed to shake the vines and collect fallen grapes. This method is less selective as it doesn’t differentiate between suitable and unsuitable fruit. Its main advantage is speed, so mechanised harvest is the best choice if timing is a constraint. For example, to minimise oxidation or if bad weather is approaching and you want to bring the grapes to the winery as soon as possible.
Mechanisation is not always possible. Where steep slopes are present (such as Mosel in Germany, Northern Rhone in France or Douro in Portugal) this option is just not available.
Hand harvesting (also known as “manual harvesting”) employs human labour to hand pick individual bunches of grapes. This process is time consuming, labour-intensive and usually more expensive (except where labour costs are less than machinery adoption). However, hand harvesting allows better grape selection as workers can be trained to reject less than optimal bunches.
For this reason, hand picking is essential for certain styles of wine which require only grapes picked with the correct level of ripeness. An example where hand-picking is the only viable option are wines made from grapes affected by noble rot.
In general, hand-picking causes less damage to vines. Unlike machine harvesting, vines are not violently shaken so they are less stressed. In addition, the soil is not overly compacted by heavy machinery going up and down the vineyard. However, recent improvements in technology ensures that premium wine can be obtained by both harvesting methods, mechanised and manual.
Grape sorting and destemming
As soon as the grapes arrive in the winery, they are subjected to some preliminary activities.
First, the winegrower may choose for the grapes to be sorted. If they are sorted, human workers eliminate damaged or unsuitable grapes as well as the so-called “MOB” (Material Other than Grapes). MOB is a fancy term for all the rubbish can be unintentionally grabbed during the picking. Examples include: insects, small animals, leaves, garbage.
Grape sorting is a process usually reserved for premium wines. Spoiler alert for the consumer of the £5 bottles: the raw material of your wine might contain some MOB! Don’t worry. What doesn’t kill you makes you stronger!
Next, the grapes are destemmed. Destemming is the process that separates vine stems from the actual grapes. Destemming is an optional step usually done by machinery which crushes the grape at the same time (see below). Please note that with machine harvest, grapes arrive at the winery already destemmed – so further destemming is unnecessary.
Some winemakers allow whole bunches (grapes attached to their original stems) to ferment with destemmed berries. This technique, now popular with some premium pinot noir, increases the aromatic profile and tannin levels of the resulting wine (vine stems contain a lot of tannins). Whole bunches are not usually included in the fermentation process of grape varieties which are naturally high in tannins or where stems are bitter (for example cabernet sauvignon).
Crushing
Another optional process (it is not carried for whole bunches or carbonic maceration), crushing breaks the skins of the berries, liberating a liquid often called “free run juice”. This liquid is usually of the highest quality and can be fermented, matured separately, or included in the blend later on.
While crushing is usually a mechanised process, it can also be done by human feet. Crushing should be as gentle as possible, to avoid damaging pips or stems. If these are crushed, they may release bitter flavours, damaging the overall wine profile.
As mentioned above, the key is balance. Too little crushing will lead to an insufficient aroma extraction, while too much extraction will result in astringent and bitter aromas.
Pre-fermentation maceration
After the grapes are sorted, destemmed and crushed, they are ready to be fermented. Before fermentation starts, the winemaker may choose to add an additional step, that is to leave the skins in contact with the must (crushed fruit and skin). In red wines, the practice is called “pre-fermentation maceration” or “cold soaking”, in whites, it is normally referred to as “skin contact”. If temperatures are 6-7°C or more, it may become necessary for the winemaker to cool the must to prevent fermentation kicking in too early.
Winemakers use pre-fermentation maceration to increase the complexity and enrich the aromatic profile of a wine. The inclusion of the skins increases the transfer of colour and flavour compounds to the wine. However, it has no effect on tannin extraction.
It’s easy to discern the whites that have had some skin contact. The colour of these whites are normally more intense and the nose reveals savoury and natural notes. When skin contact is prolonged, colours continue to be extracted all the way into the first stages of fermentation. This is how orange wine is usually made.
Pressing
Pressing is probably the most crucial activity that occurs before fermentation. Practically speaking, pressing separates the liquid from the solid constituents (the pips, skin and fibres that make up the grape). Pressing is achieved by some sort of compression. The traditional vertical presses are filled from above and have a plate that progressively squeezes the must. More modern presses use other approaches, like inflatable rubber membranes or stainless cylinders.
Pressing is different from crushing and it is important that it is not confused. In crushing, the grape skin is pierced but pressure is applied. Whereas pressing is the actual compression of must. In both processes, winemakers should avoid damaging the solid constituents of the must in order to avoid bitter and astringent flavours seeping into the wine. With pressing, such damage is avoided by the use of gentle and controllable pressure. In Champagne production, pressing is one of the most delicate phases – pressure is meticulously controlled and highly regulated under the appellations rules.
While squeezing the must, liquid is collected at each stage and passed through other winemaking steps. The liquids released at different stages of pressing are not the same. Each pressing stage is is called a fraction. Winemakers usually separate the liquids of produced during different fractions. Fractions can either be blended together or vinified separately in different ways (for example, one fraction may see oak while others may not). Generally, the juices coming through at the start of pressing are lighter in tannins and have bright pure fruity flavours. The liquid produced towards the end of the pressing tend to be more tannic and astringent.
The point at which pressing occurs is one of the defining differences between white and red winemaking. For white wines, pressing takes place before fermentation begins; while reds, its after. White wines are fermented off the skin, therefore they don’t display red/black pigments and have a significantly lower amount of tannins. As for reds, fermentation occurs in a must which contains skin, pips and other solid parts. That’s why reds differ so much from whites in terms of color and tannin content. Colour and tannins are extracted from the skin during fermentation.
Clarification
Unsurprisingly, most people like the wine they drink to be clear and free from sediment or insoluble particles. Clarification techniques allow winemakers to get rid of these pesky solids from their wines. For some of these techniques are controversial. There are winemakers who swear the removal of these particles strip away the true character and flavours of a wine. Therefore the winemaker’s preferences determine the type and extent clarification techniques are used in the wine.
Clarification techniques can be roughly grouped into three categories. Racking, fining and filtration.
Racking is the gentlest and least intrusive of the clarification method. For this reason, it’s the only clarification technique used for certain types of wine. The liquid (containing solid particles) is left in a vessel for some time. Thanks to gravity, the insoluble matter gradually settles at the bottom of the container. The liquid is then pumped into a different vessel, leaving the solid particles behind at the bottom of the original container. Repeated racking, from one vessel to another, allow the winemaker to get rid of most of these particles.
Fining is the addition of certain substances (albumine, gelatine, bentonite, carbon) to the wine. These substances (called “fining agents”) are capable of bonding with the particles floating in the wine, forming bigger particles. The larger particles formed during the fining process are subsequently removed by filtration.
Filtration is the physical process of removing particles from the liquid. Wine is passed through either a sieve or a filter with holes or pores small enough to trap the solids while the liquid is collected separately.
Fining and filtration are regarded as by winemakers as an aggressive clarification method. As a result, some winemakers refused to use such techniques. Wine made by such winemakers will usually bear the words “unfiltered” or something similar on the wine label. Wines that have not been fined or filtered may appear slightly more hazy to the eye, but there is no detriment to the quality and aromatic profile of the wine. I personally find a lot of unfiltered wines to be very interesting (and I mean that in a good way!).
Clarification techniques can be adopted at different stages of the winemaking process. Often white wines undergo some sort of racking procedure before the start of fermentation. This is to avoid skin and other solid particles remaining in the must during fermentation. If such particles are not removed, this can result in the wine developing undesirable savoury aromas.
After fermentation, racking is used in white wines, to separate the liquid from the lees (dead yeast cells that remain after fermentation has completed). However, some winemakers, favour contact with lees as it gives the wine more body and structure – therefore racking is not carried out at this stage.
Winemakers also use clarification processes used just before the wine is bottled. This is to ensure that the liquid is packaged clear without solid matter that may be off-putting to customers. At this stage, a more fine-grained filtration may also be used to ensure microbiological stability. In other words, yeasts and bacteria are filtered out from the wine to avoid it spoiling later when these bottles are on shop shelves.
Alcoholic fermentation
Alcoholic fermentation is the basis for the manufacturing of all alcoholic beverages – and wine is no different. This complex biochemical process converts sugar into ethanol (alcohol) and carbon dioxide (CO2), thanks to the action of yeasts. The reaction produces other byproducts, such as heat and chemical compounds that ultimately determine the flavours in wine.
Without the winemakers intervention, alcoholic fermentation would continue until all the sugar in the must is completely converted into alcohol – obtaining dry wine. However, there are a number of ways that a winemaker can stop alcoholic fermentation early. These include: adding spirit or sulphur dioxide to the must or filtering out the remaining yeasts. All these methods result in some sugar being left in the wine – also known as residual sugars. Some sweet wines (but not all) are produced by the winemakers leaving some unfermented residual sugars.
Winemakers control alcoholic fermentation in two ways: yeast and temperature. Yeasts are microscopic fungi that, in the absence of oxygen, feed on sugar and produce alcohol. Yeasts are literally everywhere and the types are countless. From a winemaking standpoint, we are interested in a specific species of yeasts called Saccharomyces cerevisiae. These yeasts are alcohol and sulphur dioxide tolerant, fitting perfectly into the job of wine fermentation.
When it comes to fermentation, winemakers have two choices. They can use the yeasts naturally present in the surrounding environment (in the winery and on the grape bloom) or commercially cultivated yeasts.
Wild (or spontaneous) fermentation involves ambient yeasts. These yeasts produce more aromatic wine with interesting flavours and greater complexity. Nonetheless, winemakers have less control of wild yeasts. They are inconsistent and unpredictable which can be a problem in large-scale wine production.
The other option is to use commercially cultivated yeasts. These yeasts have a narrower aromatic profile but are easily controlled. They consistently produce predictable attractive flavours.
The second way winemakers can influence fermentation is through temperature control. Alcoholic fermentation does not take place if the temperature is below 5°C or above 35°C. Lower temperatures during fermentation favour the development of fruity flavours. They also reduce the loss of more volatile flavours such as floral and other subtle notes.
Higher temperatures during fermentation are necessary for the extraction of color and tannins.
This is why white wines ferment at a significantly lower temperature when compared to red wines. In white wine fermentation temperatures range from 12°C – 22°C. While temperatures in the fermentation of red wines range from, 20°C – 32°C.
Throughout the fermentation process, temperature is constantly monitored. The ease in which temperature can be controlled is one of the major advantages of modern winemaking. It is also one of the substantive reasons for the giant leap in wine quality over the last 20 years.
Alcoholic fermentation of the must can take place in different types of vessels: oak, concrete, stainless steel vats. However oak is never used for red wine fermentation and this is for a practical reason. Oak barrels are sealed, while in red wine fermentation the vessels need to be open.
During fermentation of red wine, the must contains pulp, skin and other solid compounds (collectively known as cap). The cap, if left alone, would just float on top of the fermenting liquid. This would lead to a poor extraction of colour and tannins. Different cap management techniques exist all with the aim of improving the contact between the cap and juice. Since these cap management techniques require the cap to be stirred, they make oak barrels (that are closed) impractical vessels for the purpose.
In addition, temperature control with oak vessels is inefficient due to the lack of embedded instruments. Therefore oak is used mainly for the fermentation of white wine, usually when the winemaker wants it to have toasty flavours, more body and some degree of oxidation.
Concrete and stainless steel vats are inert vessels. They don’t impart any aromas. Consequently, they favour a more reductive (as opposed to oxidised) style of winemaking and they allow easier temperature control. I will discuss vessels in more detail in the blending section of my next article of this series.
Afterword
Enough for this week folk! The magic of alcohol fermentation ends the first part of this article. In the second part, I will cover the remaining steps of the winemaking process – post-fermentation, maturation, blending and finally the release of our beloved bottles.
Until then, try to find out more about the winemaking process of your favourite wines. Talk to your wine guru, advisor, or shop assistant. Visit the wine producer’s website or ask google. How is the harvest performed? Is the wine clarified? Is is subject to some maceration? The answers to these questions will allow you to connect the dots between winemaking techniques and wine styles or tastes.
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