On a purely scientific level, wine is made by the yeasts feeding on the sugars which occur naturally in grapes and converting them into alcohol. This is called fermentation.
But while the science might sound straightforward, the process of getting from a grape in the vineyard to a glass on the table is often a long one, with multiple steps and lots of subtle but important decisions to be made along the way.
This article focuses on the process of making red wine. But we also have an article on How White Wine is Made. The processes are similar, so don’t be surprised if there is some overlap in the two articles. And you can also read about How Cava is Made.
So, let’s begin in the vineyard where the grapes are being harvested. This is a critical time for winemakers. The grapes have to be picked at just the right moment - too early and they won’t have ripened enough, meaning there won’t be enough naturally occurring sugar in the grapes before they are fermented, and the final wine may end up being too acidic. But picking late is risky too; over-ripe grapes have too much sugar which can make for very alcoholic wines with low acidity – what the experts call ¨flabby¨ wines. So, the oenologist’s decision as to when to pick is vital.
Once they give the go ahead it’s full steam ahead to harvest all the grapes as quickly as possible – either by hand or with machines depending on the size and layout of the vineyards. In places like Ribeira Sacra for example, vineyards cling to the steep sloping banks of the Xil and Miño rivers, and machine harvesting is impossible. Whereas in parts of Rioja, La Mancha or Rueda (to name just a few) you’ll find larger vineyards on relatively flat land where grape harvesters – tall, tractor-like machines which can straddle the vine rows and pluck the grapes off automatically - can whizz through the harvest in much less time.
Once harvested, the grapes are usually loaded on to trailers and driven by tractor to the winery where we can start getting to work on them. In very hot climates where high temperatures risk spoiling the fruit before it reaches the winery, grapes are sometimes harvested at night when it is cooler or kept refrigerated between vineyard and winery.
Once the grapes arrive at the winery they go on to the sorting table, a kind of mini conveyor belt like at the supermarket where dexterous hands sift out any rotten berries or leaves so you are just left with healthy bunches of grapes.
Now comes another decision moment – destem and ferment just the fruit or keep all the grapes together on the stem for a so-called whole bunch fermentation?
The practice of whole-bunch fermentation is becoming more common in some parts of the world. Keeping the grapes and juice in contact with the stems during fermentation helps leech a little more tannin into the wine which can give it a bit more astringency and increase its ageing potential. Proponents argue that keeping the stems in can also add aroma, complexity and freshness to the wine - a bonus in hotter climates - while others are wary of the ¨green¨ aromas that underripe stems can give the wine.
That decided, the grapes are now fed through a crusher to help open up the grapes and expose the flesh inside so the yeasts can do their work. This gives us the souply cocktail of juice, skins, and flesh of the grapes, known as ‘must’ or mosto in Spanish. The crusher´s work is done, the mosto then goes into the fermentation tank, usually made of stainless steel.
Now red wine gets its colour, and a lot of its characteristics from the grape skins themselves – remember the flesh of all grapes is essentially colourless - so it’s important that the juice spends time in contact with them. Contact between skins and juice is called maceration. As we’ll see later, maceration takes place while the wine is fermenting, but winemakers can also choose to start the maceration process before, letting the grapes sit in the fermentation tank at a cool temperature for a short period – anywhere from a few hours to a couple of days - in order to extract more colour, flavour and tannin from the skins.
(At this point some wineries will add sulphur dioxide to help stop the grapes from spoiling. There’s a lot of debate over the use of sulphur dioxide, and a lot of winemakers go to great lengths to show that they don’t use sulphurs in their winemaking. But the truth is that it can ensure the health of an entire batch (which can mean the difference between a winery surviving or going under) and the amounts allowed by EU directives are well-below the threshold to worry about.)
Now it is time for the yeasts to do their work and fermentation to begin. Again, the winemaker has a choice. He or she can add cultured yeast to the must, a shop-bought variety if you like which he or she has bought in or developed in-house. Alternatively, they can rely on the native or indigenous yeasts that occur naturally in the winery and the vineyard (eg on the skin of the grape itself). With the must inside the fermentation tank, the winemaker needs to slowly increase the temperature, prodding the yeasts into life so that they can begin converting the naturally occurring sugars in the must into alcohol. For red wine, the optimum temperature is generally between 25 – 30ºC, and the fermentation process itself usually lasts between 5-7 days.
Now because the red wine must is a mixture of solids and liquid, over the course of fermentation as carbon dioxide is produced the solids tend to float up to the surface and form a cap. But as we saw earlier, red wine gets its colour and a lot of its flavour characteristics through maceration – contact between the liquid and the skins. So, to encourage that contact winemakers will regularly mix the floating solids back in with the liquid. in one of two ways – punching down or pumping over.
Punching down means physically pushing the quite solid cap sitting on top of the fermenting must back down into the liquid and mixing it all together again. This is usually done using a long pole with a flat disc at the end. The alternative, pumping over, involves pumping off the must from the bottom of the fermentation tank and spraying it back in at the top to wet the cap and encourage that all important contact once more. The frequency with which punching down or pumping over happens depends on the result the oenologist is looking for, as well as the overall fermentation time of a particular wine. But it can be up to several times a day – so the winemaking team are kept busy while the wine is fermenting.
Fermentation continues for as long as there are sugars for the yeast to feed on and the temperature is at the right level. In some wineries, fermentation is allowed to continue until it reaches its natural conclusion. But other wine makers control the process more directly by monitoring sugar levels in the fermenting wine. When the sugar and alcohol content reach the desired levels, they then lower the temperatures to bring the fermentation to a controlled end.
At this point in the process, the now fermented wine is drained off and put into tanks to settle. Sometimes, the remaining solids are given a pressing at this stage too to extract the last of the fermented juice which can then be added to the rest. At this stage, different materials can be used. Tanks may be made of different materials like stainless steel, wood, concrete or clay. And each material will impart different characteristics to the final wine (or, in the case of inert stainless steel, ensure no unwanted characteristics are imparted).
Another process which usually takes place in red wines at this point is malolactic fermentation, or plain malo as winemakers sometimes call it for short. This is a natural process in red wine where bacteria convert malic acid, which is quite sharp, into lactic acid, which is softer and more buttery (it’s the acid found in dairy products). This makes the final wine softer and rounder in the mouth. Malolactic fermentation is a natural process, but some winemakers will intervene to control how much takes place – either by using bacteria to actively encourage the fermentation or by controlling temperatures to prevent too much malolactic fermentation from occurring, thereby retaining a wine’s natural acidity.
We are now getting to the final stages. We have a fermented liquid, malolactic fermentation is out of the way, and the solids have mostly settled out of the wine. But there may still some steps to take – most notably blending and ageing.
If winemakers are producing wines from a blend of grapes – or in some cases the same grapes grown in different plots, they will often ferment them separately and then blend them together to form the final wine. This process is known rather grandly as assemblage, or ensamblaje in Spanish.
Once blending is out of the way, the winemaker needs to decide if his or her wine is going to be aged for a period of time before it goes on sale. If so, at this point it’s often racked off into wooden barrels – or, increasingly, other other materials like concrete or clay – and allowed to sit and age peacefully for the requisite period of time (you can find out more about ageing in our article here).
Whether aged or not, the wine is now ready to be put into bottles. But before that is done it needs a final process of clarification to remove any last remaining particles and leave us with a lovely clear liquid. Left to its own devices, the wine would actually clear by itself naturally over time, but sometimes winemakers need to speed up the process. This is done in two ways – fining and filtering. Fining means the addition of special fining agents to help coagulate and absorb the microscopic particles in the wine. Traditionally many of these agents were derived from milk, egg white or even, in the case of isinglass, the bladders of fish! These are all still used, but in addition nowadays there are other vegetarian options available too. Filtering is, as you would imagine, the process of passing the wine through a series of filters to take every last solid out of the final liquid.
Increasingly winemakers - particularly so-called natural winemakers - opt for a ¨minimum intervention approach¨ in order to highlight the natural characteristics of the wine and that can mean skipping the fining and filtering stage altogether. This can mean that their wines have a slightly cloudy aspect to them. We are used to wines being clear so can sometimes be put off by that, but it’s by no means and a bad thing and unclear wine does not mean bad wine.
Finally, we get to the bottling stage. There isn’t much to be said for this – wine goes into a bottle and a cork gets added. But it is important to note that once it’s in the bottle wine continues to evolve, taking on what are known as tertiary aromas associated with ageing (as opposed to primary aromas from the vineyard, or secondary aromas from the winemaking process itself). To help this process along, a lot of wineries will keep their bottled wine in their cellars for some time before releasing it onto the market. In most cases this is just a short time to let the wine rest and the flavours combine fully. But in others wine can be bottle-aged for several years until they are in optimum condition for sale.
So, there we have it. How red wine is made from start to finish. If you’re interested to see the differences between red and white wine production, you can dive into our sister article on how white wine is made. Otherwise, we suggest diving into a glass of red and savour the end product of all that hard work.