Those of us who live in wine regions will know what vignerons, or grape-growers, do.
We see them pruning the vines, driving their tractors and harvesting their grapes. But growing grapes is only half the story of wine.
The other part is the transformation of grapes into wine. It takes place behind the closed doors of cellars, out of view of the locals. What are those winemakers – the vinificateurs and cavistes – actually doing?
Harvest is the busiest time in the cellar and most winemakers will hire extra staff to carry out many of the more laborious tasks, much of which involves cleaning equipment. There is a saying that winemaking is 90% cleaning up and 10% not screwing up.
It’s not quite true; winemaking is about making lots of decisions that will influence the style and quality of the wine.
Read more: ‘Why this was my most challenging harvest as a winemaker in France’
Different grape pressing process for white, rosé and red wines
When grapes arrive at the winery, whether hand-picked or machine harvested, they are usually put through a machine called a de-stemmer (égrappoir in French) which removes the grapes from their bunches.
Some high-quality wineries will have a sorting table where bunches or even individual grapes are inspected and rejected if they are unripe, mouldy or too raisined.
After de-stemming and sorting, the grapes may be fed through a crusher, which doesn’t really crush the grapes, it just breaks the skins to allow the juice to flow out.
If the grapes are destined for white or rosé wine, they will next be transferred to a press, either by pump or conveyor belt.
Most modern presses are programmable and automatic. All the winemaker needs to do is select the appropriate programme for the grapes and style of wine and then be on hand to pump pressed juice into tanks and make sure nothing goes wrong.
To make red wine, the skins are fermented along with the juice, so no pressing takes place at this stage.
The grapes are put straight into tanks, usually after de-stemming and crushing but sometimes as whole bunches.
All of this equipment – the de-stemmer, the crusher, the press, the pumps, hoses and tanks – all need to be cleaned ready for the next batch of grapes.
In a winery that processes a lot of vineyards, that may mean working around the clock in shifts to keep up with the fruit coming in.
Read more: A French grape variety guide by winemaking region
First decisions are about sulfites, enzymes and tartaric acid
At this stage, the first winemaking decisions are made. Does the juice need sulfites adding to prevent oxidation or clean up damaged fruit? Should enzymes be used to get more clear juice from the pressed fruit?
In hot regions, winemakers are permitted to add a small amount of tartaric acid to their must (le moût) if required, while in cool ones they may choose to add sugar to make up for lack of ripeness.
White and rosé juice needs to be settled overnight at a low temperature to clarify it and rack it off the heavy solids which fall to the bottom of the tank.
The next day it will be pumped to another tank or perhaps barrels, ready to be fermented.
Red juice may be kept under refrigeration for up to a week, protected under a blanket of carbon-dioxide gas, in order to extract colour from the skins without too much tannin.
Deciding which yeast to use
Once ready to ferment, the winemaker has to make decisions about what kind of yeast to use.
There are many commercial yeast strains on the market which emphasise or reduce various characters in the wine or are more suited to the sugar or acid level of the juice.
The winemaker may also choose not to add any commercial yeast and rely on the wild yeast growing on the skins of the grapes.
Fermentation temperatures impacts final flavour
The temperature at which fermentation takes place can have quite a dramatic impact on the resulting flavour.
Large modern wineries are equipped with temperature monitors and automated refrigeration systems that allow the winemaker to programme the temperatures of each tank as they desire.
In more artisanal wineries, keeping the fermentation temperatures in the desired range requires regular checking and adjusting of the refrigeration equipment.
Most important decision in making red wine
The fermenting red wines need to be ‘macerated’ on their skins to extract the desired amount of tannin, colour and flavour.
This is one of the most important decisions in red wine making. It involves regular pumping of the juice from the bottom of the tank onto the top of the skins or punching the skins down into the juice using large plungers.
Either process is time-consuming and needs to be done up to three times a day for each tank.
Read more: Tannins can make red wine undrinkable or delicious – what are they?
Daily checks to avoid dreaded ‘stuck-fermentation’
As well as processing the incoming fruit, keeping all the equipment clean, monitoring the fermentation and carrying out the maceration routine, the winemaker needs to keep daily records on all the wines in the cellar.
This will involve taking samples and measuring the density, sugar content, acidity and possibly other things to help make decisions about additions and procedures to keep the ferments on track and avoid any problems such as the development of off-flavours like acetone, burnt-rubber, rotten eggs or vinegary smells.
Above all, they need to make sure that the yeast is kept alive long enough to convert all the grape sugar into alcohol and avoid the dreaded stuck-fermentation that can result in wines refermenting and exploding in the bottle.
Small family wineries, without a university-trained winemaker, will probably make use of an oenologist from a local laboratory to do most of the analysis and make recommendations on actions to be taken.
Decide if wine should go through malolactic fermentation
After the primary fermentations are complete, the work is not finished.
The skins of the red wines need to be dug out of the tanks and then pressed. The red wine then needs to settle in the tank before it is racked off again to remove the yeasty sediment known as lees.
Winemakers can also choose to put the wine through malolactic fermentation, which converts crisp malic acid into softer lactic acid – a process that can take anything from a few days to several months.
Harvest work is not finished once last grape is picked
Finally, the wines are transferred to their chosen vessel to allow them to mature for several months or years. That may be a stainless steel tank for fresh white or rosé wine or a selection of oak barrels for red wines and richer whites.
All the harvest equipment needs to be thoroughly cleaned to remove tartrate deposits and put away for next year.
Once the finished wines are in their chosen resting places, the winemaker can take a well-deserved break. It always amuses me when my neighbouring vignerons, who take their grapes to the local cave cooperative, assume that the harvest work is all over once their last grapes are picked.
Winemaking may take place behind closed doors but the harvest isn’t finished until about two months after the grape growers have been on their holidays.
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