The colour of a wine can tell you much about it, but sometimes all is not what it seems.
Decades ago it was quite normal for a Burgundy producer to add a good slug of wine from a warmer part of the world to make up for any deficiency in their product. In theory this shouldn’t happen any more, and better vineyard practices and winemaking skills have improved the wines. There are rumours of this sort of practice still happening in some regions; and in some parts of the world the geographic boundaries are so large that blending is normal practice.
What gives a wine its colour?
The colour comes mainly from the grape skins. A classic example of this is the Pinot Noir grape variety. It normally makes red wine, but the pulp in the centre of the grape is white, so, if you gently press the grapes, and ferment the juice you get a white wine, as in Blanc de Noir Champagnes.
I’ll exclude fortified wines.
White – wine made by pressing grapes, and fermenting the juice without skin contact.
Orange – wine made from white grapes, but where the skin is in contact with the juice during fermentation. This was very unusual, but is becoming more popular.
Rosé – wine made from red grapes, where the grape skins are left in contact with the juice for a short period to impart some colour.
Red – where the grape skins are left in contact with the juice throughout fermentation. The colour can vary from a pale garnet to an inky impenetrable purple.
Which other factors influence the colour?
Acidity. Usually expressed as the pH. The acidity decreases as a wine ages.
Sulphites. These are added as an anti-oxidation and to kill off bacteria, but they also change the colour of a wine.
Ageing. The chemical reactions in a wine cause white wines to become darker in colour as they age, and red wines to become paler. They all tend towards brown in the end.
Oak barrels. Some air reaches the wine whilst it is an oak barrel, and this can affect the colour, as can some chemicals leached from the oak.
Wine additives which influence colour
In addition, or instead of, blending wine from outside the region, some winemakers will add food colouring. The most honest of these are at least grape-derived, an example being ‘Mega Purple’. They are concentrates where a little goes a long way, and some change the taste as well as the colour.
It is also possible to remove colour by using activated charcoal.
There are two ways of looking at the manipulation of wine:-
The wine reflects the area that it comes from, often referred to as terroir, and also the winemaker’s skill. The addition of wine from outside the area, or wine concentrate, masks the individuality of the wine and so detracts from it.
The winemaker aims to produce a consistent product every year, and that additives which achieve that are entirely justified. Cynics might suggest that they simply make up for poor winemaking. It should be said that the blending techniques used in Champagne to achieve a standard non-vintage wine are an honest way to achieve a consistent product.
Sugar plays a vital role in the wine in your glass, even if you can’t taste it directly.
What is sugar?
Sugar is the name given to a wide range of carbohydrates, but only the simpler ones are sweet.
Glucose – one of the main products of photosynthesis in a plant, making up about 50% of sugars in ripe grapes. It is one of the three simplest types of sugar, known as monosaccharides. This is absorbed straight into the bloodstream during digestion.
Fructose – another monosaccharide, making up the other 50% of sugars in ripe grapes. It too is absorbed straight into the bloodstream during digestion.
Sucrose – the type of sugar you put in your tea, is typically produced from sugar cane or sugar beet, and very little is found in ripe wine grapes. Sucrose is in fact a combination of glucose and fructose.
Production of sugar in wine grapes
There is very little sugar in a grape until véraison, when the grape starts to change colour and ripen. Acidity decreases, and sugar contents rise, see the graph in a previous post. The trick is to get the correct balance between the two. Sugar concentrations in ripe grapes can easily achieve 20%.
Adding sugar manually
Before fermentation – sugar in grapes is converted to alcohol during fermentation, but if the grapes aren’t ripe enough, sugar may be added to artificially increase the alcohol content. A process known as chaptalisation. If this is done carelessly, there isn’t enough fruit in the wine to balance the relatively high alcohol. This practice is banned in many wine regions.
Adding two lots of sugar – Champagne manufacture involves adding sugar and yeast to produce bubbles in the bottle, and then sugar at the end to take the edge off the acidity.
Fermentation Yeasts turn the simpler sugars into alcohol plus carbon dioxide, but many other reactions also happen, and some of the complex sugars remain.
Effect of residual sugar in wine
Tasting threshold – for most people this is around 1% sugar content, but those who are particularly sensitive can detect 0.2%. A dry wine which is fully fermented out will have a sugar content of < 1.5 gm/litre, which is not detectable.
Balancing other tastes – sweetness balances acid and bitter tastes, making them less harsh.
Provides food for microbes – residual sugar in wine encourages bacterial growth unless it is properly protected. Sulphur dioxide is important here, see previous post.
In most wines, sugar just has a fleeting presence for a short while before the grapes are picked. It is created by photosynthesis, and consumed by fermentation.
Yeasts are fungi, which play a vital role in wine production. The number of different species runs into tens or even hundreds of thousands, no one is quite sure. More than one may be used in fermenting the grapes, and this has a big influence on the wine produced. Yeasts produce aromatic compounds as well as alcohol and carbon dioxide.
What yeasts need to make them work
Yeasts need the right conditions to work their magic during wine fermentation:-
Temperature. They operate in a temperature range. Too low, and yeasts don’t function, too high and they are killed off. The grape juice may be actively heated or cooled to achieve this.
Nutrients.Sugar is the main one, but you need a source of nitrogen, which is provided by amino acids. Winemakers may add selected nutrients.
Alcohol level. Different yeasts work in different ranges of alcohol content.
Winemakers split yeasts into two main categories
‘Natural’ or ‘wild’ yeasts. These are the yeasts which are present in the vineyard, and stick to the grape skins. They are also on the wine equipment. These indigenous yeasts give the wine a local character, a sense of place. The term ‘terroir’ is often used to express this.
Cultured yeasts. These are developed to introduce particular characteristics to the wine, or to make fermentation more reliable. Usually, the indigenous bugs will be killed off with sulphur dioxide, and then the grape must/juice will be inoculated with the cultured yeast.
What can go wrong with a ‘wild yeast fermentation’
Problems with starting the fermentation. The grape must/juice will contain a range of bacteria as well as yeasts, and these compete for the nutrients. You may end up with acetic acid (vinegar) rather than alcohol.
Inconsistency. A number of different yeasts may be involved during a fermentation, with some dying off at quite low alcohol levels, and others taking over. If a different yeast takes over, you can end up with a different wine than you anticipated.
There is no right or wrong answer about the use of wild yeasts, it rather depends on the market you are aiming at. Cultured yeasts will help to produce a consistent product, which is going to appeal to the big brands. Small producers may well enjoy the variability.
Sulphite additions to food and wine have become a big issue. However, the sulphites, and the sulphur dioxide that they produce have real benefits.
Why is the term sulphite used? Sulphur dioxide is sometimes injected as a gas, but solid sulphite granules are usually added instead. The acid in wine rapidly splits this up to produce sulphur dioxide which actually does the work.
Sulphur dioxide occurs naturally in wine
This may seem unlikely, but fermentation of grapes produces sulphur dioxide without any help from humans. The amount depends on the the yeasts that are used, but it is a ‘natural’ product.
Why are sulphites added to wine? There are two main benefits:-
Antioxidant – if wine is exposed to air, the alcohol is quickly oxidised to acetic acid (vinegar). So, nature’s natural tendency needs to be moderated, if we are to drink the wine before it goes off. Sulphur dioxide attacks the chemicals which would otherwise produce vinegar. This is less of an issue for red wines which have their own antioxidants.
Antimicrobial – wine contains yeasts and bacteria. The magic molecule prevents these from multiplying and spoiling the wine.
Which wines have the most sulphur dioxide? SO2 binds with many compounds in wine, including sugar. Only the unbound sulphur dioxide is able to fend off oxygen and microbes. So, sweet wines need plenty to protect them.
The importance of quality grapes Rotten grapes make rotten wine, and need more sulphur dioxide to keep the bugs under control. Grapes with plenty of acidity also need fewer additions.
What are the adverse effects?
Sensory – an excess of sulphur dioxide produces a smell of burnt matches, but an awful lot needs to be added to have this effect. This fault is rare.
Health – is a difficult issue because there is little proof of adverse effects. It may induce asthmatic attacks in some people. It is worth noting that normal food metabolism in the body generates much more sulphites than you would absorb from wine consumption.
In my opinion, the addition of sulphites at the right time and in the right quantity is beneficial, if not essential, for almost all wine.