Besides bread based confections, making alcohol from fruit is one of the oldest biotech processes. But what is really behind the transformation of grapes into wonderful wines, or even champagne?
As we are talking about biotechnology, it is crucial to discuss the micro-organisms involved in the process. But I think you would also love to know how you get different colours in wine!
Contrary to popular belief, the difference in wine colour does not depend on the kind of grape used, but lies in the order of steps in the wine-making process:
- Grapes, which are put into fermentation directly and pressed after, will produce Red Wine
- Those who are first pressed and then put into fermentation will make White Wine
This means you can make white wine from grapes too.
In other words, the fermentation of the juice only or the fermentation of the whole grapes change the color of the wine. For the taste, it will also depend of the barrel (wood, steal or terracotta jars)…and secret ingredients added by the vineyard, both during the Aging period (Élevage in French).
What about “rosé“?
The production of that pale pink in-between type of wine, rosé, uses the same process as for white wine – except a different type of grape is used in this case.
Otherwise, after vinification, some vineyards like to simply mix a little red and white wine together, which is kind of cheating, but as long as the result remains tasty, it seems fine to me 😉
And the microbes?
Now, the micro-organisms used for the fermentation. In fact there are two different types:
The first used is a yeast that transforms the sugar in alcohol + CO2. Typically, the yeast culture needs around 15-20g of sugar to create 1%vol of alcohol. And of course. the most commonly used yeast is Baker’s Yeast – aka Saccharomyces cerevisiae. The type of yeast used also impacts the final result.
Secondly, a bacterial culture reduces the acidity of the wine. This is for malo-lactic fermentation, (transforming malolactic acid into lactic acid + CO2). Examples of such species of lactic acid bacteria include Oenococcus oeni and the process takes place during the second fermentation stage.
So, there are essentially two fermentation stages with two types of micro-organisms.
How to stop the fermentation process
To ensure the stability of those bacteria and yeasts, Sulfur dioxide (SO2) is added to the grape juice at the beginning of the process (to protect the wine from bad cultures growing and preserve its integrity / stop ‘browning’). The fermentation process can also stopped by cooling down the temperature (i.e. preventing the microbial enzymes involved from working efficiently).
Another method used is the adding of a high degree alcohol such as brandy (which kills the microbes), but this also changes the wine — i.e. fortified wine is produced instead.
Also, if you stop the process after all the sugar is consumed, the wine will be “dry“, whereas if it has been stopped before, it will be considered “sweet“.
What a wonderfully logical process, don’t you think?
And why does champagne ‘pop’ when opened?
This popping noise is a result of the third fermentation stage taking place in the bottle.
After the whole wine process is performed and the wine is bottled, a precise quantity of yeast and sugar is added. Due to normal respiration, this culture therefore produces a precise quantity of CO2 that gives you a nice headache if over-consumed!
So now that the secrets of wine and champagne have all but been revealed, I wish you a wonderful New Year’s Eve – and please enjoy such beverages from across the world (because, yes, good wines do not only come from France) in moderation.
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