The wine making process is simply the conversion of sugar into alcohol by yeast.There’s no doubt that the wine making process can be a bit complex. There are all kinds of decisions to make regarding varietals, yeast strain, and additives.¬†However, the actual process of how wine is made can be understood in relatively simple terms.

It’s important that you have a working knowledge of this process because everything we as winemakers do is to facilitate this process. We can build on this basic understanding over time, diving into more and more details along the way.

The Simplified Wine Making Process

After a lot of reading and research I’ve been able to boil this process down to a very easy to understand equation. Here is how wine is made:

Grape Juice + Yeast – Oxygen = Alcohol + Carbon Dioxide

We’ll break this down into more detail in time but this is the essence of the wine making process.

The Left Side

On the left side of the equation the first two terms are grape juice and yeast. Combining these, as you know, is what gets fermentation started.

These marvelous little creatures digest the sugar in the grape juice and produce the products on the right side of the equation, alcohol and carbon dioxide. That is, if and only if all of the oxygen is removed from the system.

The yeast consume the oxygen as they build their population so we need some oxygen in there to begin with. However, as long as there is oxygen in the must the yeast will produce water and carbon dioxide. I don’t know about you but from where I’m sitting alcohol sounds much better than watery grape juice.

Thus, in order to produce alcohol the yeast must be cut off from all sources of oxygen. This is part of the reason we store wine in airtight containers during fermentation. Keeping air out not only keeps unwanted micro-organisms out of our wine, it prevents oxygen from entering the system and allowing the yeast to go back to producing water.

Another thing we are tasked with is making sure that only the yeast we choose is able ferment our must. We don’t want just any yeast making our wine, nor do we want spoilage micro-organisms in there making a mess.¬†This is why we add sulfites just prior to inoculating the yeast. We’re setting the stage for the yeast to totally dominate the wine making process as shown above.

The Right Side

On the right side of the equation we have the by-products of fermentation. In reality there are many bi-products of the wine making process. Much more than alcohol and carbon dioxide as shown here. However, alcohol and carbon dioxide are produced in the greatest volume which is why they’ve been singled out here.

As you know the alcohol is the most desirable by-product when making wine. It’s what makes wine wine after all.

The carbon dioxide we can do without which is why we have to go through all the trouble of degassing the wine. Carbon dioxide left in the wine can produce off flavors and be generally unpleasant in wines that should have been still.

The other by-products are not easy to summarize. They are the many flavor and aroma compounds that the yeast produces or shapes from compounds in the grape must. Current research shows there are about 1000 such compounds in wine 400 of which yeast are responsible for. Read here for more.

In Conclusion

Remember this equation.

Grape Juice + Yeast – Oxygen = Alcohol + Carbon Dioxide

This equation is the basis for understanding the entire wine making process. Yes it’s simplified and there is indeed a lot more going on. However, this is enough be able to begin to understand why we do what we do when we make wine. It’s a solid foundation we can build on.

There are some complex processes going on behind the scenes here that aren’t so easily summarized, as I mentioned earlier. Those processes will make more sense if you’ve got this much down.

Photograph by Sagolla