Can we determine how the chemical composition of a wine affects its quality? A study by the University of Minho gathered chemical data on red wine samples of Portuguese Vinho Verde wine. Let’s see if these measurements can tell us what to expect about a wine’s quality.
We know intuitively that many factors could influence a wine’s perceived quality. Plenty of rules of thumb exist around wine that you may already be familiar with. Weather effects on the grape harvest, if a cork snaps easily, observing the “legs” as you swirl the wine around, and of course storage environments are all features we may associate with a wine’s quality. This data goes beyond those intuitive features and provides information that you may not think of, that is unless you are a chemist or sommelier.
Chemical tests provide us with a different perspective of the wine as a substance. Acidity, sugar, sulfur dioxide, and most notably, alcohol content, was all measured for this data-set. Alongside these objective measurements was a subjective quality rating given by wine experts. Let us find out if there is more to a wine’s quality than the rules of thumb may provide. We will use this data to answer a few important business questions that could benefit wineries, restaurants, or anyone who just enjoys a nice glass of wine.
Which single chemical component should be focused on to control resulting quality?
Imagine you own a winery (dream come true for many of us I’m sure!). If you could make excellent wine by changing just one thing, which would you choose? Luckily, we can perform an analysis to help us answer that question.
Ideally, we would like to find a way to predict the resulting quality rating on a set scale given the chemical make-up of a wine. A particular method called an ordinal regression can do just that. The ordinal regression is named so because it’s designed to predict an ordered output such as a grade, or in this case, a quality rating.
Inputting the chemical information into an ordinal regression informs us not only which components tend to predict quality, but also to what extent. The extent of a component’s effect is expressed numerically and referred to as the coefficient. The coefficient determines how much the output (the quality rating) changes as the component changes, holding all other factors equal.
The ordinal regression output showed the volatile acidity measurement as the most impactful with a coefficient of -3.079. This means that as volatile acidity increases, the predicted quality rating decreases by about 3 times that amount!
We can visualize this relationship by plotting the volatile acidity for each quality rating:
Clearly the higher quality wines boast a much lower average volatile acidity, almost half that of the lower quality wines. What exactly is the volatile acidity though? According to Decanter.com, the volatile acidity refers to acidic gas and aromas which can sometimes give off a smell of nail polish remover in high enough concentrations. Not something you’d look forward to when enjoying a glass…
Volatile acidity is typically more present in wines made in older barrels, made from dried grapes, or just from being more exposed to oxygen. For wine makers, controlling the wine making process to reduce volatile acidity can have the most impact on a wine’s quality rating.
So what makes a good wine then?
We now know reducing volatile acidity works to achieve a higher quality wine. But what about the other end of the spectrum? Did the analysis result in any features having a positive coefficient, or in other words, predicted a higher quality rating as they increased?
Sulfate content had the highest positive coefficient in the analysis at +1.947. This means that as sulfate content increases, the predicted quality rating increased by almost 2x that amount. Let’s take a look at another chart to help visualize the relationship.
Contrary to what we saw with volatile acidity, the sulfate content is higher among the better quality wines. The change is not as pronounced though, only increasing by about 30% end to end.
What are sulfates exactly? Healthline.com provides some great information on sulfates and wine. Sulfates are sulfur-based compounds that help with food preservation, especially to prevent oxidation in wine. They also help to preserve appearance and shelf life. Sounds like a great way to counteract any negative effects from volatile acidity. Be careful though! Interestingly, higher sulfate concentrations have been linked to worse wine headaches. That could also just be the alcohol though.
How can a restaurant, winery, or other business use this information for their benefit?
Understanding the chemical components of wine and how they affect the quality is important knowledge for wineries and restaurants. But how exactly can they put this knowledge to good use? Sales, of course. And the best way to make sales is recommending a good wine that customers will be sure to enjoy both in quality and price.
Recommending a wine is itself an art form. Everyone has different tastes and experiences. Some may be ordering their very first glass, while others may know their way around grapes and want to try something new. Armed with a chemical profile, businesses can use this method to predict the quality, allowing them to purchase, price, and recommend good wines before anyone at the restaurant has even tried it. For winemakers, advanced knowledge of a wine’s chemical components can help them control the process and mitigate any negative effects.
The results of this analysis give us a better understanding of how a wine’s chemical composition affects its quality. Of course, there is so much more that determines whether someone will enjoy a wine. Something as simple as time of day could influence our palate. No matter what any data says though, only you can decide for yourself what a good quality wine is to you. Cheers!
If you’d like to learn more about this analysis check out my Github repository for this project.
