Model Wine: The Use of Ethanol in Enology

By Jillian Jastrzembski

What’s a model wine?

Is that a wine you put on display? Or a wine you try to recreate? Not exactly.

Model wine is a solution made to approximate the chemical behavior of real wine, and is used in research experiments. You can think of it as an over-simplified wine: just the major components. That means water, ethanol, and just a few other organic compounds in much lower concentration.

Why not just use real wine?

Sometimes we do! For example, researchers might use real wine to create an internal calibration curve. An analytical standard is spiked into the sample at several known concentrations, and analyzed. Based on the data, the native concentration of the analyte can be back-calculated.

However, this isn’t always practical. Real wine is incredibly complicated, and contains hundreds of trace-level molecules that may or may not contribute to flavor, aroma, aging characteristics, or other reactions. That makes it impossible to create a chemical replica, and difficult to account for all the changing variables. Besides, real wine is expensive, particularly when an experiment calls for many replicates.

Often, it’s easier to use a simpler model. We want something that can roughly account for the chemical behavior of wine, without muddying the matrix too much.

The major components of wine

Wine is mostly water, with ethanol coming in second at about 12-14%. Everything else is present in relatively low concentrations. Even the flavors and aromas that have the largest sensory impact on wine are present in trace levels, often parts per billion or even parts per trillion.

To make model wine, researchers create a solution of about 12% ethanol in water, and spike in some of the major organic compounds found in wine, like tartaric acid and sugar. The pH of the solution is adjusted to match the pH of a typical wine.

Model wine solutions can differ depending on what’s being tested, and will be specified in the methods section of the research article.

When to use model wine: 3 examples

1. Calibration curves

Wine is too “dirty” of a matrix to be injected into the analytical instrumentation as is, so there is always some kind of extraction method involved. The extraction method will depend on the analyte of interest.

When quantifying compounds in wine, it won’t do to simply use an external calibration curve in water. That’s because the various other components in wine can have a dramatic impact on how much of the analyte gets extracted and makes it to the analytical detector. Ethanol is one of the major culprits because it is present in such large quantities and has a high affinity for many common extraction materials.

One way to solve this problem is to create the calibration curve using a model wine solution. The extraction is performed for each point on the calibration curve in the model wine solution, in order to account for the effects of ethanol and other components.

2. Kinetics experiments

Kinetic experiments represent an important part of enology research. The changes that happen to wine during aging are part of what make it special, AND part of what make it problematic for wine makers. For example, during aging, components of wine react to produce new compounds, resulting in different sensory characteristics. On the other hand, undesirable compounds can be released – and sometimes it’s hard to know where they came from.

One way to study this is to perform kinetics experiments, using a model wine to help uncomplicate things. For example, scientists can spike various phenolic compounds into model wine and see how they react with highly reactive volatile species within a given time frame. This can provide insight into the formation of nonvolatile precursors to odor-active compounds, and ultimately help winemakers have better control over their product.

3. Sensory testing

In sensory testing, model wine makes itself important yet again. The aromatic impact of a given volatile organic compound can change depending on the matrix. Smelling a compound in water alone will not give you an accurate read on its importance in wine. Ethanol in particular can enhance the volatility of odor-active compounds. When performing sensory testing for individual molecules, it’s important to use a model wine solution as the carrier, or at the very least use the appropriate concentration of ethanol.

Conclusion

Because ethanol is the second-most abundant chemical in wine, second only to water, it is an essential tool for enology research experiments. Scientists use model wine solutions as a simplified solution to help them create sensory, kinetic, and analytical models of wine.

The same goes for other alcoholic beverages. Ethanol can also be used to make model whisky, model tequila, and so on. Not only is ethanol ubiquitous in nature, it’s ubiquitous in the laboratory!

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