steam distillation; alcohol content; wine

Chapter 14

The detectives turn up the steam on alcohol determination in wine

📁 Case overview: After a very cheesy adventure, the detectives are ready to add wine to their portfolio. For the group of five, the only thing better than drinking wine might just be analyzing wine. So when a case on alcohol determination in wine lands on their desk, the detectives are ready to gulp it down. But can Eggcule Poirot convince Miss Mapple that his steam distillation method can produce the same valid results as classical distillation set-ups? Read on to find out.

Eggcule Poirot has the detectives over for dinner. Nancy Beef is also in attendance, but only after making sure there would be no steaks on the menu. For starters, Poirot serves them cheese, grapes and wine. At first, they chatter happily about their last cheese blending case. As has become rather typical, the friendly conversation turns to friendly bickering as the detectives munch on their appetizers.

The argument begins once Eggcule Poirot makes the explosive claim that French wine is the best. Offended, Nancy Beef insists Swiss wine is extremely underrated. Miss Mapple interrupts to state that actually there is no wine like the UK wine. Not to be left out, Lieutenant Cornlumbo joins in defending a good California red. Shallot Holmes watches and sips his wine in amusement. He clears his throat and whistles to get their attention. He is happy to let them know, that in a funny turn of events, they would be indeed performing alcohol determination in wine for a client the next morning.

The detectives are ecstatic about the news and manage to finish the rest of their dinner peacefully. The next morning, everyone has a bit more jump in their step as they enter the office. They are excited to get on this case.

Shallot Holmes is happy to see his team so worked up. He offers Eggcule Poirot, as an excellent host and everything-connoisseur, the lead in the case. Poirot happily obliges and reads over the case file.

He then proceeds to give his team a bit of background information. The client is interested in methods of alcohol determination in wine for labelling and taxation purposes. The client is from Germany, so Poirot is relieved there would be no continuation of the wine battle from the previous night.

Instead, the detective proposes to develop a steam distillation method for alcohol determination in five different wine samples with varied alcohol concentrations. He would then compare the method to a classical distillation setup as a reference method (EEC 2676/1990 (wine) and OIV-MA-AS312-01A (wine) to ensure the customer of the validity of the technique. The rest of his team support his plan of action.

To start developing the alcohol determination process, the detectives choose the following samples:

Sample NameDeclared alcohol content (v/v%)Product details
Wine 111.5Sprakling wine (dry)
Wine 213Red wine (sweet)
Wine 311.5White wine (dry)
Wine 49.5White wine (sweet)
Wine 513.5Red wine (dry)

Eggcule Poirot then takes the team through the steps of the steam distillation process they need to follow for alcohol determination in wine:

1. Connect chiller and preheat distillation unit by running a preheating step twice.
2. Fill the 25 mL volumetric flask and a flask containing deionized water in the water bath, maintained at 20°C for 15 minutes.
3. After conditioning, remove the excess liquid with a Pasteur pipette, adjusting the volume to the 25 mL calibration mark.
4. Immediately, quantitatively transfer the sample into a 300 mL sample tube. Rinse the volumetric flask three times with about 25-30 mL of distillated water to ensure that all the ethanol is transferred into the sample tube.
5. Mount the sample tube on to the distillation unit.
6. Fill a 200 mL volumetric flask with approximately 1 mL of distilled water and place it at an angle under the shortened outlet connection. Poirot emphasizes that the outlet nozzle must end above the calibration mark and touch the glass wall of the volumetric flask. Poirot mentions that for a non-shortened outlet tube, the outlet tube needs to be rinsed after the distillation to avid any possible loss in alcohol content. Here, Poirot highlights that the team must consider the volume needed for rinsing the tube. They should be prepared to stop the distillation early enough to avoid overfilling above the calibration mark.
7. Set-up the distillation according to the following parameters:

Method Parameters EasyDist
Steam stepsNo
Steam power (%)100
Level detectionoff
Distillation time600s
Instrument settings
MaxAccuracy ModeOn
Chiller/Tap WaterChiller F-314
Set Temperature10 degrees

Distill until the volume is just below the calibration mark on the volumetric flask.

8. Quickly detach the volumetric flask, stopper it and place it in the thermostatic bath at 20°C for 15 minutes.
9. Make the volume up to the calibration mark with 20°C conditioned deionized water, stopper it and mix well.
10. Fill a 10 mL syringe with the distillate. Flush to get rid of the air bubbles if any.
Attach the syringe to a density meter and inject the liquid in the density meter cell. Eggcule Poirot pauses to explain that the digital density meter converts the results automatically from density to alcohol content. The volumetric percentage (% v/v) is correlated to the density of the distillate according to International Alcoholmetric Tables (OIML)
11. Finally, calculate the alcohol content by applying a factor of 8.

After he finishes, Poirot asks if there are any questions.

Miss Mapple asks how he plans to compare his process to the classical set-up for alcohol determination in wine.

Eggcule Poirot is happy she brings this up. He explains that to compare the system specifications according to EEC 2676/1990 and OIV-MA-AS312-01A, they need to inject the tempered ethanol/water mixtures directly into a density meter. To compare their results obtained by steam distillation to distillations performed with a classical set-up, they also need a classical set-up.

Poirot proposes to set up an alcohol distillation stand according to Commission Regulation (Ec) No. 2870/2000 Appendix ll Method B. In the classical method, a 50 mL wine sample is carefully tempered and transferred quantitatively in a round-bottom flask. It is further distilled to 50 mL, followed by density measurements with a density meter.

The detectives set out to carry out the process for alcohol determination in wine, trying hard to resist the temptation of drinking their samples. They end up performing alcohol determination in wine using 25 mL sample sizes in 300 mL sample tube for distillation and 200 mL volumetric flask for receival of the distillate.
After they are finished, they gather to examine their data.

Product and declared alcohol contentReference value Ethanol in % Vol classical distillation*Measured after steam distillation in % volFactorMeasured after steam distillation with dilution factor (*8) in % vol
Sparkling wine (dry)
11.5% vol
Delta % v/v#-0.001
Red wine (sweet)
13% vol
Delta % v/v#-0.006
White wine (Dry)
11.5 %vol
Delta % v/v#-0.022
White wine (sweet)
9.5 %vol
Delta % v/v#-0.012
Red wine (Dry)
13.5 %vol
Delta % v/v#-0.012

# difference in alcohol content between the reference method with classical distillation and after steam distillation

Miss Mapple is still a bit skeptical that they could convince the customer to use their steam distillation process over a classical set-up for classical determination of alcohol in wine.

Eggcule Poirot appreciates her stubbornness. He pulls out literature that shows that according to regulation EEC 2676/1990 and OIV-MA-AS312-01A any type of distillation or steam-distillation apparatus may be used, if it fulfills the following conditions:

  • Ethanol-water mixtures with an alcoholic strength of 10.0% volume are distilled five times in succession. The distillate should have an alcoholic strength of at least 9.9% volume after the fifth distillation. In other words, the loss of alcohol during each distillation should not be more than 0.02 v/v%.
  • EEC 2676/1990 (wine) Loss of alcohol must be ≤0.1% when distilling a 10% ethanol-water mixture five times in succession
  • EEC 2676/1990 (wine) Loss of alcohol must be ≤0.1% when distilling a 10% ethanol-water mixture five times in succession
  • OIV-MA-AS312-01A (wine) Loss of alcohol must be ≤0.1% when distilling a 10% ethanol-water mixture five times in succession

Eggcule Poirot concludes that their steam distillation setup on a single 1:8 distillation of about 10 v/v% ethanol/water mixture closely fulfills the system specification requirement according to EEC 2676/1990 & OIV-MA-AS312-01A, with an amended distillation method to achieve the required recoveries. Their 1:8 steam distillation of several wine samples with a steam distillation system resulted in Delta % v/v i.e. loss of alcohol compared to classical distillation (with Karl Steinicke apparatus) ≤0.1% v/v.

Miss Mapple is reassured and Shallot Holmes also expresses confidence that their process will perfectly satisfy the client’s requirements for alcohol determination in wine. He suggests optimizing their protocol using the 18 cue cards with steam distillation tips. Once they do and present the client the data and their findings, he is extremely happy with their work and gifts them several bottles of his finest wine.

The detectives had a fine celebration with their German wine and agreed that they must simply taste the best from all regions of the world, as good wine can come from nearly anywhere.