Chapter 44

Analyte Determination in Wine: Steam distillation vs. the barstool method

📂 Case overview:The detectives assist a friend who is trying her hand at viticulture. Now that the wine has been produced, a number of declarations need to be made regarding the volatile acid and alcohol content. At a loss for how to accurately determine these analytes, she has called on the detectives for help. Can the detectives help get this new venture off the ground and get the product to market? Read on to find out.

The detectives are back in the office, drinking tea and discussing the adventures they had on their recent trip to China . Their client had reported back on the successful implementation of NIR analysis in his corn processing factory and was very happy with the money he was saving and the improvements he was now able to implement. “We should all celebrate a job well done,” says Shallot Holmes. He suggests they all go out for a drink in the evening. “Ooh, that reminds me, I have a potential case for us to solve that involves drinking,” says Eggcule Poirot. Eggcule tells the detectives about his friend who recently bought a vineyard and has produced their first batch of wine. Everything was going well, and the wine had been produced and bottled; however, she subsequently found out about all the declarations that had to be made. At a loss for what to do, she asked Eggcule if he and the detectives could help. “What do you reckon, detectives? I once helped a client in Germany with alcohol determination in wine , and Nancy, you once helped a client determine vicinal diketones in beer . Should we go to France and see if we can assist in getting this business venture off the ground?” asked Eggcule Poirot. “Well, I, for one, am a wine enthusiast,” says Nancy Beef. “The more wine I drink, the more enthusiastic I get!” she says to the amusement of the detectives. Shallot Holmes agrees that the case is worthy of the attention of the detectives and tells the detectives to drink up; they have a case to solve!

The detectives arrive at the vineyard by mid-afternoon, where Eggcules’ good friend Denise Jacques greets them and wastes no time showing them the vineyard. Denise takes the detectives to see the vines that she has labored over. The detectives have many questions for Denise. She tells them all about the importance of selecting the right site, sun exposure, soil preparation, drainage, grape selection, and even about the complex trellis system that supports the vines and provides the ideal structure for grape development. The detectives learn a great deal about viticulture from Denise and are very impressed by her knowledge. She then takes them to the cellar where the wine is stored. Denise gives each of the detectives a glass of her latest batch to sample. It was here that the detectives discovered the gaps in her knowledge. “Once I had produced the wine, I tried to sell it at a local market; I wanted to get some feedback about my wine before trying to sell it wholesale,” says Denise. “I was approached by some officials at the market who made me aware of all the declarations that were required; I was given a warning and had to pack up my things and told not to return until I had made the necessary declarations,” she explained.

Lieutenant Cornlumbo asks Denise how she determines the alcohol content of her wine. “Well, we always use the barstool method for alcohol determination,” says Denise. The detectives were suitably puzzled by this response. “The barstool method? What’s that,” asked Cornlumbo. “Well, you see, when a batch is ready, we sit grandma on that barstool in the corner. We then count how many glasses of wine it takes before she falls off. The current batch is about five glasses strong,” she says. Eggcule almost chokes on the wine he is tasting. “And as for volatile acids, I’m not sure I even understand what they are. I looked up volatile in the dictionary, and it says, ‘liable to change rapidly and unpredictably, especially for the worse’ – we noticed that grandma gets volatile after about four glasses of wine, not long before she falls off the stool,” says Denise. Unlike the other detectives, who look completely perplexed, Shallot Holmes maintains his composure. He explains that in chemistry, volatility describes how easily a substance vaporizes. “Volatile acids are present in wine and are formed by oxidative or anaerobic fermentation. The majority, over 95%, of the volatile acidity in wine is acetic acid, which derives its name from the Latin word for vinegar, ‘acetum’. The word vinegar itself arrived from middle English from the old French ‘vyn egre’, meaning sour wine. High levels of volatile acids are an indicator of low-quality and acetous products. The EU and Switzerland have tolerance levels and legal limits for volatile acids. The USA has its own limits, as do other regions, so you’ll have to ensure the levels in your wine are appropriate for the countries where you want to sell your wine,” Shallot explained to Denise. “Oh, I see, but how do I accurately determine these levels in my wine,” asked Denise. “Well, you did the right thing, Denise; you called the detectives, who will now explain how steam distillation and titration can accurately determine volatile acid and alcohol levels in your wine. Right detectives?” says Holmes to the eager team.

Eggcule, keen to ensure his friends’ wine met the required legislation, explains the steam distillation and titration process that will give Denise all the information she requires. He explains that steam distillation is widely used to separate the components of a mixture, and it is particularly useful for the extraction of volatile or easily vaporized compounds. Steam distillation separates the components in a mixture based on their boiling points. The mixture is heated, and the steam generated vaporizes the volatile components in the mixture. The vaporized components are carried to a condenser, where they are cooled back into liquid form, known as the distillate. The official method for volatile acid determination then requires titration, which is a laboratory technique to determine the unknown concentration of the acid. The process involves the precise addition of a known concentration of solution until a reaction is complete, known as the endpoint. The volume of titrant required to reach the endpoint is proportional to the concentration of the analyte. A calculation is then used for the recovery rate according to an equation. For wine, sulfur dioxide and sorbic acid are also distilled, and these can lead to increased results. To correct for the co-distilled acids, a second iodometric titration is performed, and their value is subtracted from the results. Once having accounted for these co-distilled acids, you will have an accurate depiction of the acetic acid content of your wine.

“Oh, wow, that all sounds very complicated; the barstool method is easy to perform here in the cellar, but steam distillation and titration seem a bit beyond my reach,” says Denise in response. Shallot Holmes tells Denise not to worry, as laboratories could perform these analyses for her. She must send a sample for analysis and wait for the results. The detectives give Denise the details of a nearby testing facility where she should send a sample. Once the results arrive, she can make all the declarations required by law and proceed with getting her wine to market. Denise is very grateful for all the information provided by the detectives, and she gives them another glass of her wine. The detectives raise a glass to a job well done and make their way home. On the journey back, the detectives all chuckle at the barstool method of alcohol determination. A method they would not be recommending to their future clients any time soon.

Case closed