How to keep your wine fermentation under control

Wine is not a drink.
It’s a lifestyle.
It’s a feeling.
It’s a work of art.

And one of the most important questions is: how to keep fermentation under control?
One answer is density measurement.

Density measurement – the safety inspector of wine production

In the world of density measurement grape juice is considered to be a sugar-water solution, which means that winemakers can measure the sugar concentration in their juice with the help of a density meter. All other components – besides sugar and water – that are present in the juice have so little effect on the density that they do not influence the measured result in any way. The sugar concentration in the grape juice is the main factor influencing the alcohol content of the final wine. By measuring this sugar concentration winemakers can already predict the alcohol content of their future wine before the fermentation has even started. Furthermore, in many countries the sugar concentration is decisive when classifying the product as quality wine or ordinary table wine.

During fermentation the sugar turns into alcohol and CO2, so fermenting wine is considered a three-component solution made of water, sugar, and alcohol. From a theoretical point of view this would be the end of the story in which density plays the hero’s role, but in reality that’s not the case! Winemakers follow the decrease of density during fermentation in order to judge whether the fermentation proceeds as planned. Due to the influence of alcohol this value is called ‘Apparent Sugar Concentration’.

Carrying out proper fermentation control is one of the most important quality control tools a winemaker has as only a finely tuned alcoholic fermentation will reveal all the grapes’ hidden aromas. Winemakers can immediately step in if they see that the fermentation is proceeding too quickly – which could lead to lost aromas – or is about to stop unexpectedly. By adjusting the temperature of the fermentation tank it is in most cases possible to lead the fermenting wine back on track. In more challenging cases a ventilating tank-to-tank transfer might help. A fermentation which is completely stuck can only be reactivated by inoculation with fresh yeast. However, this yeast has to deal with difficult conditions as the nutrients have already been consumed by the first yeast. Furthermore, the ratio of glucose to fructose is not ideal as the glucose necessary for activation of the fermentation might already be exhausted, too. Having these facts in mind, we clearly see that prevention is better than cure. To summarize: dealing with the natural process of fermentation does not mean we cannot use tools to help us keep control.

Bubbles everywhere during fermentation!

Fermentation control is one of the decisive factors for obtaining the wine you intended to produce. However, all methods of density measurement – be it conventional methods like glass hydrometers or digital density meters – are strongly influenced by the CO2 present in the fermenting sample. Of course samples can be degassed to reach a correct result, e.g. by putting them into an ultrasonic bath, via shaking the samples and snifting to release the CO2 or by stirring – although this will not be very convenient if a winemaker has 100 tanks to be measured once a day. Here are two quick options for a successful measurement on fermenting wine with digital density meters.

Turned 90°

The portable density meter is simply turned 90 ° counterclockwise so that all bubbles move in the same direction – to the position in the glass measuring cell where bubbles have the lowest influence on the result. Furthermore, by holding the instrument in this position during your everyday measurement, the results are comparable from one day to the other. And the ultimate benefit is: The winemaker can stay in an upright position :o) unless measuring tasks are seen as a fitness workout!

Syringe filling

Another possibility is to use the syringe filling option: the instrument is prepared for syringe filling (the adapter is usually included in the delivery) and the sample is degassed directly via syringe with the help of creating underpressure. Simply fill the syringe with sample, close the syringe tip with your finger and pull the plunger and remove your finger from the tip. Enjoy the “plop!” sound telling you that the CO2 is leaving your sample. Repeat this routine 3 times. Again you are ready to take a repeatable measurement.

Automation is the helping hand

RFID – that’s not a robot from Star Wars but a technology helping winemakers to quickly identify their tanks before they do a density measurement for the purpose of fermentation control. RFID stands for Radio Frequency Identification and is also commonly used for e.g. container tracking in logistics, goods tracking in supermarkets, and for personnel cards. An RFID tag programmed with a unique sample name is attached to the wine tank or barrel. The density meter reads this tag before the measurement and identifies the name of a sample in a second. Especially when handling a large number of tanks or barrels each day this kind of quick sample identification adds up to an enormous time saving. As the sample ID is saved with the measured values, results are traceable no matter how many different instruments and operators are involved in the measuring process. Not bad, especially if you have to measure hundreds of samples a day.

Here is what Stéphane Thibodaux from Domaines des Comtes Lafon winery in Côte-d’Or region, France, has to say:

“I need to check the densities on around 200 tanks a day. As I now have RFID tags installed for sample identification on each of these tanks, the daily check is done in around 2 hours with the DMA 35*. With my old hydrometer this would take me almost the whole day!”

* DMA 35 is a Portable Density Meter from Anton Paar

Preserving color and taste

Frequently, sulfurization is applied to wine to preserve the color and taste, enhance stability, and avoid any bacterial spoilage. Sulfurization is usually done in the form of a stabilization solution that has to be adapted based on the volume. To see whether the stabilization solution has the correct concentration, again a density meter can be used. Based on the density result you can determine the concentration of two-component solutions like liquid sulfur dioxide.

A wine’s passport

Many analytical labs specialized in wine analysis offer a comprehensive analysis of the wine including alcohol, extract, SO2, acids, pH, and more – an analysis that bigger wineries will even do themselves. For a smaller winery, doing such an analysis means sending a certain amount of sample to the lab that will charge for the respective analysis package ordered. Sophisticated instrumentation based on FTIR or NIR technology are used for the measurements and these instruments are usually capable of measuring several parameters in one go (see e.g. the Alcolyzer Wine Analysis System from Anton Paar. In several countries these official labs will be the ones providing their results for the purpose of issuing a national test number, showing the consumer that the wine has undergone official tests.

Learn more about the DMA 35 Portable Density Meter, an instrument that will do hundreds of fermentation checks a day for you and supports all well-known winemakers worldwide in their production process.

Would you like a quotation for a portable density meter tailored to your needs?

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