By Fabio Mencarelli
Maceration, maceration, maceration today in wine making world, is one of the most used terms. Why? because the extraction of enochemical compounds from grape is not economically sustainable. The most extraction we can obtain i.e., with horizontal fermentation tank, very invasive (formation of a lot of lees), energy consuming, is 70 % depending on variety and maturity stage, but then a recovery of wine from lees is needed thus a vacuum rotative filter is used which requires further electricity.
The equilibrium between extraction quality and electricity consume is very hard to find because:
- We do not know the cell maturity in the vineyard (Glory method is a lab analysis time and work consuming, thus money) thus we estimate
- We do not know what and how, selectively, to extract depending on the wine project
- The biochemical knowledge in winemaking is scarce especially in relation to several environment parameters
- We use to make a blend, to have an average, in grape maturity at harvest (unless the vineyard is small e perfectly homogenous), in vinification, in wine fining.
I give below some examples of wrong or unknown operations:
- Use of enzymes in maceration pre-fermentation: most of time the pectolytic enzymes are used at low temperature (4-6°C), only 10-20% of them is working because the optimal temperature for their activity is between 20 and 25°. If you find a good result is not due to enzyme but to temperature and, if you have done a comparison between maceration with and without enzymes, you must be sure of the amount of enzyme concentration, the size of vat and temperature inside the vat are the same in both vats which is almost impossible. Thus, warning in throwing away money
- Use of mechanical extractor: whatever is the system to remove the cap in the liquid, the extraction depends on the temperature; initially, enzymes (grape and yeast) are working and they require specific temperatures, as we said above, thus the stratification of temperature is partially solved with mechanical movement and, especial, with high vertical fermentation tank with a thick cap, the electricity req is very high. Energy consuming is also high for pumping over and delestage which guarantee high mixing rate but only for a moment.
- Use of airflow to homogenize the mass: these systems are less invasive and less energy consuming even though pumping over is not needed; moreover, they are automatized thus less labor cost. They are very useful to homogenize temperature in the vat. One system is using big air bubble blowing from the bottom of the vat in the must, creating a boiling-type movement; the problem with the big bubble is that they could get preferential routes depending of the thickness of the cap; if the rate of bubbling is increasing, the more extraction is obtained the more energy is required and the more lees. The other system is the one using desegregating waves created by sequential air jets (very small bubbles) placed in the bottom of the vat, around the vat circumference. This is a physical approach based on resonance frequency which everybody has thus also the cap; thus when the liquid wave, pushed by the air jets, reaches the frequency of the cap resonance, cap is disaggregated. Practically speaking, the cap is not formed. This is very useful with high vertical vat with thick cap, but it works also with small vat. The energy consume is reduced and the labor cost. Important the accurate management of jet frequency and the jet yield.
- Carbonic maceration: in the wine sector carbonic maceration is well-known but rarely is done accurately, meaning that only grape bunches should be under CO2 not the liquid. The metabolic effect is intriguing but is also energy consuming as we use carbon dioxide as we use dry ice, unless we wait for the CO2 formation by respiration. We have used nitrogen instead of carbon dioxide with surprising results in term of aromatic quality because the response of grape metabolism is different. In this case by using a nitrogen generator it is easy to saturate the ambient or, if nitrogen is used only at the beginning, successively, we have an atmosphere rich in nitrogen and CO2
In conclusion, not always what is known from long time is correct and science is important.
Full Professor of Innovative Technologies for Food and Enology at the University of Pisa, Italy, has been working since the 1979 on postharvest technology and physiology of fruits and vegetables (controlled atmosphere, shipping). In 1993 he started to teach Enology and to run researches on postharvest treatment of wine grape to improve the wine quality. Since 2000, he has been working on wine grape dehydration and on the application of non-destructive techniques on grape and wine with NIR-AOTF, electronic nose, fluorescence sensor and magnetic resonance imaging. In more recent years he has been working on ozone treatment for sonification and product disinfection and also on wine grape to produce a wine without sulfites addition (International Patent PUROVINO). He has been publishing more than 200 scientific papers and he is the Editor of the book Sweet, Reinforced and Fortified Wine printed by Wiley and Sons. Actually, he is also Executive Editor of Journal of the Science of Food and Agriculture by Wiley and Sons.