One very important step in the white winemaking process is the removal of proteins that cause a hazy appearance of the wine while in storage. Often, bentonite is used to remove these proteins, as the negatively charge bentonite will attract the positively charged proteins and settle out to the bottom of the tanks where they can be left behind. Though the use of bentonite is efficient in removing proteins from white wine, some claim it has less than desirable side effects, including the loss of wine since it canâ€™t be reused, as well as the cost of its disposal and potential changes in the aromatic profile of the finished wine. Some studies have shown no effect on aromatics by bentonite, while others have shown it does negatively affect the aroma. As a result, finding an alternative to bentonite for removing proteins from white wines may be important.
Two possible alternatives to bentonite that are the focus of the study presented today are carrageenan and pectin. Carrageenan is a negatively charged polysaccharide that was originally extracted from red seaweed. The large number of sulfate groups on the compound gives it its negative charge and somay function well to remove the positively charged proteins in white wine. Pectin, on the other hand, is a negatively charged heteropolysaccharide compound with many carboxylic acid groups that has been shown to be effective in acidic dairy beverages.
The goal of the study presented today was to determine if carrageenan or pectic could be good alternatives to bentonite in removing proteins from Australian Chardonnay wines and to determine how these possible alternatives affect the chemical and aromatic characteristics of the finished wine.
4 unfined juices from the 2009 vintage using Chardonnay, Sauvignon Blanc, Riesling, and Semillon grapes, as well as 4 unfined finished wines from the 2011 vintage using two Chardonnays and 2 Sauvignon Blancs (all from Adelaide Hills, Australia) were used in the preliminary experiment.
1mL of each wine sample was mixed with 0.5g/L of carrageenan and left in contact for 18 hours before the carrageenan was removed by filtration. All samples were performed in triplicate.
Chardonnay must from the Langhorne Creek region of Australia (2009 vintage) was used for the large-scale experiment. Twenty 20L fermentations were prepared for the experiment. 30mg/L of pectinase was added, cold settled for 24 hours at 0oC, and finally racked.
The following 6 treatments were tested: 1) pectin added pre-racking; 2) carrageenan added pre-racking; 3) pectin AND carrageenan added pre-racking; 4) pectin added post-racking; 5) carrageenan added post-racking; and finally 6) pectin AND carrageenan added post-racking. The concentration of pectin used was 2g/L, and the concentration of carrageenan used was 0.25 g/L. Controls without carrageenan and/or pectin were also produced and tested.
After racking, standard fermentation practices were used on all treatment wines.
After going through a cold stability test, wines were bottled and capped with screw caps 4 months after fermentation ended.
For all wines, protein and polysaccharide content were measured, in addition to undergoing a heat test (measuring the amount of haze produced). The following were also measured and analyzed for all wines: alcohol, specific gravity, pH, titratable acidity, glucose, fructose, volatile acidity, free SO2, total SO2, brix, organic acids, metal content, color, and finally sensory characteristics.
A separate test determined how much bentonite was needed to produce a heat-stable wine (i.e. no haze formation).
For the sensory analysis, wines were evaluated by 30 expert AWRI tasters 10 months after bottling. The panel wrote their own notes about the appearance, aroma, and flavor of each wine, as well as whether or not they noted any faults in the wine.
Panelists were asked to determine which wine was different from the rest in a sample set of 3 wines each. They were given 5 sets representing all of the treatment wines. Panelists were isolated in tasting booths for the sensory analysis. Panelists were allowed a 30 second break in between analyzing each set.
â€˘ Carrageenan significantly reduced the amount of protein in all samples in which the compound was present in the small-scale experiment.
â€˘ The use of carrageenan resulted in a decreased fermentation rate (3-11 days slower than the controls).
â€˘ The use of pectin did not affect the fermentation rate of wines.
â€˘ All fermentations to which carrageenan was added had problems with frothing.
â€˘ At day 12, polysaccharide content was higher in all treatments than in the controls.
â€˘ After bottling, there were no differences between treatments and controls in regards to polysaccharide content.
â€˘ Free SO2, total SO2, specific gravity and residual sugar were not affected by any of the treatments.
â€˘ Ethanol content was about 0.15% v/v lower in carrageenan-treated wines.
â€˘ Volatile acidity was lower in pectin-treated wines.
â€˘ pH was higher and acidity lower in pectin-treated wines.
o Acidity was lower due to lower tartaric acid content (no other acids were affected).
â€˘ Acidity was not affected by carrageenan treatment.
â€˘ All metals were in range of those commonly found in white wines.
â€˘ Fe and Al were decreased in most treatment wines.
â€˘ Mn, Zn, and Mg were significantly decreased in pectin-treated wines.
â€˘ Na was significantly higher in all treatment wines.
â€˘ K was significantly increased in pectin-treated wines.
â€˘ Pectin added pre-racking removed the Al prior to the start of fermentation.
â€˘ Al content was nearly zero for all treatments at bottling.
â€˘ At bottling, pectin added pre-racking had significantly higher levels of Ca than the control.
â€˘ Fe and Zn levels were similar at bottling to what levels were in the must for most treatments.
â€˘ Zn was 30% decreased in pectin added pre-racking compared to all other wines.
â€˘ Mg and Mn levels were significantly decreased in all pectin treatment wines.
â€˘ Na was increased in all treatments at bottling.
â€˘ K levels increased by 20% in pectin-treated wines.
â€˘ B, Cu, S, and P levels were not affected by any treatment.
â€˘ Metal concentrations in wines were more affected by pectin treatment than by carrageenan treatment.
o The authors suggested that if either of these are used as alternatives to bentonite, winemakers may want to consider adding micronutrients to make up for the changes listed above.
â€˘ Color was largely unaffected by the treatments, with no differences detected using the naked eye.
â€˘ In regards to protein removal, adding both pectin and carrageenan after racking was most effective.
o Most of the protein was removed prior to fermentation.
â€˘ By itself, carrageenan was more effective at removing protein than pectin.
o Pectin did not remove as many chitinases or thaumatin-like proteins compared with carrageenan.
â€˘ Pectin added after racking reduced haziness in wine by about 50%.
â€˘ Carrageenan treatments reduced haziness in wines by between 58 and 72%.
â€˘ The bentonite control treatment reduced haziness in wines by between 38 and 76%.
â€˘ Sensory analysis confirmed a significant different between the control wines and the wines treated with carrageenan after racking. No other differences were noted.
o It was not determined if this difference was better or worse, just that it was different.
The results of this experiment showed that the addition of both pectin and carrageenan effectively reduced the levels of haze-causing proteins in white wines, though carrageenan was slightly more effective than pectin. It is possiblethat adding them together might be more effective, though those numbers were not supplied by the authors. It appears as though they are as effective as bentonite in removing protein from wine, so from a simple protein removal standpoint, both pectin and carrageenan would be good alternatives to bentonite.
There were some negative aspects to using pectin and/or carrageenan, including slowed fermentation rates, slightly lowered ethanol content and frothing in carrageenan, and altered metal content in both treatments. Finally, when carrageenan was added after racking, there was a change in the sensory profile of the wine, which may or may not be desirable.
Overall, the results of this study showed that pectin and carrageenan, when used separately or in concert, where just as effective as bentonite in reducing the protein levels in white wine and thus the haziness of white wine. However, I donâ€™t think Iâ€™m ready to say go ahead and make the switch, as there are a lot of questions still left unanswered. The slowed fermentation rate and the frothiness in all fermentation batches when carrageenan was concerning to me, as winemakers would need to come up with effective strategies to avoid or work with these issues.
I was also concerned with the results of the sensory analysis, as it was not clear to me how the aromatic profile of the wine with carrageenan added after racking was affected. It seems like a somewhat poor experimental design to have a sensory analysis that gathers information on differences between wines yet not describe which one actually tastes better. Itâ€™s a simple question that could have received a quick answer, yet it was somehow overlooked. For all we know, that wine could have tasted significantly better than all the other treatments and controls!
Further analysis should examine the sensory changes further, as well as possible mechanisms for combating the slow fermentation rates and frothing issues. It would also be interesting to see if pectin or carrageenan added at different doses would be more or less effective than the doses analyzed in this study, and if adding them together would be better overall than adding them separately. Finally, how effective are these treatments using different white wines? Iâ€™d like to see a range of white wines compared.
What do you think about this study? What would you have done differently? What would you like to see come next in this line of research? Please feel free to leave any comments or questions!
Source: Marangon, M., Lucchetta, M., Duan, D., Stockdale, V.J., Hart, A., Rogers, P.J., and Waters, E.J. 2012. Protein removal from a Chardonnay juice by addition of carrageenan and pectin. Australian Journal of Grape and Wine Research 18: 194-202.