By Jim Harbertson, Associate Professor of Enology, WSU-IAREC
Recent work published in the Australian Journal of Grape and Wine Research evaluated the effect different fining agents have on wine tainted with smoke (Fudge et al. 2012). The experiment used Vitis vinifera ‘Pinot noir’, ‘Cabernet Sauvignon’ and ‘Merlot’ wines which contained volatile phenolics that are responsible for the smoke aromas and flavors [guaiacol, 4-methylguaiacol, syringol and tricresol (mixture of o-, m-, and p-cresol)]. This trial evaluated 13 different fining agents in an initial bench trial using Pinot noir wine. The fining agents selected are commonly used in the wine industry with one exception (Table 1).
|Table 1 – Fining agents tested in Fudge et al. 2012.|
|Protein||egg albumin, casein (potassium salt), isinglass, gelatin|
|Bentonite||sodium bentonite (Plusgran gel, Volclay), calcium Bentonite (Microcol-Cl)|
|Yeast Hulls||Biolees, Biocell|
|Synthetic||polyvinylpolypyrrolidone (PVPP), synthetic mineral|
|Activate carbon||with and without silica gel|
Polyvinylpolypyrrolidone (PVPP) is basically a form of nylon, which is typically used to remove small molecular weight phenolics from wines in an attempt to remove bitterness. Currently, I have little information regarding the use of synthetic mineral, but am actively searching. The first trial showed that only the activated carbon (sans silica gel) and the synthetic mineral significantly reduced the concentrations of the various volatile phenols associated with smoke taint. Activated carbon removed 58-70% of the all of the volatile phenols, whereas the synthetic mineral was more variable, slightly less effective and removed 8-58% of the volatile phenols. The synthetic mineral was not very effective at removing guaiacol or tricresol. In this experiment, none of the fining agents removed the bound forms of the volatile phenols. Of practical importance, this means that if the amount of the bound compounds is large enough, the smoke taint aroma could return.
Following the bench trial, additional work was done on smoke-tainted Cabernet Sauvignon and Merlot wines. The wines were not as tainted as the Pinot noir, but similar enough for comparison. For this experiment only the fining agents that were effective in the bench trial were used, with the exception of the activated carbon and synthetic mineral, which were used by themselves and in combination (same concentration as the initial experiment). The effectiveness of the fining agents was not affected by wine type. The activated carbon removed 61-71% of the volatile phenolics whereas the synthetic mineral removed 0-55% of the volatile phenolics (still ineffective at removing guaiacol or tricresol). The combined fining treatment was either the same as the activated carbon or significantly more effective at removing all of the volatile phenols.
Descriptive sensory analysis was also conducted on the wines. The activated carbon and the combination of the two fining agents were able to significantly reduce smoky aromas and “ashy aftertaste,” while the synthetic mineral reduced the smoky aromas to a lesser extent but had no effect on the “ashy aftertaste.” The authors concluded that the activated carbon was the more effective of the two fining agents, and that the effect of the combined fining agents was driven by the activated carbon. The authors also noted that both fruit aroma and fruit flavor significantly increased with the wines treated with activated carbon but not the synthetic mineral. Color was also unaffected.
In conclusion, this work shows that smoke taint cannot be removed with the majority of commonly used fining agents. However, many of the fining agents used in this experiment are not typically used to remove aroma compounds. For example, protein-fining agents are typically used to remove tannins, which are decidedly non-volatile The same is true with bentonite, which is used to remove proteins. The fining agents that are more typically used for aroma issues such as activated carbon were effective, although the addition of silica gel to an activated carbon reduced its effectiveness almost completely. The synthetic mineral was somewhat effective, although it is not clear what exactly synthetic mineral is and whether or not it is legal to add to wine in the United States. The questions about synthetic mineral may not be worth pursuing, as the activated carbon was far more effective at reducing smoky aromas, flavors and aftertastes. The lingering issue with the treatment of wines with smoke taint is that the treatments that have been successful are only capable of removing the volatile forms. The bound smoke taint compounds are elusive and the potential risk of smoke taint returning in the wine remains.
Fudge, A.L., M. Schiettecatte, R. Ristic, Y. Hayasaka, and K.L. Wilkinson. 2012. Amelioration of smoke taint in wine by treatment with commercial fining agents. Australian Journal of Grape and Wine Research. 18:302-307.
See also: A Note on Smoke Taint