Is protein stability wine’s holy grial?

During a recent fining trial of a problematic wine that was fermented with a problematic yeast, the conversation briefly touched on protein stability and I started reminiscing about the very first blog that I wrote for Laffort South Africa. Said blog post (click here to read it) was about bentonite and its affinity for various proteins or the lack thereof.

Bentonite – Jack of all trades, master of some

Whether you love it or hate it, this bentonite stuff really is a very versatile oenological additive. For those that are a bit hazy (see what I did there) on the subject, here is a quick recap on what bentonite is and what it does.

Bentonite, which is essentially a very useful negatively charged clay, is mainly composed of plates of silicon and aluminium oxide, along with calcium and sodium ions. Upon rehydration, the above-mentioned plates separate, thereby creating a huge surface area that allows the sodium and calcium ions to interact with positively charged heat unstable proteins. The resulting floccules then settle out over time, thus removing the protein. It should be noted that there is some debate on which is better – the sodium or calcium variation. It really comes down to winemaker preference, but it should be added that calcium bentonite could contribute to calcium instability in wine.

In addition to also speeding up clarification in general, it has also been shown that bentonite can remove phenolic compounds. Unfortunately, desirable aromatic compounds can also be removed by this mud we call bentonite. Then, there is also the ‘little’ matter of product loss due to the high lees percentage and contribution towards a cellar’s solid waste, as well as the issues of renewability and biodegradability. So, there are positives and negatives. But the water is starting to get really muddy now and I’d rather move on to some other fining agents relating to protein stability.

And second place goes to…

For now, let’s forget about the pie in the sky alternatives to bentonite and look at what is readily available. Unlike bentonite, carrageenan is renewable as it is a polysaccharide extracted from red seaweeds. While it was generally found that compared to bentonite, slightly less carrageenan can be used to make a wine protein stable, it’s far from perfect. Depending on the type of carrageenan, timing of addition is vital (it does not play nicely with wine), sodium and calcium levels need to be monitored, and there is the cost impact as well. Click here to read more about carrageenan use in oenology.

Pie in the sky

To round of this blog post, we should look take a look at one forthcoming attraction relating to protein stability. Winemakers are well acquainted with CMC (carboxymethylcellulose) and its role in cold stability by now. So, it might not be too far a stretch to suggest that DCMC (dicarboxymethylcellulose), another member of the cellulose family, could also eventually reach the critical acclaim that CMC did on the oenological stage by adequately addressing protein stability.

Very shortly, the abstract of a study I found (click here to read it) suggested that DCMC, applied at dosages similar to that of typical bentonite additions, shows promise. Compared to bentonite, protein stability was generally achieved and lower changes in wine pH and phenolics were observed, with a reduction in calcium content. Regarding aromatic components, the impact of DCMC was similar to that of bentonite treated wines. Another feather in the cap for cellulose (the base compound of both CMC and DCMC) is that, unlike bentonite, it is renewable and biodegradable. Greenies rejoice!  

A former colleague once told me that protein stability is the oenological holy grail. While I won’t go that far, protein stability is a critical control point in winemaking and certainly deserves its fair share of attention.

That being said, bentonite gets the job done and it ain’t going nowhere. At least for now.