A Nightmare on Filtration Street

With whispers of Halloween in the air, I thought it might be a smart idea to give this blog post about a specific problematic glucose polymer in wine a more haunting theme. You might not believe in ghosts (neither do I), but glucans in wine are very real and many winemakers all over the world have been haunted by them come filtration and bottling time.

Glucans: cause and effect

Glucans are commonly found in plants and microbes, so it follows that they will also be present in grapevines as well as yeast and bacteria. Luckily not every wine is afflicted by glucan issues, but when it comes around, you’ll be sure to find out about it eventually.

Various defects are attributed to high glucan levels, which include the following:

👻 Filtration issues (otherwise put, clogged filters).

👻 Haze formation and colloidal instability.

👻 Increased microbial instability.

A (not so) fun guy called Botrytis

Broadly speaking, most wines that test positive for glucans were at some stage in their lifetime microbially compromised – going as far back as the grape stage. Ostensibly, the most common cause of elevated glucan levels in wine is a fungus called Botrytis cinerea. This fungus infects grapes and produces glucanases and cellulases which break down structural polysaccharides in grape cell walls, thereby releasing beta-glucans.

Adding insult to injury, the Botrytis fungus also produces large amounts of β-glucans as part of its cell wall structure. During infection, the fungus secretes these β-glucans into the grape berry, adding to the winemaker’s filtration woes. And the final nail in the coffin (getting tired of the Halloween references yet?) is that these glucans persist during most winemaking actions and finally come back to haunt the winemaker during filtration. That’s OK when you’re expecting it, as glucans come with the territory when it comes to the production of delicious dessert wines (click here to read about Noble Rot). And click on this if you would like to see a protocol on the fermentation management of rot infected grapes.

That wild fermentation can take your wine on a wild ride

Now that we’ve established that pathogenic fungi can lurk in the vineyards, the astute winemaker should also don his Ghostbusters cap in the cellar. This is because various microbial ghouls that might be present in your cellar can generate glucans and eventually also quite a scare during filtration and bottling. Note that extended lees contact (from both yeast and bacteria) can also contribute to elevated glucan levels, but I’m not going to focus on this for now.

Industrial yeast and bacteria starter cultures are specifically selected not to contribute to glucan issues in wine. But what about other unwelcome microbial presences? Wild LAB and yeasts, which are typically unidentified and allowed free reign in ‘spontaneous’ or wild fermentations, can produce undesirable levels of glucans and other byproducts. Some seedy bacterial characters include Lactobacillus brevis, Pediococcus damnosus, and certain wild Oenococcus oeni strains. Note that stuck or sluggish fermentations can also contribute to glucan issues, seeing that they lead to extended fermentation times, which provide more opportunities for undesirable microbes to proliferate and produce glucans. Yeast genera such as Candida, Pichia, Hanseniaspora, Saccharomyces (wild strains), and Saccharomycodes come to mind and can all join the impromptu Halloween party in your vessel.

This underscores the value of using controlled starter cultures in winemaking and good cellar hygiene. And when all else fails, there is always ß-glucanase, an enzyme that hydrolyses (breaks down) beta-glucans, thereby drastically improving filtration. Contact me (be***********@*****rt.com) if you want to know more about this enzyme.

The eternal battle between spoilage microbes and the winemaker continues, but at least now you are armed with the freshly acquired knowledge from this blog post, enabling you to better manage unwanted microbes and their byproducts. And lastly…

Boo!