MW Topic of the Week: Stabilization

Hi all

The topic this week is wine stabilization. There are been two direct questions on this recently

Why and how should wine be stabilized before bottling? (2010, and 2019 S1A)
How might protein and tartrate stability in wine be achieved, and managed? (2015)

Does anyone want to tackle the different methods of protein and tartrate stabilizing a wine? 

(I took a look at the examiner's report after my S1A and was surprised to see that the examiners didn't think microbial or color/colloid stability was in the scope of the first question.)

Cheers,

Sabrina

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  • Hi all, I just wanted to add a few thoughts. I'm not an MW student so I may be including technical details that are beyond what the MW is looking for.

    Perhaps this is evident, but I wanted to mention a few high-level concepts on why wines may become unstable in bottle.

    • Changes in temperature during bottle aging can result in instability. For example, decreasing the temperature of wine lowers the solubility of tartrates causing them to precipitate and increased temperature denatures proteins, making them insoluble. Wines should be stable over the range of temperatures that they are likely to experience (everything from refrigerator temperature to warmer room temperature). 
    • Stabilization techniques should be performed on the wine after it has been blended, since stability depends on the wine's overall composition. Stable components can be combined to make an unstable blend.
    • Because the solubility of many of these compounds is interrelated, the order of these stabillization techniques is important (though I doubt you need to know the details around this).

    Cold stabilization

    • Practiced routinely on most white wines sold. My sense is that most small to mid-sized producers are using traditional cold stabilization and larger producers use more fancy techniques like electrodialysis and additives that inhibit crystallization.
    • Many red wines do not require cold stabilization (though I'm sure many producers still do it prophylactically) since the higher phenolic content actually increases the solubility of tartrate salts in red wine. Many small producers do not cold stabilize reds.
    • This practice reduces a wine's TA and can increase or decrease the wine's pH (for initial pH > 3.8 => pH increases; pH < 3.8 => pH decreases) slightly. Probably not necessary to mention, but interesting to be aware of.

    Protein stabilization

    • Changes in temperature, pH, and % alcohol can cause protein instability. At bottling, we're mostly concerned with temperature, however, over long bottle aging, components may become less soluble as the wine concentrates.
    • I was speaking with Megan Glaab, winemaker for Ryme Wines, the other day. She mentioned that she worked in Australia during a vintage with a few VERY hot days in the early 2000's (I believe 2005) and that producers there worried that this would cause protein instability. I haven't looked into it yet, but there may be some interesting examples around this.
    • Again, this is typically an issue for whites, not reds. In general, all of the dry extract (phenolics, tartrates, proteins) in red wine increase solubility of other components. 

    Microbial stability

    • For filtration, it may be worth mentioning "nominal" versus "absolute" filtration methods. Sterile filtration removes yeast and bacteria and uses an "absolute" filtration method with a pore size of 0.4 microns.
    • I'd definitely mention that most wines with residual sugar are filtered.
    • It may be worth mentioning additives other than SO2 used for microbial stability (DMDC or "Velcorin", lysozyme, maybe sorbate).
    • Perhaps worth mentioning pasteurization?

    For each type of instability, there are tests that a winemaker can perform to determine whether it is necessary to treat the wine. For protein stabilization, the test is referred to as "heat stability", for microbial stability, winemakers often run "Scorpions" (PCR-based genetic tests that give cell counts for different common wine yeast and bacteria).

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