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

()

  • I just read the new examiner's report for the stage 1 assessment and the examiners now believe that microbial stability is within the scope of the question. 

  • these questions overwhelm me due to how technical they are and the depth of detail required. Would you go into additives here like CMC or mannoproteins? What about electrodialysis? If so, how would you approach? How do you deal with RS in a question like this? I'd love to know how you'd approach in terms of bringing in specifics, but here's how I think I'd approach an initial intro and general topics. Also, very apparently need New World examples! 

     

    Stabilizing a wine refers to the removal of unstable elements to prevent spoilage, including unintentional re-fermentation and excess precipitation, from occurring post-bottling. There are several winemaking techniques that can be employed in order to stabilize a wine: decanting and racking; cold stabilizing; filtering; chemical additions; and aging pre-bottling. This essay will explore these methods and the reasons why they are implemented.

    • Decanting and racking
      • Decanting can be implemented at multiple stages throughout the winemaking process, allowing unstable elements, including lees, MOG, and precipitates, to naturally fall and settle at the bottom of a vessel. 
      • Racking refers to the process of running the clean wine from one vessel to another in order to remove the precipitates manually after the clean wine has been remove; often, the clean wine is then returned to the vessel.
      • Examples:
        • At La Mission Haut Brion, winemakers rack their barrel every 3 months, using gravity to run the wine out of barrel, specifically into a wine glass over a candle until the light shows that the liquid has become cloudy. At that time, they stop running the wine and filter the remaining sediment, reclaiming any additional wine. They prefer to remove sediment regularly, but they vary the frequency based on vintage and how much O2 the wine can take. (Also: they note this helps color stability)
        • Erni Loosen in the Mosel leaves his dry wines for 12 months on the lees without racking to preserve a reductive environment and stabilize his wines through exposure to the mannoproteins released by the yeast cells (e.g. longer lees contact leads to greater potassium bitartrate stability; see: cold stabilization)
    • Cold stabilization
      • Cold stabilization occurs when the wine in tank is dropped to freezing temperatures in order to induce the formation and dropping of tartrates, crystals which may form in the future due to tartaric acid precipitating in bottle at cooler cellar temperatures. The formation of these crystals is more common in higher pH wines. The process is done due to more aesthetic reasons and consumer concerns (look like pieces of glass).
      • How it’s done: Cool wine to -1 to -4 degrees Celsius for minimum 2 weeks; can add cream of tartar to speed the precipitation process, but it requires the recovery the crystals. Note as well the high cost of electricity in large quantities, which can account for up to 25% of a winery’s electricity costs.
      • Examples:
        • Widely practiced in traditional method sparkling wine production after blending and before the liqueur de tirage is added. (Multiple examples of grandes marques, etc.)
        • Bulk wine example?
    • Filtration
      • Filtration is the process by which large particles are removed from the wine by passing through a material, where a pad or a thin membrane. Often times, a fining agent like bentonite will be added to the wine first to cause invisible protein colloids to precipitate and thus be large enough to be removed.
      • Examples:
        • Quercetin precipitate from a grape low in anthocyanins from a hot vintage (Sangiovese and Nerello Mascalese – use a fining agent to cause the molecules to precipitate pre-bottling, then filter out
    • Chemical additions/SO2
      • SO2 additions in either gas or liquid form can bind to unwanted acetaldehyde aromas that may have formed during MLF (or be used to block it) and can help prevent oxidation during steps like racking and filtration. They can also kill off unwanted microbes in the wines, especially at the final step before bottling.
      • CMC? Mannoproteins?
    • Aging pre-bottling
      • Extended aging in cask before bottling will naturally allow for exposure to oxygen in small amounts; with more time the wine spends in wood, intentional aromas of oxidation may occur and will act like a preservative.
      • Examples:
        • Marco de Bartoli’s perpetual solera in which wine is added each year for the production of his Vecchio Samperi. The large oak casks are only half filled, causing intentional oxidation of the wines.
        • Madeira: canteiro — natural aging oxidative process where small barrels are placed in attics without temperature control, allowing the wines to concentrate over time.
        • Other fortified, white rioja, etc.
  • Hi Sarah/Sabrina,

    When I did this for the S1, I did quickly mention electro dialysis, CMC and mannoproteins. For the RS aspect I mentioned the need to sterile filter and gave the SO2 levels but style.  A bulk example of a producer that does cold stabilization and not CMC, even though it would be cheaper, is The Wine Group in CA.  For another domestic example, Ch. Ste Michele uses electrodialysis on all their whites.  

    Also, save yourself time on this by being really clear on where paper 3 starts and ends: Racking is Paper 2.  Paper 3 starts with cold stabilization, or whatever methods are used for tartrate stabilization.  The only filtration is the final filtration pre-bottling.  I think this is confused when we go back to early questions before the paper boundries were so solid. 

    Stabilization before bottling I understand as tartrate, microbial, and metal stability (essentailly chemically and biologically stable and fault free.)  

    I am emailing you both my other outline because the formatting gets destroyed when I try to copy it in her.

  • Great point about P2 v. P3 . See? Up to my neck in weeds. The Wine Group is great; much appreciated. I’ll check out your outline as well (I know; I’ve had to reformat so many times on these threads!!)

  • Hi . Good news and bad news. There's info in here that is out of the scope of the question. This means that you can free up some time to focus on the relevant topics in here!

    I'd break this question down into three 4 major categories - tartrate stability, protein stability, colloidal stability, and microbial stability. When I did this in the S1, I addressed the "why" in the introduction/conclusion, and focussed each paragraph on the different "hows".

    No need to include racking since that's more in the scope of P2. You've made an interesting point of about oxidation providing stability in fortified wines. I'd steer clear of that one too since it's not mentioned in the examiner's report.

    For cold stability - you can include some of your additions examples here. CMC and other gum products are used for cold stability but don't need to traditional cold to work. You can also include your ion exchange electrodialysis example in here so you've hit three methods. I bet you could find some diverse global examples for this as well - traditional cold in boutique Champagne vs ion exchange at larger facilities. 

    You mention proteins under filtration, but even a sterile filter won't filter out hazes - a giant colloid of protein is still much smaller than a bacteria. I'd address protein stability on its own with bentonite. I struggle to have a fleshed-out paragraph here since bentonite is still the main way that wines are proteins stabilized around the world.

    I'd include your SO2 addition info in a microbial stability paragraph with your filtration info.

  • 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).

  • Hi all

    Here are my notes for these questions. To keep things manageable, I tried to focus on the "how" since this is explicitly called for in both questions. I didn't put these notes together in an hour. So keep in mind that this is probably too much information for an essay.

    Stability definition: the removal of components from wine to ensure that no undesirable physical or sensory properties develop for a given period of time under a given set of conditions.

    Cold stability definition: the ability of a wine to resist the precipitation of tartrates (Dr. Eric Wilkes, AWRI)

    Protein stability definition: the ability of a wine to resist the denaturation and aggregation of grape proteins

    Microbial stability definition: the removal or inhibition of microbes in wine to avoid refermentation

    WHY

    • Removal of calcium and potassium tartrate which can precipitate in bottle
    • Removal of proteins which can form haze in bottle
    • Removal of microbes (or microbial nutrients) to avoid refermentation in bottle
    • Crowded marketplace – 60k SKUs in USA alone
    • Consumers expect brilliant clarity in most wines

    HOW

    Tartrate

    • Refrigeration
      • Wine is chilled to close to freezing and held at temperature for 2 weeks. Potassium tartrate is less soluble at colder temperature, will precipitate out of the wine. Process can be sped up with “contact process” of added potassium bitartrate powder which provides a nucleation point for crystal formation.
      • This process is more common at smaller wineries because it only requires glycol chilling. Energy intensive but doesn’t require the investment in new technology. This process does not guarantee stability.
      • Example: (thanks Anne) The Wine Group in Madera, USA uses traditional chilling for cold stabilization.
    • Ion exchange
      • Wine is passed through a resin column where potassium ions are swapped for sodium or hydrogen ions. Potassium tartrate cannot form because potassium is not present in wine.
      • This process guarantees stability but may impact sensory – sodium may have a soapy impact. Hydrogen may be overly acidic.
      • Example: 14 Hands in Prosser, WA, USA uses STARS electrodialysis on all wines. It is faster and less expensive than cold for their high volume products.
    • Crystal growth inhibitors
      • Block potassium bitartrate crystal nucleation and growth by binding to one of the crystal faces, therefore preventing further growth and precipitation of visible crystals.
      • Less impact on wine pH/TA than cold or ion exchange. Labor and time savings. Lower energy that traditional refrigeration.
      • Metatartaric acid – polymer of tartaric acid formed by heating. Wine should be protein stable before adding. Most effective at preventing precipitation in many wines (Eric Wilkes, AWRI). Product example: Laffort POLYTARTRYL®
      • Carboxymethylcellulose (CMC) gum – polymer of cellulose with carboxymethyl groups. Cannot be used on red wines or wines that are not protein stable, will form haze. Can cause color precipitation. Are not effective for calcium tartrate stability. Product example: Laffort CELSTAB®
      • Yeast mannoproteins – derived from yeast cell walls. Contributes to both tartaric and colloidal (tannin/color) stability of wines. Product example: Laffort MANNOFEEL®
      • Example: College Cellars in Walla Walla, WA, USA uses CMC gum on a Muscat wine which turns from harvest to bottle in one month. Small school/winery does not have time for traditional cold or money for ion exchange.

    Protein

    • Protein hazes form when proteins denature (change shape). The denatured proteins aggregate and form a haze.
    • Protein hazes are formed by grape derived proteins. Proteins derived from yeasts (lees contact etc) do not contribute to haze formation.
    • Bentonite addition
      • Bentonite is made from weathered volcanic ash. When hydrated, it “opens” to expose positively charged layers of ions which bind to negatively charged proteins.
      • Disadvantage: large amount of wine loss in “lees”, potential flavor stripping
    • Enzyme addition
      • Addition of enzyme which breaks down haze-causing proteins in conjunction with flash pasteurization. Enzyme has been approved for winemaking in Australia and New Zealand.

    Microbial

    • A wine should have a low microbial load before bulk transport or bottling.
    • The majority of the worlds wines by volume are transported in bulk and bottled in port. Change in temperature due to equatorial transport can lead to microbial bloom if wines have not been rough filtered down to a low level, and do not have sufficient preservatives including free sulfur dioxide.
    • Additionally, wines will need to be very close to microbially stable before attempting sterile filtration at bottling. Excessive microbial load will foul a 0.45 micron nominal filter. To achieve a low microbial level, wines can be sequentially filtered through filters of increasing tightness including diatomaceous earth filters, pad filters, and cross flow filters.
    • Other options for microbial stability include use of dimethyldicarbonate ("velcorin"). However, this is more common at bottling and out of the scope of the question.

    Additional stability concerns

    • Phenolic stability is a relevant issue too. Quercetin instabilities can occur when quercetin levels become excessive. This has become an issue is some Sangiovese based wines from Central Italy. According to Dr. Steve Price, ETS Laboratories, these instabilities can be mitigated by blending with high anthocyanin wines. If the quercetin colloid becomes too large and precipitates out, the wine can simple by racked off of the sediment and filtered.
    • Metal stability – more common in wines with high levels of copper sulfate from vineyard or use of copper fining in winery. 0.2 mg/L of Cu will likely throw a haze (according to Gordon Burns, ETS Laboratories). Metal haze or “casse” of metal salt looks like blue sludge.


    Further reading: Cold Stability, CMCs and other crystal inhibitors. Dr. Eric Wilkes, Australian Wine Research Institute.