Growing & Winemaking

 

Cold Stabilization and Malolactic Fermentation

June 2018
 
by Richard Carey
 
 

Two products that could help winemakers produce significantly better wines should prompt wineries to seek approval from the Alcohol and Tobacco Tax and Trade Bureau (TTB), which has not fast-tracked these items.

The first is Zenith, a colloidal material that will cold-stabilize both white and red wines permanently. Enartis developed the product and introduced it at this year's Unified Wine & Grape Symposium.

The second is a bacteria, Lactobacillus plantarum, that can consume malic acid to finish malolactic fermentation (MLF) more quickly and completely and with fewer side metabolites. L. planetarium is approved internationally for use in wine and in the United States for beer, but not for wine.

Zenith Uno and Zenith Color
Zenith Uno is for white wines, Zenith Color for red wines. White wines, unlike red ones, must be heat-stabilized prior to addition. K-polyaspartate (KPA) is the functional compound of the new colloidal cold-stability agents for use in wine. The chemical process polymerizes L-Aspartic acid into K-polyaspartate (KPA).
 

More than 14 research and university entities have been involved in research to validate the functionality of this compound in cold-stability. These institutions include universities in France, Italy, Spain, Portugal and Greece.

Tartaric-acid crystallization occurs in wine because tartaric acid has the ability to remain temporarily in solution even though it is above its saturation point in an alcohol-water solution. This state is commonly known as supersaturation. The tartaric acid will crystalize and produce glassy-looking crystals in wine when two ions of tartaric acid come close enough to each other. Most frequently, there is some particle (usually potassium bitartrate or KHT) that acts as a nucleation point, causing the ions to exceed the saturation point and crystalize. These ions form the first crystal, which can start a chain reaction to create more crystals. As a colloid, KPA envelops the tartaric acid anion and prevents the ions from getting close enough to precipitate.

In trials comparing the most common methods of achieving cold stability, KPA was more efficient as compared to other methods of cold stability. The standard method measures µS, as a determination of conductivity in wine. This is the determining factor in measuring the tendency for cold stability and is defined as a drop-in conductivity of less than 5%. The test wines were well above the standard threshold for cold stability, which indicates that the solution they were in was more conductive than those that were cold stable.

    Carboxymethylcellulose (CMC) is the current colloidal material used extensively to cold-stabilize wines. It does not quite lower the conductivity for all wines sufficiently below the threshold to maintain a guaranteed cold-stable wine. MTA (a commonly known polymer of tartaric acid) is a material that wineries have used to obtain cold-stability. Zenith has been shown to be better than MTA and equal to KHT.

Colloidal products such as CMC have a propensity to remove color from wine, a vexing problem for winemakers. Figure 1 shows an application trial in which CMC and Zenith Color were added to samples of Shiraz and then held for six days at -4° C. Additional amounts (possibly 50% or more) of CMC would be necessary to get close to cold-stabilization, and the wine still would not achieve the same color level as a wine treated with KPA.

The CMC drop in color shows the degree to which color is removed from red wines when cold-stabilization procedures are introduced. When CMC is added, the material entraps the anthocyanins and might reduce or remove much of the color from red wines. In contrast, Zenith has virtually no color loss. The use of Zenith would allow wineries to lower the cost of production for sweet red wines, to market all red wines more quickly and do so without the danger of future color loss or tartrate formation.

Cold-stability treatments should give wineries the assurance that once a wine is tested as cold-stable (Figure 2), the treatment will continue to work over time. Tartrate stability is a statistical issue, defined by the chance that two ions can come together in an environment where they are locally above saturation. Crystallization is a lower-energy state waiting for a trigger. KHT is the enabling molecule that can trigger crystal formation and reduce the tartaric-acid molecule population to the probability of crystal formation approaching zero.

Stabilab is an instrument that follows the process of conductivity change. Its algorithms measure the asymptotic conductivity curve that changes with increasing amounts of time and/or KHT additions. It is a very accurate - but expensive - solution, and ultimately the winemaker chooses how far down that curve is comfortable enough for a commercial winery.

The "rule of thumb" for KHT addition generally has been defined as 4 g/L KHT at either 0° C or -4° C as the end point where conductivity does not change by more than 5% after addition of KHT to the wine. The requirement that the wine be lowered to these temperatures while the process unfolds is time-consuming and labor-intensive. KHP addition is tested manually by mini contact test or the automated Checkstab and uses a 3% drop in µS.

CMC was found to prevent crystallization with a simple liquid addition and stirring. Its mechanism of action, and that of KPA, can be likened to replacing the "empty" space between the tartaric-acid molecules in traditional cold-stability action to filling the empty space with Nerf Balls. In this situation, two tartaric acid molecules can't get close enough together to crystalize because CMC and KPA molecules surrounding tartaric acid act like Nerf Balls to prevent them from getting close enough to crystalize.

Whereas both molecules envelop the tartaric-acid anion, the KPA product envelops its target more tightly and thus protects it more completely from precipitation over time (Figure 3).

Adding anything to a wine just before bottling can be a risky endeavor. Winemakers need to know that nothing will change the filterability of the wine being packaged. Fortunately, KPA does not affect the filterability of wine.

There are a number of secondary benefits to using KPA. A strong trend in the wine industry supports the use of products that are more sustainable in terms of energy, impact on the environment and the consumption of other resources. Zenith (KPA) and CMC are shown to be close to each other as more sustainable products from a total energy-consumption standpoint.

The reduction of water consumption by wineries is another critical component for sustainable product use. The industry has widely different levels of water consumption, in part depending on the cold-stabilization process used (see Figure 4). By far the worst consumer of water during cold-stabilization is electrodialysis, which has been adopted by many larger wineries because of the great energy savings over traditional cold-stabilization methods. Both CMC and KPA are among the lowest in water consumption.

It should be noted that while CMC and KPA are low in energy and water consumption, only KPA is more certain to provide permanent cold-stabilization.

Finally, a cost-of-use comparison shows that this product might help change how wine is produced. Only the KHT method is close to colloids when it comes to the total cost to achieve cold-stability in wine.

Several wineries have tried Zenith, from very large ones such as Arterra Vins Canada in Ontario, Canada to small Eastern wineries such as Mount Felix Vineyard & Winery in Havre de Grace, Md. Others include Precept Wine Brands in Seattle and Brick & Mortar Wine Group in Healdsburg, Calif.

Enartis, and the wine industry, recently learned of one regulatory step toward approval. The FDA has indicated it will accept KPA as a GRAS ("Generally Recognized As Safe") product.

Although the above information has been submitted to TTB, the agency has not given final approval of this product. Apparently, TTB would like to hear from industry people that winemakers want to use this product before the agency will give its approval. I suggest that wineries send their comments and urge TTB to approve Zenith for use in wine production.

Lactobacillus plantarum
There is a wealth of active research on alternate organisms to Oenococcus oeni for conversion of malic acid into lactic acid. However, some of the reported literature has been inaccurate in its interpretation.

Among many different strains of LAB (Lactobacillus Bacteria spp), L. plantarum is one of the better organisms for acid conversion, especially for higher pH wines (above 3.4). In addition, its diverse and complex metabolic pathways provide complexity to wines, according to Lucio et al.1

The research on this organism addresses three methods: inoculation of LAB into must pre-alcoholic fermentation, co-inoculation and addition post-alcoholic fermentation. Despite the inference by Lucio et.al. that pre-alcoholic fermentation is the preferred method, in my discussions with colleagues involved in current research, there seems to be a changing consensus that co-inoculation might be the better method. This conclusion developed and evolved as several strains have been identified and selected that are better suited to this production environment. These strains are more complete in their metabolism of malic acid into lactic acid, especially in high-pH wines.

Malolactic-fermentation organisms have two types of metabolic pathways for basic respiration: heterofermentative and homofermentative. O. oeni is heterofermentative, meaning it will use multiple energy sources for survival, including hexoses. L. plantarum, in contrast, is not able to metabolize hexoses, which means that O. oeni can produce acetic acid but L. plantarum will not.

LAB organisms have been saddled with another misconception3,4: That they produce biogenic amines and carbamates, neither of which are desirable in wines. Biogenic amines are compounds responsible for causing headaches as well as noxious aromas and flavors. No producer wants putrescine or cadaverine in its wines, and consumers who are sensitive to histamine or tyramine don't want them, either.

Through research, we now know that certain LAB organisms, including L. plantarum, do not produce biogenic amines or carbamates, but actually degrade and remove those substances from the wines in which they are used for MLF.2 It also has been found that S. cerevisiae and O. oeni are active producers of acetic acid, biogenic amines and carbamates. Often in stressed fermentations S. cerevisiae produces significant quantities of biogenic amines. The carbamates might be produced by certain LAB, but not by L. plantarum.

Unfortunately, there is a lot of old information online that has not been updated. One example is the University of California, Davis Department of Viticulture and Enology's website. In their descriptions of various bacterial species, the site specifically mentions that there is concern about the L. plantarum organism as a possible producer of acetic acid, biogenic amines and carbamates. This mention might be one of the reasons TTB has not acted on adding L. plantarum to the list of approved organisms.

Similar to the Zenith product, perhaps the only way L. plantarum will be allowed for use in wine production will be if the industry petitions TTB. Those wineries or winemakers who would like to see how this organism will affect their wine production can obtain limited samples of L. plantarum from Lallemand. If a winery decides to try this organism, Lallemand requests that they co-inoculate with yeast. In addition, the winery must understand that it won't be able to sell wine treated with L. plantarum, at least in the short term.

It should be noted that winemakers should not go to ATCC to purchase off-the-shelf cultures because they likely will be dissatisfied with the results. Companies such as Lallemand that provide yeast specifically for winemaking have found that L. plantarum must be grown in a specific culture solution to stabilize it and tune its tolerance for wine.

The fact that L. plantarum is approved for use in beer, but not wine has led to a "Call to Arms" to petition the TTB to allow the use of Lactobacillus plantarum as an alternate organism to O. oeni. If readers agree with the proposition, they can write to TTB at the address below to ask not only for the ability to trial-test this organism, but for its experimental use and sale in the production of wine. Despite repeated attempts, TTB has not returned calls requesting answers about their reasoning for not allowing its use in wine. Lallemand staff members said they have had the same experience.

If readers agree wi th the proposition, they can write to TTB at Alcohol and Tobacco Tax and Trade Bureau, 1310 G Street, Washington, DC 20004 to ask not only for the ability to trial-test this organism, but for its experimental use and sale in the production of wine.


Richard Carey, Ph.D., is a wine consultant in Lancaster, Pa., and owner of Tamanend Wine, Inc.

 
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