Plant-Based Alternative Fining Agents

Historically, some pretty gross things have been used in wine production, especially in terms of proteinic fining agents, and there is evidence to suggest that residual components of the fining process can persist in wine in some cases (Maury, 2019). The first to come to mind is ox blood (the active component of which is the protein hæmoglobin), followed shortly by fish offal (isinglass), and the byproducts of boiled animal carcasses (gelatine). There are of course more benign animal-based products that are still routinely used by some winemakers in wine production such as egg white (mainly ovalbumin) and skim milk (casein), although these proteins too can be allergenic if present at low levels and a label declaration of their usage will be mandated from 2024 for the EU. These fining agents have been discussed previously (Bowyer 2008, Parts 1 & 2) in terms of their physical, chemical, and organoleptic characteristics. The use of somewhat unsavoury fining agents such as these was mandated at the time by three major factors: these processing aids were both cheap and readily available, functioned effectively and because no animal-free alternatives existed. No real consideration was given to market requirements in terms of wine processing aids and additives, and it is not uncommon for wine consumers to be very surprised (and more than a little concerned) to find that products of this type have been used in the production of the beverage they were hitherto enjoying in blissful ignorance. A similar sphere of concern surrounds the use of PVPP (polyvinylpolypyrrolidone) by some wine consumers (and a growing proportion of winemakers) given that this is a microplastic, and is thus detrimental to the best spaceship we have – planet Earth.

Fast forward to current times and things have moved on a bit. In this article we will explore some options for allergen-free, vegan-friendly, and microplastic-free fining agents, and the depth of development required to deliver effective products to market.

Plant proteins

There are typically two offerings when it comes to plant proteins for juice or wine fining: potato or pea (wheat protein is also permissible in the OIV Codex, but since some people are sensitive or allergic to gluten this is not likely to be used by manufacturers). Of these two proteins, the pea proteins tend to be the more organoleptically benign due to the earthy smell intrinsic to potato protein. Pea proteins also tend to be easier to resuspend in water, which can make their use in a winery environment more practical. That said, not all pea proteins or potato proteins are equal, with substantial variations in the quality and characteristics of raw materials, and in order to provide a commercial product of consistent quality and characteristics significant investment must be made in terms of raw materials analysis and batch selection. To explain this, we will delve into the processes involved in oenological pea protein-based product development.

Aspect

Aside from the usual oenological processing aid/additive requirements of solubility, moisture/nitrogen/ash and heavy metals content, any proteins used in wine production must be fit for human consumption (obviously), even though as processing aids they technically do not remain in the wine to any great extent. A potential product source must also be scrutinized for the presence of any microorganisms and other undesirable residues. Critical parameters examined in the raw pea protein materials are protein content (%), molecular weight and solubility, with the parameters of lower importance being aspect (appearance/odour) and pH. Table 1 shows some examples of the solid and aqueous dispersions of the commercial product Greenfine Must and two raw material candidates.

Table 1: Greenfine Must and two potential raw material candidates in both solid and suspended states, illustrating the variation observed in raw materials and the need for continual batch analysis with respect to several parameters.

Protein content

Obviously, since these products are used to remove phenolic compounds from juice or wine the protein composition and content are of high importance. Figure 1 depicts analyses of the protein contents four commercial products and six raw material candidates. Significant variation exists in the percentage of soluble protein of all samples, which emphasises the extreme importance of rigorous raw material scrutinization. Additionally, a commercial product must be as consistent as possible to ensure its reliable performance in the winery environment.

Figure 1: A comparison of the protein content of four commercial pea protein-based fining products and six raw material candidates.
Molecular weight distribution

Aside from soluble protein content, the composition of the protein is of paramount importance, as this is what largely determines the relative reactivity and fining action on phenolic materials in juice and/or wine. Gel electrophoresis is a simple and very effective technique to characterise the protein molecular weight distribution of raw material candidates. Since proteins carry a charge according to their amino acid composition and the pH of their environment (except at the protein’s isoelectric point, where the overall charge is neutral), protein fragments will migrate in an applied electric field according to the function of both their molecular charge and molecular weight. Standard molecular weight protein fragments can be used in such characterisations, as seen in the electrophoretogram shown in Figure 2, which shows the molecular weight distribution of three raw material candidates.

Raw 1 and Raw 3 show similar protein molecular weight profiles, whilst Raw 2 is quite different, with a larger proportion of smaller protein fragments. These differences are largely a result of raw materials production variances and serve to illustrate the importance of raw materials analysis to ensure consistency in commercial products.

Figure 2: An electrophoretic analysis of the protein molecular weight distribution of three raw material candidates.

Heat stability

Since plant-based fining agents can be used in both the juice/must and wine phases, it is important to ascertain that they will not contribute to wine protein instability upon heating. This is simply determined by addition to a stable wine at 500 ppm followed by a heat stability test, the results for which are seen in Figure 3. The control wine had no protein addition made. Raw material candidates 1, 2 and 4 were deemed unsuitable for commercial use.

Figure 3: The change in NTU observed in wines after the addition, mixing and then removal by filtration of 500 ppm of each product and subsequent heating to a previously protein stable wine.

Colour impact and phenolic removal

Phenolic removal is a key characteristic of any proteinaceous fining agent, and this is facilitated chiefly by protein molecular weight and charge density. Figure 4a illustrates the electrophoretic profiles of some gelatines, egg white, yeast protein and pea protein as compared with molecular weight standards. Figure 4b indicates the approximate molecular weight distributions of these fining agents. For example, roughly half of egg white is ovalbumin, which is the ~ 43 kDa fraction, with lesser amounts of ovotransferrin (~ 76 kDa) and lysozyme (~ 14 kDa; Iwashita et al, 2015). Gelatine products vary considerably in molecular weight composition depending on the source animal and extent of hydrolysis applied during production, with larger fragments requiring hot water to dissolve. The electrophoretic analysis indicates that pea protein on its own is not necessarily a suitable replacement for hot-soluble gelatine, for example, as the protein molecular weight profiles are too different, not to mention the amino acid compositions.

Figure 4: (a) Molecular weight fractions of selected fining agents as compared with standards. (b) A generic representation of the main molecular weight fractions of various fining agents. GL = Gélatine Supérieure de Russie ; GSF = Gélatine Soluble à Froid (Géliclar) ; GSC = Gélatine Soluble à Chaud (Gelfine); Pea = Pea protein

Commercial product formulations

Given the above information, it should now be easy to understand the complexities of creating vegan-friendly/non-animal based/non-allergenic fining agent alternatives to traditional animal-based fining products. It should also be clear that whilst pea protein alone is a suitable alternative to ovalbumin, for example, it cannot hope to provide the same overall fining action as gelatine, which tends to be both aggressive in action and broad spectrum in function and is also quite variable depending on production factors as noted. Moreover, increasingly winemakers are seeking to avoid the use of PVPP due to its microplastic nature, yet PVPP is a rather specific product in terms of target phenolics, a derivative of its chemical structure and polymeric cross-linking (Bowyer 2008b; Waterhouse et al, 2016). Some winemakers also simply do not like the concept of PVPP as it is a petrochemical product, pollutes the environment with a very long half-life and poor versions can be contaminated by residuals of the monomer, evident in a strong chemical odour in the dry product.

For these reasons the Greefine product range is comprised of five variants (currently), with formulation as indicated in Table 2. Greenfine Rosé (formerly Greenfine Mix) is formulated specifically for white/rosé fining, whilst Greenfine X-Press is perhaps the best substitute for gelatine, being more broad-spectrum in its phenolic removal. Greenfine Intense does not have a strong phenolics removal capacity, being formulated rather for removing oxidative browning and associated characters through its decolourising carbon component. In some of these products calcium bentonite is a component used to aid flotation and/or clarification.

Table 2: The Greenfine product range characterised by composition, impact on wine structure/colour stability/vegetal notes/oxidative characters, substrate and recommended dosage.

Greenfine Nature

Perhaps the most interesting Greenfine variant, and certainly the newest, is Greenfine Nature, which was developed collaboratively recently ago with oenologist Gilles Baude, head oenologist at Provence Oenology, who expressed concern about the use of microplastics. Gilles also required a product suitable for vegans and organic wine production, and it also had to be functionally efficient at phenolic removal. Through trials spanning several vintages Lamothe-Abiet was able to formulate a commercial product that functions in a similar way to PVPP, yet contains no allergens, is vegan-friendly, suitable for organic wine production and contains no microplastics.

Greenfine Nature is comprised of pea protein, a highly specific inactivated yeast fraction and calcium bentonite. The yeast fraction adds a small protein (~ 10 kDa) that is able to bind the most reactive phenolics in a similar manner to PVPP, reducing wine astringency and bitterness. This peptide fraction also confers a very slight sucrosity to the wine, making it look more fruit-forward rather than sweet. In a comparative tasting (Figure 5) of wines where PVPP and Greenfine Nature were added to a common juice (2022 Provençal Grenache rosé) at 600 ppm strong differences were observed. Compared with PVPP, Greenfine Nature delivered more volume, length, aromatic intensity and freshness.

Figure 5. The comparative tasting results from wines made with PVPP and Greenfine Nature at the same dosage rate of 600 ppm added to the same juice.

An analysis of impact on wine colour (Figure 6a) between PVPP and Greenfine Nature shows better overall colour intensity from Greenfine Nature, stronger purple hues (A620) and a similar impact in the red region (A520), with more intensity in yellow (A420). Figure 6b illustrates the overall phenolic impacts between the two fining agents, along with the specific impact on phenolic acids, which are susceptible to oxidation and subsequent brown pigment formation.

Figure 6: The relative impacts of PVPP and Greenfine Nature in terms of colour (a) and phenolic removal (b) in a 2022 Provençal Grenache Rosé at 600 ppm.

Greenfine Nature was also investigated for its organoleptic impacts on wine aromatics via SPME/GCMS analysis of thiols and esters in the same 2022 Provençal Grenache Rosé compared with PVPP. Both fining agents were added to the same juice at a rate of 600 ppm to the juice and all other parameters in wine production were identical. The analyses (Figure 7a/7b) indicate similar aromatic impacts on the wine for both fining agents, with Greenfine Nature showing less impact on thiols and a slightly higher impact on esters. There is a notable reduction in 4MMP (box/cat pee) with Greenfine Nature application, which some winemakers view as a positive, as it serves to reduce green aromas and to highlight rather the citrus notes in the wine.

Figure 7. Ester (a) and thiol (b) analyses for a 2022 Grenache rosé treated with 600 ppm of PVPP and Greenfine Nature at the juice stage. Data are reported as aromatic index (i.e. concentration/perception threshold).

Summary

Options now exist to avoid the use of animal-based fining agents through the use of new plant-based products. It is even possible to eliminate the usage of PVPP to arrest the contamination of the environment with microplastics, after considerable collaborative efforts between an oenologist and Lamothe-Abiet. The effectiveness of these new fining agents varies according to their respective formulations and phenolic targets, and trial work at the winery is advised in determining the correct product and rate to use. The extensive characterisation of products in the Greenfine range discussed in this article lays the foundation for the development of future new product formulations to provide effective treatments for new market requirements.

By Paul K. Bowyer & Galdric Nogues

References

Bowyer, P. K. (2008a) Part 1: Proteinaceous fining agents, The Australian and New Zealand Grapegrower and Winemaker, June Issue, 55-63.
Bowyer, P. K. (2008b) Part 2: Non-proteinaceous fining agents, The Australian and New Zealand Grapegrower and Winemaker, July Issue, 65-71.
Kazuki Iwashita, Naoto Inoue, Akihiro Handa, and Kentaro Shiraki, Thermal aggregation of hen egg whites proteins in the presence of salts, Protein J. (2015), 34(3), 212–219.
Maury, C., Sarni-Manchado, P. and Cheynier, V. (2019) Highlighting protein fining residues in a model red wine, Food Chemistry, 279, 272-278.
Waterhouse, A. L.; Sacks, G. L. and Jeffery, D. W. (2016) Understanding Wine Chemistry, John Wiley & Sons (UK), 336.

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