Vine and wine innovation watch: The use of carrageenan in calcium tartrate and protein stabilisation of wines

Introduction

Calcium-induced instability has emerged as a significant problem in bottled wines due to compositional changes caused by global warming. The appearance of calcium tartrate (CaT) crystals at the bottom of the bottle negatively affects wine acceptability, and current stabilisation strategies that are effective in removing potassium bitartrate (KHT) crystals are often ineffective against CaT crystals.

Tartrate ions (T^2-), resulting from the dissociation of both carboxylic groups of tartaric acid, have a pKa2 of 4.34 in water and are typically present in low amounts in wine, which has a pH range of 2.8 – 4. Recently, research showed that the pH of Languedoc red wine has increased from 3.50 to 3.75 over 35 years. The ongoing climate change is causing a shift in the dissociation equilibria of acids in wine, leading to an increase in T^2-. In addition, global warming increases the amount of calcium ions (Ca²⁺) in wine. This is because the increasing temperature results in hydric stress and changes in the water equilibrium in grapes. Researchers have found that calcium levels increase seven-fold in stressed plants, likely due to calcium’s crucial role in regulating water absorption and water flow in the plasma membrane of plant cells during drought. These factors contribute to the increased likelihood of CaT precipitation in bottled wine, which can impact consumers’ perception and potentially lead to a decrease in the value and price of wines.

A concentration of 60 – 80 mg/L of calcium in wines is usually considered at risk of instability and precipitation, but this is not the only factor determining wine stability. Preventing CaT precipitation is challenging. Although ion exchange resins and electrodialysis are effective, they can affect wine’s chemical and sensory properties. While potassium poly-aspartate (KPA) is an available stabiliser that can prevent the precipitation of KHT, it is ineffective in preventing CaT precipitation. Currently, seeding with micronised CaT is the most effective approach for CaT stabilisation, but it is expensive and time-consuming. Therefore, research is focused on discovering new potential stabilisers that can reduce the likelihood of CaT precipitation.

Carrageenan

Carrageenan is a hydrocolloid derived from red seaweeds, characterised by disaccharide repeating units consisting of 3-linked-β-d-galactopyranoses and 4-linked-α-d-galactopyranoses. Due to its gelling properties, carrageenan is widely used in the food industry and pharmaceutical applications as a thickener and stabiliser. The chemical composition of carrageenan varies based on the number of sulphated groups present in the disaccharide repeating unit, with the most used forms being kappa-carrageenan, iota-carrageenan and lambda-carrageenan, which have one, two and three sulphated groups, respectively.

Carrageenan can bind different types of ions, particularly K⁺, Ca²⁺ and Mg²⁺. Specifically, kappa-carrageenan and lambda-carrageenan exhibit strong affinity for K⁺ and Ca²⁺, and their association is primarily driven by ionic bonding between the ions and the sulphated groups. The presence of a 3,6-anhydrogalactose group can cause Ca²⁺ to exist in an electrostatic state that stabilises the helicoidal structure of the hydrocolloid. Based on this premise, a research study aimed to prevent the formation of CaT crystals and subsequent precipitation by adding a commercial mixture of kappa-carrageenan and lambda-carrageenan to wines before protein stabilisation with sodium-bentonite.

Experimental layout

• Four white and two rosé wines, which exhibited varying CaT and KHT stability levels, were analysed.
• Carrageenan was prepared by dissolving and homogenising it in distilled water using a magnetic stirrer until it was completely soluble.
• Next, carrageenan was added to the wine samples at concentrations of 25 g/hL and 75 g/hL, and the mixture was continuously stirred for three days at room temperature.
• After three days, 50 g/hL of sodium bentonite, soaked in water for 24 hours, was added to the treated wines and kept in contact with the wines for four days at room temperature.
• All samples were examined on the third day after adding carrageenan and on the fourth day after adding sodium bentonite.
• The wine samples that did not receive the carrageenan treatment were controls. All treatments were conducted in triplicate.

Results

• All wines were CaT stable after adding carrageenans and sodium bentonite.
• Most wines were also protein stable, except for one that was still slightly unstable.
• Additionally, KHT stability was improved.
• The mini-contact test with micronised CaT seeds, DLS analysis and FTIR spectra confirmed that CaT stability was due to colloidal stabilisation rather than Ca²⁺ ions removal. The stabilisation mechanism may involve complexes involving carrageenan, calcium ions and proteins.
• Furthermore, the synergistic effect of bentonite may be attributed to the competitive adsorption of proteins, which results in the adsorption of larger amounts of Ca²⁺ ions by carrageenan.

Carrageenan and white wine protein stabilisation

Previous research in Australia has demonstrated that specific carrageenans can heat-stabilise wine at lower dosages than typically used for bentonite. However, the study’s authors also discovered that excessive amounts of certain carrageenan types, if not removed by filtration, could cause a haze in the wine.

A follow-up study, therefore, aimed to identify the most effective carrageenans for heat-stabilising white wine without causing negative side effects, such as poor filtration or inadequate heat stabilisation. The study screened a broad range of commercially available carrageenans and found that certain types, such as kappa-carrageenans in sodium or potassium salt form or a blend of kappa- and iota-carrageenans (containing up to 10% iota-carrageenans), were effective for this purpose. On the other hand, lambda-carrageenan or ‘pure’ iota-carrageenan did not heat-stabilise wines.

Portuguese researchers aimed to investigate the impact of kappa-carrageenan on protein stability and wine macromolecular composition. Their results showed that kappa-carrageenan reduced the content of pathogenesis-related proteins (thaumatin-like proteins and chitinases) and, consequently, protein instability in Albariño wines. Additionally, kappa-carrageenan was more effective than sodium and calcium bentonites in achieving this result.

Conclusion

Currently, carrageenan is permitted as a processing aid in winemaking only in Australia (Standard 4.5.1 Wine Production Requirements). It has not been approved for winemaking by the OIV or the European Union. However, as an environmentally friendly alternative to bentonite and a possible solution to manage climate change-induced calcium instability in wines, it may soon be approved for use in winemaking in the rest of the world.

References

• Gabriele Fioschi, Ilaria Prezioso, Luigi Sanarica, Rosanna Pagano, Simona Bettini & Vito Michele Paradiso, 2024. Carrageenan as possible stabilizer of calcium tartrate in wine. Food Hydrocolloids, Volume 157, 110403.
• Fernanda Cosme, Inma Arenas, Miguel Ribeiro, Luís Filipe-Ribeiro, Rafael Vilamarim, Elisa Costa, João Siopa & Fernan-do M. Nunes, 2023. Impact of fining with k-carrageenan, bentonite, and chitosan on protein stability and macromolecular compounds of Albariño white wine produced with and without pre-fermentative skin maceration. IVES Conference Series, OENO Macrowine 2023.
• Guidelines for using carrageenans to heat stabilise wine. Australian Grape and Wine Authority Supplement to Final Report. Project number: TWE 1301; Principal investigator: Dr Vanessa Stockdale; Research organisation: Treasury Wine Estates; Date: November 2016.

For more information, contact Karien O’Kennedy at karien@sawine.co.za.

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