Tartrates – When diamonds are a deal-breaker….

After a long a gruelling day filled with meetings, deadlines, and unplanned mishaps you get home only to be greeted with dinner and a glass of wine shimmering in the candlelight. Instantly you feel the woes of the day melt away. You sit down, take a large swig of wine, but wait…. What on earth is this? Why are there pieces of glass in my wine???? You know diamonds can be your best friend, but surely this is not what was meant. Instantly you are back in conflict mode, swiftly dispose of the offending wine and jump to consult the internet on what these mysterious crystals may be (forgetting the dinner and candlelight on the way down the rabbit-hole). Naturally you only find articles that lead to more questions than answers and 20 minutes later you find yourself watching videos about cats…. Therefore, to prevent unsolicited cursing of an unsuspecting winemaker, let’s set the record straight on what these “wine diamonds” really are.

A well-made bottle of wine is a perfect marriage of different chemical components and flavours to yield a harmony of balanced flavours. However, irrespective of the care taken by the winemaker, every so often a bottle of perfectly fine wine can develop small crystals which resembles shards of glass. These crystals, affectionately referred to as wine diamonds, is one of the most common issues seen in winemaking and is caused by crystallisation of potassium bitartrate during storage. Although potassium bitartrate is a naturally occurring acid in wine grapes, these compounds are prone to crystallisation and precipitation due to its poor solubility in alcoholic solutions. Despite being harmless, their appearance often results in a decrease in customer appeal. Winemakers therefore often rely on removal of potassium bitartrate in a process known as cold stabilisation wherein the wine is cooled to -4°C and stored for 1-2 weeks. The reduced temperature promotes the formation and settling of potassium bitartrate crystals enabling their removal by filtration. However, in addition to being energy intensive and time-consuming, removal of the naturally occurring acids can also affect the colloidal stability and final flavour of the wine. Most recent advances in tartrate stabilisation have therefore been focussed on the inhibition of tartrate crystal formation.

An alternative to cold stabilisation is treatment with sodium carboxymethyl cellulose (CMC) which prevents tartrate crystallisation by exchanging the potassium of potassium bitartrate with a sodium ion from sodium-CMC. This method of ion-exchange results in an increase in the solubility of the natural tartrates. The sodium tartrate formed in this manner is extremely soluble (up to 779 g/L @25°C) when compared to potassium bitartrate (<8g/L @25°C) and therefore remains in solution during storage. Apart from being temperature independent, this method of tartrate stabilisation does not result in tartrate removal and therefore does not affect the flavour of the wine.

At IRS/Synercore we believe that solutions are local and “local is lekker”. We are proud to announce the development of ifaCel SW10 which is an affordable locally produced low viscosity solution of CMC (10%). Following lab-based testing in 2021, ifaCel SW10 was extensively tested at major wine farms in the Western Cape in 2022 and was proven to be effective in stabilisation of rosé and white wines.

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