International Oenological Codex (updated January 2019)
Key points related to oenological tannins: “Tannins are used to facilitate the clarification of wines and musts. Tannins must not change the olfactory properties and the colour of wine… Without prejudice to the provisions of paragraph 1, the use of oenological tannins changes the colour of wines to some extent, depending on their inherent colouring properties… The limits of these indices for an oenological tannin not to be considered as a colouring agent are:
+ 1.5 for yellow colouring properties (E420 1‰) and
+ 0.05 for red colouring properties (E520- E 420 1‰)”
'Tannins have the capacity to consume dissolved oxygen and... improve wine structure, mouthfeel, colour...'However, winemakers have used tannins to achieve various technological and quality goals for many years and researchers are discovering new applications for them.
41st World Congress of Vine and Wine:2018:19-23 November 2018:Vignault A 2018:New insight about the functionality of oenological tannins; Main results of the working group on oenological tannins
Key findings: In addition to the approved clarification application, tannins are also confirmed to have antioxidant activity, the capacity to consume dissolved oxygen and scavenge peroxyl radicals, can chelate iron, prevent oxidative damage, inhibit laccase activity, improve wine structure, mouthfeel, colour, stabilise red wine, lead to co-pigmentation and new pigments, eliminate reduction odours and control bacteria. Based on these studies, changes to the OIV Codex are recommended. Tannins from different sources have varying activities.
'It protects wine colour'Below is one of the studies involved in the project above, a joint effort between researchers from Spain and France using grapes from Tarragona, Spain.
Oeno One:2019:53-1:Vignault A 2019:Impact of enological tannins on laccase activity
Key findings: All of the oenological tannins used in the study inhibited laccase activity (issue caused by Botrytis cinerea infection, leads to browning of white wines and oxidasic haze in red wines) and protected wine colour.
Here is a study from Italy on the efficacy of sulphur dioxide, glutathione and chestnut tannins on controlling 'light struck' effect in wine:
41st World Congress of Vine and Wine:2018:19-23 November 2018:Fracassetti D 2018:Antioxidants for limiting the light-struck taste during the shelf-life
Key findings: All of the antioxidants in the study limited 'light struck' taste; lower levels of sulphur containing compounds – such as MeSH, DMDS and dimethyl trisulfide – were detected.
A study from 2011 in Australia looked at the use of tannin additions to deal with smoke taint.
AJGWR:2011:17-2:Ristic R 2011:The effect of winemaking techniques on the intensity of smoke taint in wine
Key findings: Tannin addition increased complexity, helping to mask smoke taint.
'Some products showed significant variation to the material designation of origin'In addition to picking the right tannin to achieve a goal, you also need to read the fine print related to the product you are looking to buy as this study from Australia points out:
AJEV:2017:Online December 2017:Li S 2017:Compositional Variability in Commercial Tannin and Mannoprotein Products
Key findings: Grape-based tannins varied widely in composition; some products showed significant variation to the material designation of origin.
Tannins of botanical origin, like any other plant-derived product, are susceptible to variation because of seasonal variability. Plant products are also, unfortunately, open to falsification. For laboratory detection methods refer to the OIV Codex and this study from Italy…
Food Chemistry:2016:In press March 2016:Malacarne M 2016:Verifying the botanical authenticity of commercial tannins through sugars and simple phenols profiles
Key findings: A combination of sugar and phenol analyses provided good results in identifying tannins of different botanical origins.
James Wright is an international viticulture and management consultant and author of www.vitisynth.com and the newsletter VitiSynthesis.