Why does white wine turn pink?

This is the unexplained phenomenon that winemaker Anton Nel is currently exploring as part of his doctoral research project.

Nel, an Oenology lecturer in the Department of Agriculture on the Wellington Campus, commenced with his study last year and says his topic is relevant as this phenomenon is widely experienced in the wine sector, both locally and abroad.

“When white wines with the potential to pink are exposed to oxygen, the phenomenon known as pinking occurs. It is common in Sauvignon blanc, but also occurs in Chardonnay, Colombar, Chenin blanc and Viognier,” he says.

Although the problem is not new to the wine industry, Nel says not enough research has been conducted on the possible compounds and components that promote pinking, and reports describing curative treatments are few.

“Pinking was first noted in the 1960’s. However, in nearly 50 years there has only been several scientific peer-reviewed articles written on pinking, despite the fact that it is a worldwide phenomenon.”

Nel’s study, titled “Pinking of wine: Influence of different winemaking processes, causative agents and pinking treatment,” will explore the impact of the vinification processes on the wine’s potential to pink, including oxidative versus reductive must treatments, grape temperature, grape degree of ripeness, different press methods, skin contact period and wine on the lees.  The study will also explore whether pinking can be linked to a region in South Africa, a rootstock or yeast strain.

Nel says currently winemakers are making use of the substance polyvinylpolypyrrolidone (PVPP) to prevent pinking of white wines or to cure wines that have turned pink. There are up to 30 different products that are available to winemakers in South Africa, however, Nel says the effectiveness of these products have not yet been scientifically proven. 

Over the next few months Nel will test 30 of these products on wine with pinking potential.

“The products will be tested at three stages: at settling, during fermentation and on finished wine at the fining stage. The pinking potential of the wine will then be tested to determine which fining agent(s) work best with which treatment,” he says.

Nel’s study holds much promise for the multi-million rand South African wine industry and his findings will lead to the development of a protocol for winemakers.

*The study is being funded by WineTech.

Anton Nel can be contacted at This email address is being protected from spambots. You need JavaScript enabled to view it. of 073 424 0628.

Click here to read a recent article published in Wineland Media by Nel.

Written by Candes Keating
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Provides coverage for the Engineering and Applied Sciences Faculties; the Bellville and Wellington Campuses, and research and innovation news.

Determination has led lecturer in Enology and Crop Protection, Anton Nel to obtain his PhD in Agriculture at Stellenbosch University recently.

Nel’s research focus was about pinking on South African white wines. “This was a very difficult study as I needed grapes that will pink when the wine was made. Unfortunately, one cannot test for pinking of grape juice, so you have to take the chance. As a winemaker, you also have a small window period per year in which to do the winemaking and analysis. If you missed it, you have to wait another year to repeat. That made the whole study very stressful,” Nel recalls.

The father of two started with his undergraduate degree in 2004 at the age of 36 at Stellenbosch University. After obtaining his Bachelor of Science in Agriculture, Nel wanted to learn everything the university could teach him so he obtained his Master’s in Agriculture in 2010.

“After that, I thought that it’s time I give something back, so I started my PhD in 2014.”

Nel who started to work as a lecturer at CPUT in the same year, adds: “In the beginning it was easy. You do research, plan experiments, start a bit, but as time goes on, everything became exponentially difficult. While colleagues got classes or sabbaticals, my teaching load became heavier with no classes. In the end, I got a sabbatical, but I was more at work than at home.

But determination put me through.”

He explains that pinking is phenomena where white wines got a pink colour after some air contact. Nel reveals that nothing is known about what causes pinking and that he set out to investigate winemaking processes that will lead to pinking.

“That’s novel work as no one in the world ever did that. I also had a sensory analysis, which was also novel work as no literature exists on the sensory aspects of pink white wines. Getting wines to pink proved also to be difficult, so it costs a lot of time, travel, etc, to get what I want.”

Nel who is also a Health and Safety Representative for the Department of Agriculture in the Wellington campus is very proud of his achievements. “It’s something that I set out to do. As a small child, I always said I wanted to become a scientist. Now I am a wine scientist. This achievement came with very long and hard work and one is normally very tired after a full day’s work. Things that I enjoy, like reading or collecting kept me going as it was this that gave me the joy to go forward. My support of my wife and family also carried me through a difficult time,” he continues.

“My life was not easy. I never had a mentor to teach me the ways. I made a lot of mistakes in my life to come where I am now. I have learned a lot of things and I am using this knowledge to plough back to my students.”

His studies took away a lot of family time. He started when his son was four years old, he is now 21 years. “That means for 17 years of his life, I wasn’t really there. My daughter is now 10, so I don’t want to make the same mistakes I did with my son.”

When he is not working nor studying, Nel will be busy with another research topic. This one is about the extraction of wine phenols during white winemaking and the maturation of the skins for an extended period of time. “This research was also never being done here in South Africa. I belong to some associations of which I am sitting on the board of directors, so these things keep me going.”

Written by Aphiwe Boyce
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Winemaking is not a task for the fainthearted.

It requires patience, a sound scientific background as well as a love of wine, says second-year students following the Viticulture and Oenology stream in the Department of Agriculture.

To ensure that students have the knowledge and hands-on experience that will give them the edge in the wine industry, the class is currently producing their first wines, a several-week process that starts by crushing and destemming grapes and will culminate in the bottling process and final taste test.

Oenology lecturer, Anton Nel, says the task is part of the Oenology module designed to develop students' foundation in biochemistry and microbiology and ensure they gain an understanding of all the processes involved in the production of wine.

“In the first year, they are introduced to winemaking and we look at the history, biochemistry and microbiology. In the second year we focus on the practical part of winemaking. This involves the crushing of grapes, separation of skins and juice, balancing of the must, fermentation of juice and stabilization and filtering of the finished wine,” says Nel.

“In the third year, we look at the post-handling of the wine.”

Nel says this year he encouraged students to be creative and to put their skills to the test, tasking them to create a wine of their choice, and so far he is impressed with their efforts.

Student Amanda Gwiji opted to produce a merlot with a wooded taste, which required her to add blocks of French oak to the wine after the fermentation process.

“There are a lot of factors involved in the process of winemaking. You have to be very specific because you need to get a certain outcome.”

“Winemaking is an art that is science-based,” says Amanda.

Her classmate, Koos De Wet, is producing a wooded merlot and hopes that by introducing blocks of American oak during the fermentation process, the final product will by soft and full-bodied. He is also producing an unwooded chardonnay, with fresh, vibrant and fruity characteristics.

Koos welcomes the practical task and says it provides the class with an opportunity to put their theory into practice and gives them insight into what they can expect in industry.

Click here for more information on the National Diploma in Viticulture and Oenology.

Written by Candes Keating
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Provides coverage for the Engineering and Applied Sciences Faculties; the Bellville and Wellington Campuses, and research and innovation news.