The bitter taste of sunburned grapes

‘Bakkie Tan’ or ‘Bakkie Arm’ is a thing. This term is used to refer to the right arm of a driver, usually of a bakkie, that turns a sexy shade darker due to repeated sun exposure. Well, the sexy part is debatable, given the uneven nature of the tan. Anyway, grapes can also get a tan, but if it goes too far both the grapes and the winemaker gets burnt. Which for some might be a painful experience similar to listening to a song called ‘Bakkie Arm’. Or for some pleasant. I don’t judge.

We are more alike than you think

Grapes and humans are not that different after all. Just like us, our juicy friends consist mostly of water, like to hang around and socialise in bunches, get sick, and can get sunburn. The human body’s response to sunlight is that the skin produces more melanin, which protects the skin from ultraviolet rays. This darkening of the skin gives you that lovely Bakkie Tan. Grapes, on the other hand, produce polyphenols, carotenoids and various aromatic compounds as a shield against sunburn. Unfortunately, this means the winemaker must deal with elevated levels of polyphenols in his juice.

But it’s not only elevated phenolics the winemaker must worry about in the case of sunburned grapes. Green tannins, whacky acid levels, low juice yield, and high protein content are also associated with heatwaves and sunburn. Ostensibly, elevated phenolics remain the biggest quality threat in a sunburn scenario. And hence the focus thereon in this blog.

Polyphenols – potential party poopers

The early fining of juice and wine remains key in addressing undesirable phenolics. Unless you like the increased odds of bitterness and oxidation (browning and off flavour) in your finished wine. I certainly don’t. You see, fining agents are typically less effective in wine than in juice and higher doses are needed. So, there is a quality and cost benefit to early fining.

Enter the fining agents

In white juice (both for settling and flotation) we recommend POLYMUST® PRESS. This product serves your juice with a triple whammy of vegetal protein (potato/patatin), bentonite and PVPP. This harvest there has been an increased incidence of juice that is harder to settle than usual, which can be a symptom of elevated protein levels in juice – I mentioned this earlier. The bentonite component in POLYMUST® PRESS will address the proteins and allow for lower levels of bentonite usage post-AF. Another fining product to consider is POLYMUST® BLANC, which is a combination of vegetal protein (pea) and PVPP.

In red fermenting must we recommend VEGEFINE®, a blend of patatin proteins, which will not only fine polyphenols, but also compact solids and lees. The best time of application would be right after the cap has formed. More options are VEGECOLL® (patatin), which can be added right after cap formation and POLYMUST® PRESS, for the early fining of press fractions.   

In addition to POLYMUST® PRESS, increased protein levels during heatwaves and sunburn in red must can also be addressed with TANIN VR SUPRA® added at the crusher. In my previous blog, I wrote quite a bit on oenological tannins. Click here to go to that blog, and here for a protocol for dealing with grapes harvested in a heatwave.

And now the bit that all of you’ve been waiting for … Click on this link to listen to ‘Bakkie Arm’. Full volume. You’re welcome.

Cheers!