Which yeast?

Karien O’Kennedy - 17 May 2018

The two most important considerations for an optimal fermentation are: The yeast must have the ability to ferment to dryness in the given conditions without becoming sluggish or stuck and within the time frame required for process optimisation; and the sensory profile of the yeast must complement and promote the varietal character of the grapes. These two aspects go hand in hand. However, the yeast’s fermentation capabilities are always more important than its aromatic profile.

How to handle high sugar musts

Karien O’Kennedy - 17 May 2018

Yeasts are living organisms and therefore have specific genetic capabilities and limitations. Here are a few guidelines on how to handle high sugar musts to increase one's chances of obtaining dry wines.

Spontaneous fermentation: How to handle the new-old kid on the block

Debra Rossouw - 17 May 2018

Interest in spontaneous fermentation is rising in wineries across the globe. This trend has various drivers, importantly consumer preference for a perceived ‘natural’ product, financial factors (no inoculation of pricey starter cultures) and quality considerations. For winemakers considering a first foray into spontaneous fermentation, here are some helpful hints to guide you on your journey.

Yeast nutrition during fermentation

Karien O'Kennedy - 17 May 2018

Yeast nutrition is added to fermentation primarily to ensure the completion of fermentation and to limit the formation of sulphur-like off odours. It is a fairly common practice seeing that grape juice often contain insufficient nitrogen. There are five types of yeast nutrition available on the market: basic yeast nutrition (mainly inorganic nitrogen – DAP), complex yeast nutrition (inactivated yeasts, inorganic nitrogen), rehydration nutrition (inactivated yeasts), organic yeast nutrients (inactivated yeasts) and yeast cell walls. Technically, yeast cell walls have no nutritional value but rather serve as detoxifying agents. The type and dosage of yeast nutrients needed depends various factors.

Management of grapevines during drought periods

IGWS - Lucinda Heyns - 21 Feb 2018

This document highlights a few practical guidelines for managing vineyards during drought conditions. Always bear in mind that these are merely guidelines and vineyard practices should be tailored to the specific area, climate, soil type and wine goal.

Image: Lucinda Heyns

Guava tree and cat's pee

Carien Coetzee - 02 Feb 2018

This manuscript focusses on volatile thiols in wine that are important compounds contributing to the varietal character of especially Sauvignon blanc wine. These sulphur containing compounds are one of the main reasons for the success observed in Marlborough Sauvignon blanc, with concentrations soaring to levels we can only dream of in South Africa. They are, however, not limited to one variety and significant contributions have been observed in other varietals such as Riesling, Colombard, Semillon, Cabernet Sauvignon and Merlot.  Research conducted at Stellenbosch University involves screening South African Chenin blanc wines to investigate the impact of volatile thiols on the characteristics of this varietal. So far, preliminary results look promising and could affect the way in which this variety is handled in the vineyard and cellar. However, to date, Sauvignon blanc has enjoyed the most attention when it comes to these potent molecules, due to the fact that large quantities can be found in wines made from this cultivar.

Could you clarify?

Jaime Gray and Malie McGregor - 02 Oct 2017

The clarification of white grape musts prior to alcoholic fermentation has long since been considered a necessary step in the production process of high quality white wines. With the unavoidable input of time, energy and/or money into the clarification process and the recent interest in trendy “dirty ferment” white wines, one is prompted to ask: why clarify at all?

A comparison between cold settling and flotation on white wine quality

Karien O'Kennedy - 04 Sep 2017

During the 2017 harvest season an experiment conducted at Groot Constantia by winemakers Boela Gerber and Rudolph Steenkamp, revealed that flotation does not harm white wine quality in any way. In fact, the wine from the tank that was clarified via flotation was incorporated into Groot Constantia’s premium Sauvignon blanc blend, whilst the settled tank’s content was assigned to the standard blend.

Guidelines to reduce smoke taint in grapes and wine

By: Karien O’Kennedy - 17 May 2016

Harvesting grapes from vines that have been exposed to bushfire smoke can result in wines containing smoke taint, commonly described as having “smoky, burnt and ash” aromas and “cigarette, ash tray, acrid and metallic” flavours. It is believed that smoke particles and associated aroma compounds enter the vine by absorbing onto the protective waxy cuticle layer or moving into the stomata on leaves and thereafter finding their way through the phloem into grapes.


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