WINETECH Technical Yearbook 2019

This study follows similar studies done by us on Chenin blanc, Chardonnay and Pinotage. The aim of this study was to determine the effect of seven different non- Saccharomyces yeast strains in combination with Saccharomyces cerevisiae and three malolactic fermentation strategies had on Shiraz flavour. INTRODUCTION Shiraz, also known as Syrah ( Vitis vinifera L.), is renowned for “spicy”, “dark fruit” and “berry”-like flavours and different wine styles can be produced, depending on the region of origin, as well as viticultural and winemaking practices (Mayr et al ., 2014). Non - Sa c c ha r omy c e s yea s t s po s s e s s different oenological properties to those of the standard wine yeast, Saccharomyces cerevisiae , and can be used to manipulate and improve the wine aroma and complexity (Jolly et al ., 2014). Most non- Saccharomyces yeasts are poor fermenters and are therefore used in combination with S. cerevisiae in co- inoculations, to complete the fermentation. Ma lol act i c fermentat i on (MLF) i s an enzymatic reaction performed by lactic acid bacteria (LAB) and is required for the production of some red wines, full-bodied white and sparkling wines. Malolactic fermentation increases microbiological stability of wine and can affect wine flavour through the modification or production of compounds, such as diacetyl, esters, higher

alcohols and volatile acids (Swiegers et al ., 2005). Various MLF strategies have been investigated with simultaneous (at the start of alcoholic fermentation) and sequential inoculation (after alcoholic fermentation) receiving the most attention (Bartowsky et al ., 2015). Selecting compatible yeast and LAB strains are essential for successful alcoholic and malolactic fermentation, as it has been shown that certain yeast strains negatively affect LAB growth and MLF (Alexandre et al ., 2004). W i t h t h e i n c r e a s e d u s e o f n o n - Saccharomyces yeasts, a need exists for a clearer understanding of the interactions that occur between S. cerevisiae , non- Saccharomyces yeasts and LAB. In a previous study (Du Plessis et al ., 2017), 37 non- Saccharomyces yeast strains were evaluated for use in wine production. The current study investigated the use of seven non- Saccharomyces strains, from five different species, in combination with S. cerevisiae and three MLF strategies. MATERIALS AND METHODS Each of the following seven non- Saccharomy- ces yeast strains, namely • Candida zemplinina (synonym Starmerella bacillaris ) (1),

MIXED CULTURE FERMENTATIONS AND SHIRAZ FLAVOUR

AUGUST 2019

HEINRICH DU PLESSIS 1,2 , MARET DU TOIT 2 , HÉLÈNE NIEUWOUDT 2 , MARIETA VAN DER RIJST 3 , MARTIN KIDD 2 & NEIL JOLLY 1 : 1 ARC Infruitec- Nietvoorbij, Stellenbosch, 2 Department of Viticulture and Oenology, Stellenbosch University, Stellenbosch, 3 ARC Biometry, Stellenbosch KEYWORDS: Yeast selection, lactic acid bacteria, malolactic fermentation, chemical profile, sensory evaluation.

• Lachancea thermotolerans (2), • Metschnikowia pulcherrima (1), • Hanseniaspora uvarum (1) and • Torulaspora delbrueckii (2),