WINETECH Technical Yearbook 2020

with H. uvarum in combination with VIN 13 and L. plantarum as a sequential MLF inoculation scored the highest for fresh vegetative aroma. Wines produced with H. uvarum in combination with VIN 13 consistently produced wines with high fresh vegetative aroma scores and this trend was observed for non-MLF and MLF wines. These results indicate that the H. uvarum and VIN 13 combination can be used to enhance the fresh vegetative character in wines where this attribute is lacking, or to produce a wine style with a predominant fresh vegetative flavour profile. On the other hand, if a wine with less fresh vegetative character is preferred, the use of a yeast strain such as NT 202 is recommended. Overall, sequential MLF wines scored higher for spicy aroma than simultaneous MLF and non-MLF wines. Of all the various treatments, sequential MLF wines produced with VIN 13 in combination with H. uvarum and L. plantarum scored the highest for spicy aroma. Differences in spicy aroma scores were found for wines produced with the two LAB strains and were affected by yeast combination, as well as the MLF strategy. Therefore, to increase the spicy flavour in wine, MLF should be induced as a sequential inoculation. Wines produced with VIN 13 scored slightly higher for body/mouthfeel than those inoculated with NT 202. Wines

wines produced with S. cerevisiae only, but were below 0.6 g/L. Wines inoculated with VIN 13 took longer to complete MLF than wines produced with NT 202 or H. uvarum in combination with VIN 13 or NT 202. Co-inoculated MLF completed in a shorter period than sequential MLF. Wines inoculated with O. oeni completed MLF in a shorter period than those inoculated with L. plantarum and this trend was observed for both co-inoculated and sequential MLF. We recommend that for fast and successful completion of MLF, a MLF- compatible yeast combination should be used with a commercial O. oeni strain as a co-inoculation. Our results show that yeast selection, LAB combination and MLF strategy had a significant impact on the volatile compounds and sensory profile of the wines. Yeast treatment had a significant effect on fresh vegetative (herbaceous, grass, bell pepper, mint and tomato leaf) and spicy (cloves, pepper, aniseed, cinnamon, liquorice and nutmeg) aromas, as well as the body and astringency of the wines. Wines produced with the selected LAB strains and MLF strategies were significantly different in terms of berry, fruity, sweet associated and spicy aromas, as well as acidity and body. Sequential MLF wines scored higher for fresh vegetative aroma than simultaneous MLF and non-MLF wines. Wines produced

bacteria (LAB) and is required for the production of some red wines, full-bodied white and sparkling wines (Bartowsky et al ., 2015). Malolactic fermentation is mainly used to ensure microbiological stability and modify wine flavour. The two main MLF inoculation strategies are co-inoculation (at the start of alcoholic fermentation) and sequential inoculation (after alcoholic fermentation). Selecting compatible yeast and LAB strains are essential for successful alcoholic and MLF, as it has been shown that certain yeast strains negatively affect LAB growth and MLF (Alexandre et al ., 2004). With the increased use of non- Saccharo- myces yeasts in wine production, a need exists for a clearer understanding of the in- teractions that occur between S. cerevisiae , non- Saccharomyces yeasts and LAB. This study investigated the interactions between H. uvarum , two commercial S. cerevisiae strains, two LAB species ( Lactobacillus plantarum and Oenococcus oeni ) and three MLF strategies, as well as how these inter- actions affected Shiraz wine composition and flavour. MATERIALS AND METHODS Commercial S. cerevisiae cultures were used for Shiraz wine production. The H. uvarum strain was obtained from the ARC Infruitec-Nietvoorbij microorganism culture collection. Four different yeast

treatments were used: S. cerevisiae VIN 13, S. cerevisiae NT 202, H. uvarum in combination with VIN 13, and H. uvarum in combination with NT 202. Each yeast treatment was also used in combination with O. oeni (Viniflora ® oenos), or with L. plantarum (Enoferm V22). Additionally, two MLF strategies were applied: • Co-inoculation of LAB (hereafter referred to as co-inoculated MLF) and • sequential inoculation of LAB (hereafter referred to as sequential MLF). For co-inoculation, LAB were inoculated 24 hours after yeast and for sequential inoculation, LAB were added after alcoholic fermentation. In total, 20 treatments were evaluated in triplicate. Commercial cultures of either O. oeni or L. plantarum , were used to induce MLF. A standardised small-scale (20 L) winemaking protocol was followed at an ambient temperature of 24°C. After completion of MLF, wines were bottled and stored at 15°C. The volatile chemical composition of the wines was analysed and descriptive sensory evaluations of the wines were also done. RESULTS AND DISCUSSION Al l the Shiraz wines fermented to dryness (residual sugar <4 g/L) after five days. Wines produced with H. uvarum in combination with S. cerevisiae had slightly higher volatile acidity levels than

WINETECH TECHNICAL YEARBOOK 2020 97