Fifty-one Canadian ice wines, representative of a range of varieties and vintages, were evaluated chemically and 20 wines further evaluated sensorally. Ice wines from British Columbia and Ontario were significantly different for a range of chemical and sensory attributes. British Columbia ice wines had higher titratable acidity, acetic acid and glucose, and lower colour and ethyl acetate content compared with those from Ontario. Apricot, raisin, honey and oak aromas were more pronounced in Ontario ice wines, while British Columbia ice wines had higher intensities of pineapple and oxidized aromas. Riesling ice wines had higher titratable acidity and glucose and lower pH and A 420 values compared with Vidal. Vintage effects were also found for pH, A 420 , glucose, fructose, ethanol and ethyl acetate.

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Aims: To determine acetic acid, acetaldehyde and glycerol production by wine yeast throughout Icewine fermentation. The expression of yeast cytosolic aldehyde dehydrogenases (ALD3 and ALD6) and glycerol-3-phosphate dehydrogenase (GPD1) were followed to relate metabolites in the wines to expression patterns of these genes. Methods and Results: Icewine juice (38AE8°Brix, 401 ± 7 g l )1 sugar), diluted Icewine juice (21AE3°Brix, 211 ± 7 g l )1 sugar) and the diluted juice with sugar levels equal to the original Icewine juice (35AE6°Brix, 402 ± 6 g l )1 sugar) were fermented in triplicate using the commercial wine yeast K1-V1116. Acetic acid production increased 7AE1-fold and glycerol production increased 1AE8-fold in the Icewine fermentation over that found in the diluted juice fermentation. ALD3 showed a 6AE2-fold induction and GPD1 showed a 2AE5-fold induction during Icewine vs the diluted fermentation. ALD3 was not glucose repressed when additional sugar was added to diluted juice, but was upregulated 7AE0-fold. Conclusions:The NAD + -dependant aldehyde dehydrogenase encoded by ALD3 appears to contribute to acetic acid production during Icewine fermentation. Expression of GPD1 was upregulated in high sugar fermentations and reflects the elevated levels of glycerol. Solutes in Icewine juice in addition to sugar contribute to the yeast metabolic response. Significance and Impact of the Study: This work represents the first descriptive analysis of the fermentation of Canadian Icewine, the expression patterns of yeast genes involved in metabolite production, and their impact on Icewine quality. A role for ALD3 in acetic acid production during Icewine fermentation was found.

2-Isopropyl-3-methoxypyrazine (IPMP) is a grape-derived component of wine flavor in some wine varieties as well as the causal compound of the off-flavor known as ladybug taint (LBT), which occurs when Harmonia axyridis beetles are incorporated with the grapes during juice and wine processing. The main objective of this study was to obtain robust estimates of the orthonasal (ON) and retronasal (RN) detection thresholds (DTs) for IPMP in wines of differing styles. The ASTM E679 ascending forced choice method of limits was used to determine DTs for 47 individuals in 3 different wines--Chardonnay, Gewürztraminer, and a red wine blend of Baco Noir and Marechel Foch. The group best estimate thresholds (BETs) obtained for IPMP (ng/L) were Chardonnay, ON: 0.32; Gewürztraminer, ON: 1.56, RN: 1.15, and red wine blend, ON: 1.03, RN: 2.29. A large variation in individual DTs was observed. Familiarity with LBT was inversely correlated with DTs for Gewürztraminer, and no difference in thresholds was observed between winemakers and nonwinemakers. We conclude that the human DT for IPMP is extremely low and influenced significantly by wine style and evaluation mode. We recommend against the reporting of single-threshold values for wine flavor compounds, and encourage the determination of consumer rejection thresholds for IPMP in wine.

To remain competitive in increasingly overcrowded markets, yeast strain development programmes are crucial for fermentation-based food and beverage industries. In a winemaking context, there are many yeast phenotypes that stand to be improved. For example, winemakers endeavouring to produce sweet dessert wines wrestle with fermentation challenges particular to fermenting high-sugar juices, which can lead to elevated volatile acidity levels and extended fermentation times. In the current study, we used natural yeast breeding techniques to generate Saccharomyces spp. interspecific hybrids as a non-genetically modified (GM) strategy to introduce targeted improvements in important, wine-relevant traits. The hybrids were generated by mating a robust wine strain of Saccharomyces cerevisiae with a wine isolate of Saccharomyces bayanus, a species previously reported to produce wines with low concentrations of acetic acid. Two hybrids generated from the cross showed robust fermentation properties in high-sugar grape juice and produced botrytised Riesling wines with much lower concentrations of acetic acid relative to the industrial wine yeast parent. The hybrids also displayed suitability for icewine production when bench-marked against an industry standard icewine yeast, by delivering icewines with lower levels of acetic acid. Additionally, the hybrid yeast produced wines with novel aroma and flavour profiles and established that choice of yeast strain impacts on wine colour. These new hybrid yeasts display the desired targeted fermentation phenotypes from both parents, robust fermentation in high-sugar juice and the production of wines with low volatile acidity, thus establishing their suitability for wine styles that are traditionally troubled by excessive volatile acidity levels.

Aims: We previously reported that the aldehyde dehydrogenase encoded by ALD3 but not ALD6 was responsible, in part, for the increased acetic acid found in Icewines based on the expression profile of these genes during fermentation. We have now completed the expression profile of the remaining yeast aldehyde dehydrogenase genes ALD2, ALD4 and ALD5 during these fermentations to determine their contribution to acetic acid production. The contribution of acetaldehyde stress as a signal to stimulate ALD expression during these fermentations was investigated for all ALD genes. The expression of glycerol-3-phosphate encoded by GPD2 was also followed during these fermentations to determine its role in addition to the role we already identified for GPD1 in the elevated glycerol produced during Icewine fermentation. Methods and Results: Icewine juice (38AE5°Brix, 398 ± 5 g l )1 sugar), dilutedIcewine juice (20AE8°Brix, 196 ± 4 g l )1 sugar) and the diluted juice with sugar levels equal to the original Icewine juice (36AE6°Brix, 395 ± 6 g l )1 sugar) were fermented in duplicate using the commercial wine yeast K1-V1116. Acetic acid and glycerol production increased 8AE4-and 2AE7-fold in the Icewine vs the diluted juice fermentation, respectively, accompanied by a fourfold transient increase in acetaldehyde in the Icewine condition during the first week. Both mitochondrial aldehyde dehydrogenases encoded by ALD4 and ALD5 were expressed, with ALD5 expression highest at the start of all fermentations and ALD4 expression increasing during the first week of each condition. ALD2, ALD4, ALD5 and GPD2 showed no differential expression between the three fermentation conditions indicating their lack of involvement in elevating acetic acid and glycerol in Icewine. When yeast fermenting the diluted fermentation was exposed to exogenous acetaldehyde, the transient spike in acetaldehyde increased the expression of ALD3 but this response alone was not sufficient to cause an increase in acetic acid. Expression of the other aldehyde dehydrogenases was unaffected by the acetaldehyde addition. Conclusions: The aldehyde dehydrogenases encoded by ALD2, ALD4 and ALD5 do not contribute to the elevated acetic acid production during Icewine fermentation. Expression of GPD2 was not upregulated in high sugar fermentations and does not reflect the elevated levels of glycerol found in these wines. Acetaldehyde at a concentration produced during Icewine fermentation stimulates the expression of ALD3, but has no impact on the expression of ALD2, -4, -5 and -6. Upregulation of ALD3 alone in the dilute fermentation is not sufficient to increase acetic acid in wine and requires additional responses found in cells under hyperosmotic stress.

The introduced biological control agent Harmonia axyridis (Pallas) (Coleoptera: Coccinellidae) has attained pest status in North America as its presence in vineyards during harvest may compromise the quality of the resulting wine. Control of H. axyridis in vineyards is difficult as their populations may fluctuate daily, and there are few products registered to control this pest. Sulfur dioxide, in the form of potassium metabisulfite (KMS), is commonly used in wine as both an antimicrobial and an antioxidant. In this study, the effectiveness of KMS as a repellent against H. axyridis was measured. In a Y-tube olfactometer, H. axyridis spent significantly less time in the treatment arm (KMS 2.5, 5, and 10 g/liter) than in the control arm during a 10-min period. When sprayed in a vineyard, KMS significantly reduced the number of H. axyridis on grape vines. KMS is an effective repellent against H. axyridis and may be suitable for use in vineyards to control this pest. KMS (5 g/liter) applied to Riesling grapes at 2 wk, 1 wk, 3 d, or 1 d before harvest did not affect free sulfur dioxide in either freshly processed or settled juice. This study lays the foundation for the development of a pest management strategy incorporating repellents for H. axyridis in vineyards.

Background and Aims:  3‐Isopropyl‐2‐methoxypyrazine (IPMP) is both a grape‐ and insect‐derived trace compound found in wine that can contribute green characters. There has been renewed interest in examining how wine IPMP concentrations can be modulated due to recent concerns regarding ladybug taint – an off‐flavour from IPMP extracted from Harmonia axyridis (Pallas) (multicoloured Asian lady beetle). This study sought to determine the influence of commercial Saccharomyces yeast strains on IPMP concentration in Cabernet Sauvignon wines and to describe their sensory impact. Methods and Results:  Rehydrated juice from Cabernet Sauvignon concentrate was spiked with 30 ng/L IPMP and fermented in triplicate by yeast strains Lalvin BM45, Lalvin EC1118, Lalvin ICV‐D21 or Lalvin ICV‐D80. IPMP concentration was determined using headspace solid‐phase micro‐extraction coupled with gas chromatography mass spectrometry (HS‐SPME‐GC‐MS), and was unchanged from juice levels in wine fermented by EC1118, Lalvin D21 and Lalvin D80 but increased by 11 ng/L (29%) in wine fermented by Lalvin BM45. Yeast strains differed in their sensory impact on wine made from IPMP‐spiked juice for five aroma and four flavour attributes. Conclusions:  HS‐SPME‐GC‐MS allows for sensitive measurement of IPMP that, for the first time, has demonstrated the capacity for wine yeast to affect IPMP concentration. Yeast strains demonstrate varying ability to mask green or ladybug taint characters in wine. Significance of the Study:  This information should be useful in guiding selection of yeast strains for juices of high IPMP concentration, including those that are multicoloured Asian lady beetle‐affected, under‐ripe or from varieties with high methoxypyrazine loads such as Cabernet Sauvignon.