Technical

Suberic acid – a potentially flavor-active contaminant released by some agglomerated corks.
In: www.Infowine.com, Internet Journal of Viticulture and Enology, 2021, No. 9/2.
Liquid chromatography-mass spectrometry revealed that some agglomerated corks released more than 40 odorless compounds into the wine, which were not, or only in substantially lower amounts, released by natural corks. One of these compounds has been identified as suberic acid, a key component of the cork suberin polymer. This contamination generates sensory changes on the palate described as the tactile sensation of lingering astringency. Additional gustative changes have been confirmed by the use of an electronic tongue. In contrast to cork taint, they are identical in all bottles sealed with the agglomerated corks concerned since their production process delivers product homogeneity. Hence, they do not attract sensory attention when all bottles are sealed with the same cork, although they compromise efforts to create distinctive wines since the wines are uniformly affected by the bottle closure.
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Routine measurement of flavonoid phenols related to astringency and premature aging of white wines, and technical consequences
In: www.Infowine.com, Internet Journal of Viticulture and Enology, 2021, No. 6/3.
The use over many years of a fast and specific colorimetric method for the determination of flavonoid phenols in white wines and musts yielded far-reaching insights into the relationship between these phenols,  perceived astringency, and premature oxidative aging. Furthermore, it provided extensive data on the impact of various vinification techniques on their concentration. They are preserved under conditions of reductive must processing and lowered when must oxidation is allowed. The degree of must clarification plays an additional and decisive role in this process. Since, contrary to expectations, flavonoid phenols are already present in the pulp juice of the grapes, gentle grape processing alone is not sufficient to reduce them to a significant extent.
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Orange wines: Tannin extraction kinetics during maceration of white grapes
In: www.Infowine.com, Internet Journal of Viticulture and Enology, 2021, No. 7/3.
Color, astringency and related in-mouth sensations of orange wines, also known as amber wines, are mainly attributable to their tannin. It is extracted in considerable but highly variable amounts and qualities during the long maceration period of such wines. This study focusses upon the assessment of tannin extraction using simple total phenol measurements accessible to commercial winery settings. They show that comparable to red winemaking, fruit characteristics (cultivar, ripeness) as well as the duration and technical framework conditions of the maceration period determine the content of extracted tannins. However, a longer maceration time is required for its exhaustive extraction than for ed wine. Depending on the fruit, it can last from one to well over three months. The tannin levels obtained in this process approach those of light red wines and require appropriate measures for mauration during aging. For this purpose, orange wines cannot be compared with either standard white wines or with red wines.
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Influence of different screwcaps on white wine quality
In: Australian & New Zealand Grapegrower & Winemaker, 06/2021, 78-83.
Fruity white wines develop different sensory expressions of ageing. The best known of these is typical ageing, which is intensified by oxygen uptake via the bottle closure. Conversely, it is largely prevented by the widespread use of screwcaps, in some cases with hermetically sealing inserts. However, such closure systems promote the so-called reductive ageing through the formation of reductive taints  in the bottle. A functionalised liner for screwcaps opens up a way out of this dilemma.
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Wine screwcap closures: The next generation
In: Australian & New Zealand Grapegrower & Winemaker, 03/2017, 50-52.
Screw cap liners with a very low oxygen transmission rate (OTR) protect wines against oxidative ageing, but they also favour the occurrence of post-bottling reduction flavour. This article describes the concept of a new screw cap liner capable of mitigating the appearance of reductive taints. The innovative liner includes a layer containing immobilized copper binding volatile sulfur compounds present in the bottle headspace. Their scavenging by copper takes place within the liner. None of the copper leaches into the wine. The OTR of this liner is indistinguishable from that of a tin/Saran liner.
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Tannin and oxygen management in red wines
A detailed Powerpoint presentation from lectures and seminars.
with special consideration of cool climate conditions, tannin quality and quantity and how to measure it, sensory impact of micro- and macrooxygenation, tannin polymerization, sensory interactions between acidity and astringency, use and quality of oak, interactions between SO2 and oxygen, SO2 stability at bottling, etc.
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Primer on atypical aging
In: Wines and Vines, No. 4, 2010, 45-51.
Atypical aging is induced by a hormonal stress in the vines prompting the conversion of the plant hormon 3-indolacetic acid into the odor-active 2-aminoacetophenone after SO2 is added to white wines post fermentation. The typical off-flavor reminiscent of mothballs, acacia blossom, or laundry, can develop as a premature aroma defect that has no connection with oxygen uptake or oxidative degradation. However, the addition of ascorbic acid is the only useful enological means to prevent its appearance in wines made from affected fruit. Long-term solutions must be sought in the vineyard to avoid stressed fruit. The sensory identification and discrimation from other forms of aging is crucial in order to avoid inappropriate counter-measures.
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Aromatic and phenolic ripeness
Unpublished communication to the Pennsylvania Quality Association, 2010.
Sugar content of grapes is an unreliable parameter to predict grape and wine quality. Under conditions of progressing global climate change, extreme climates, overcropping, and premature harvest, the correlation between Brix readings and overall quality lacks any practical significance. Alternatively, the concept of physiological maturity, comprising aromatic and phenolic ripeness, is presented, Analytical and sensory means of their assessment  in grape samples are discussed.
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The pH-issue in winemaking
Unpublished communication to the Pennsylvania Quality Association, 2012.
High pH is a major concern in winemaking since it affects SO2 effectiveness and microbiological stability. However, lowering pH by acid additions generates drastic alterations on the palate that frequently distort the desired wine style. Filtration and sterile bottling are efficient means of risk management in high pH winemaking.
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The enological and sensory significance of acetaldehyde
In: Ithaka Journal for Terroir, Wine, and Biodiversity, 2009.
This paper reports on the microbiological production and breakdown of acetaldehyde (ethanal) in wine, its production and decay by chemical pathways, its interaction with sulfur dioxide, and sensory definitions and frequent misunderstandings related to it.
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