Church window (wine)
Church windows (or tears / wine tears ) as a term of art in the tasting are spontaneously formed structures on the inner wall of a cognac - or wine glass .
Importance in wine tasting
The church windows provide information about the concentration of various ingredients. The viscosity of wine, for example, is influenced by its alcohol content - in particular by higher alcohols such as glycerine - and the sugar and extract content of the wine. The higher these values, the more viscous / viscous the wine, the slower and bigger the tears. Tears do not provide any direct information about the quality of a wine.
Alcohol-rich wines produce stronger tears and arched church windows, low-alcohol wines produce weaker tears and arched church windows.
Origin of the effect
Tears are created by swiveling the glass in a circle, causing the wine to wet its inner wall. After part of the liquid layer has evaporated, it does not flow further down, but upwards against gravity. The reason is that alcohol evaporates faster than water, which increases surface tension . The effect is greater at the top than at the bottom, not only because the layer is initially thinner there, but also because of the better ventilation there - especially pronounced with glasses that taper towards the top. Due to the higher surface tension, the surface “flows” upwards and pulls the thin layer with it ( Marangoni effect ). Since fresh liquid from the volume is drawn into the layer below, while alcohol continues to evaporate above, the Marangoni convection does not come to a standstill.
After a while, a ring of residual liquid collects on the upper edge of the wetted area, which is rich in sugar and other high-boiling components and becomes increasingly heavier. First of all, the surface tension, which also acts transversely, keeps the lower edge of the ring fairly smooth. The liquid will ultimately not run down flat, because where the lower edge of the ring happens to "hang" slightly, it absorbs more liquid from the layer more quickly than next to it, which causes differences in surface tension that promote the initial difference ( instability ). Eventually, the drops form. The rivulets that they leave behind remain clearly visible because the Marangoni convection now acting in the transverse direction feeds them further liquid and at the same time narrows them. The narrow, hanging threads are reminiscent of the skeletons of Gothic church windows.
The closer the drops get to the liquid level, the more violent the "head wind" of the Marangoni convection becomes. That is why they continue to grow before they empty at the meniscus . Sometimes the thread can then pull back a little and form another drop. According to studies by Andrea Bertozzi and colleagues, the drops are formed in the thin film of wine by under-compressive shock waves. In contrast to normal "classic" shock waves, these are unstable and do not meet the lax entropy conditions like these . With classic shock waves, the disturbances (in the sense of the characteristics method ) spread faster behind the front than at the front and more slowly in front of the front than at the front. This is not the case with under-compressible shock waves, a front forms in which the disturbances can spread more slowly behind the front than on the front.
See also
Individual evidence
- ↑ Church window link collection at http://de.mimi.hu
- ↑ Extract - Article in the wine dictionary on www.delinat.com
- ↑ Viscosity ( page no longer available , search in web archives ) Info: The link was automatically marked as defective. Please check the link according to the instructions and then remove this notice. - Article of the WorldWine Lexicon, editor Eckhard Supp.
- ↑ Alcohol-rich wines ( Memento from April 13, 2014 in the Internet Archive )
- ↑ Round arch, pointed arch ( Memento of the original from September 24, 2015 in the Internet Archive ) Info: The archive link was automatically inserted and not yet checked. Please check the original and archive link according to the instructions and then remove this notice.
- ↑ Glycerin content
- ↑ The first qualitative explanation of the Marangoni effect was made by James Thomson, Phil. Mag., Volume 10, 1855, p. 330
- ↑ Yonatan Dukler, Hangjie Ji, Claudia Falcon, Andrea L. Bertozzi, Theory for undercompressive shocks in tears of wine, Physical Review Fluids, Volume 5, 2020, 034002, Arxiv
