The effect of copper on stills
In the distillation process, it is not difficult to find that the copper still has the functional advantage of removing the odor and optimizing the aroma compared with the stainless steel still. When fruit wine distills brandy, the aroma of spirits distilled by copper stills is more natural and pure, and the fruit aroma is delicate and elegant; when whisky is distilled from grains, the aromas of spirits distilled by copper stills are also more pure and harmonious than those of stainless steel stills. Material distilled spirits often have a meat-like aroma. For the original wine containing a small amount of sulfur, the spirits distilled from stainless steel stills have a sulfur smell, and copper stills can be used to reduce the sulfur smell. This phenomenon also reflects that copper stills have a certain role in removing sulfur smells.
Common off-flavors originate from sulfides. Among the various sulfides, trisulfides (DMTS) have been studied to have a dominant effect, with a sensory threshold of about 0.1 μg/L, or the concentration in new wine. About 1 to 6 micrograms / liter. According to research, when using copper and stainless steel stills, only DMTS produced significant differences in various sulfides, as shown in the figure:
However, not all copper has the same effect. For example, in the experiment of glass stills, adding copper salt (cuprous chloride) will increase the content of DMTS, while adding copper mesh will reduce the effect of used copper stills. It's better than new, and even other metal ions in the juice will have an impact. The catalytic action of copper converts thiols to less pungent carbonyls.
Some foreign teams have conducted experiments on the influence of copper in different parts of the still on the style of distilled wine. Taking whisky stills as an example, the wine juice and spirits stills are disassembled into 6 parts, respectively replaced with stainless steel. The still can remove the unpleasant sulfur, meat and other unpleasant smells and make it look cleaner.
Remarks: The author has also used stainless steel stills and copper stills to distill and distilled whisky. Through the comparison of smell, it can be clearly found that the aroma of distilled wine after distillation with copper stills is more fresh and natural, while the distilled wine with stainless steel stills has obvious similarities. The aroma of raw pork.
(Interested friends can download the English literature at the end of the article or refer to the chapters in the distillation section of "Whisky Science")
"The role of the condenser in spirit stills is quite subtle, and replacing a copper condenser in an all-stainless steel still will hardly help, but replacing a stainless steel condenser in an all-copper still will greatly increase the off-flavor. In the final stages of distillation, the presence of copper has a decisive effect, more likely because high-alcohol spirits are more likely to react with copper."
——Source: "Whisky Science", the arguments of this part of the book also mainly refer to the following documents:
Effects of copper in different parts of malt whisky stills on composition and aroma of new wines
(The Impact of Copper in Different Parts of Malt Whisky Pot Stills on New Make Spirit Composition and Aroma – Barry Harrison, Olivier Fagnen, Frances Jack and James Brosnan)
The concluding part of the paper is also translated as follows:
"The presence of copper in pot stills is important for controlling sulfurous and meaty aromas in new wines, and DMTS levels show a good correlation with these aromas. In these lab-scale distillations, it was found that placing copper in wine Condensers of juice stills or stills of spirit stills can best reduce levels of this compound. To improve control of this compound, it needs to be clarified that these areas of the still are more effective at reducing DMTS than other areas. valid reasons.
The performance of copper in the condenser of spirit stills in controlling sulphur and meat aromas also plays a role, but the mechanism of this effect is unclear. These results suggest that copper removal from these fractions may have the most significant effect on the aroma of freshly made spirits in industrial-scale stills. Furthermore, it was pointed out that while DMTS made a significant contribution to sulfur and meat aroma, other unknown compounds also made important contributions, and future research efforts should focus on identifying such compounds. "
In the production of Scotch malt whisky and French cognac, the use of copper to make stills for distillation is believed to play an important role in the aroma of distilled spirits. This experiment shows that copper is more effective in some parts of the pot still than others. This information can be used to assist in still design and maintenance, such as the style characteristics of the still spirit, the level of copper loss in the still, etc.
Nowadays, many domestic wineries have begun to experiment with the type and material of the distiller. For example, well-known domestic liquor factories will use traditional brandy Charente stills for distillation; some people add copper purification balls, goosenecks and condensers to the design of traditional liquor stills; The copper still for whisky or brandy will be replaced with stainless steel, and a detachable copper plate will be prepared for the still.
