When botanicals, including onion, are soaked in neutral spirits and then redistilled, a unique and stimulating aroma is obtained.
After distillation, when I opened the still, I found a thin metal membrane. This was something I had never seen before. What typically happens when distilling onions, and what perhaps was a rare occurrence this time?
First, let’s look at the characteristics of distilled onions.
The characteristic aroma and spiciness of onion is formed by volatile organic compounds containing sulfur.
It is rich in volatile sulfur compounds (allyl sulfides, thiosulfinates, etc.), and the warm and spicy aroma unique to the Allium genus is extracted by distillation. Based on this, unexpectedly sweet and umami notes can appear, which can create originality in craft spirits and flavor development.
As a flavor extracting component, it can also be expected to play a secret role in recipes that require flavoring, umami, and dashi-like nuances for pickled raw alcohol.
Ingredients in onions
Allicin
It is not contained in onion itself, but is produced enzymatically when the tissue is destroyed.
Thiosulfinates
The cause of tears when cutting onions.
Highly volatile, it becomes the main flavor during distillation.
Allyl sulfides
Easily produced by distillation and heating.
They are the basis of the “fried aroma” and “umami aroma” that are unique to onions.
These aromas give the distillate a pleasant nuance.
Onions are distilled in a copper pot still.
Here, we would like to draw your attention to the effectiveness of using a copper pot still.
Copper reacts with these sulfur compounds to form copper sulfide.
This reaction is often desirable, for the following reasons:
- It reduces the excessive sulfur and “onion” odors (suppresses off-flavors)
- It produces a cleaner, smoother distillate
Effects on copper stills
Repeated distillation can cause a dark copper sulfide coating to form on the inner walls of the copper, reducing its reactivity.
For this reason, it is recommended to regularly clean and acid-wash the still (especially after using sulfur-rich materials such as onions).
Metallic thin film
Here, something unexpected happened, so we will describe it here.
When I opened the door of the still, a thin silver film had formed on the opening and closing part. I was surprised by the presence of a thin metal film.
I think this was probably caused by the metal used in the door reacting with sulfur compounds.
If there are silver-plated parts, silver wire, or other metals (zinc, aluminum) inside a copper still, they may react with sulfur compounds to produce silver-based or platinum group metal crystals. Silver (Ag) reacts very easily with sulfur, and although silver sulfide (Ag₂S) is black, it has been reported that it can take on a silvery glossy structure during the growth process.
This metal film could be removed by gently wiping it off.
In addition, the blackening of copper sulfide, which was a concern, could be cleaned off by cleaning the still while it was still warm. Not only that, but the black copper sulfide film that had formed up until then could also be washed away.
Using botanicals that contain a lot of sulfur compounds, such as onions, was an interesting task that allowed me to rediscover the properties of copper pot stills that I had not noticed before.
コメント