The reason for using a multi-bubble plates colume is to purify the alcohol like multi-time distillation. For detail, the below link will help you to understand the principles.(copy the link and paste into browser)
https://www.youtube.com/watch?v=M7AL7-44YTc
In general, it make less sense after 4 plates if you want it run as a pot still. However, we can supply extra still plate modular/bubble tee to add on yourself if you want a better setup.
The reason for using copper for the distillation colume mainly because
Copper absorbs sulfur-containing compounds and yeast cells which are produced during fermentation and the presence of which is undesirable in the distilled spirit or essential oil. Sulfur compounds and yeast cells
smell. Copper keeps the distillate sweet;
Copper reduces bacterial contamination;
Copper has excellent heat transfer properties, helpful for both heating and cooling of vapours;
Copper prevents the production of ethyl carbamate which is a toxic substance formed from cyanides (cyanides are found in the stones of fruits);
Copper also improves the quality of the final product. If the quality of the mash is not microbiologically perfect, copper will improve the aroma of the final product.
https://www.youtube.com/watch?v=NonKN3YAMHE