Which Packing to Choose? Steel Scrubbers or Spiral Prismatic Packing (SPP)? Stainless Steel or Copper?
The best combination is a copper reflux still with stainless packing. But why is that? The height and type of packing play the most significant role in the quality of the final product. The separation efficiency of a reflux still depends on the number of so-called "theoretical plates." Where does this term come from?
Large industrial rectification stills work on the principle of multiple condensations and evaporations of vapors from these plates. The home equivalent of this system is a plate still that doesn’t contain packing but instead has physical plates. Reflux stills for alcohol, designed to fit within “home-friendly” heights, use packing instead of plates. This can include scrubbers, SPP, or even inefficient "inventions" like crushed glass or metal shavings. The idea is that the packing provides a surface where the condensate can repeatedly evaporate and condense, mimicking the function of a plate and earning the name "theoretical plate."
Now to the key point: the height of a given type of packing corresponds to a real plate—this parameter is called HETP (Height Equivalent to a Theoretical Plate). Because packing is "three-dimensional," unlike a flat plate, a given volume contains more surface area, enabling more condensation and evaporation. Imagine a flat A4 sheet of paper: it covers 62 cm² on your desk. But if you crumple it, the same surface fits into a 4 cm² space, just taking up more height. Packing in a still works the same way—the more surface area per unit volume, the better the process.
For example, with steel scrubbers, the plate height is around 4 cm, while with stainless steel SPP, it's 2 cm. This means every 2 cm of still height corresponds to one “plate,” or one distillation cycle. However, the HETP parameter changes during the process (a phenomenon called "plate stretching"), which is why you can’t replicate a plate still with a reflux column still, where the number of plates is fixed.
The more plates in a still, the greater its separation efficiency. By comparison, crushed glass has a plate height of about 13 cm. In 100 cm of steel scrubber packing, there are around 25 theoretical plates, while with SPP, there are 50, and with crushed glass, just over 7.5.
Should the Packing Be Made of Stainless Steel or Copper?
Paradoxically, the answer is stainless steel.
Why? Stainless steel SPP has more surface area than the simple surface area of the wire from which it is made. Between the coils, small triangles form, where a film of condensate appears during the process (similar to the effect seen when blowing soap bubbles). This means the actual surface area is larger than the material used to produce the packing.
Unfortunately, copper springs, due to the nature of copper being less springy than the same-diameter steel wire, form a different shape during production. This prevents the formation of those "pockets" for condensate, and the springs themselves have a much worse surface-to-volume (S/V) ratio.
While the HETP for stainless steel SPP ranges between 2-3 cm, for copper SPP, it’s about 12 cm. The more plates, the purer the distillate, so using copper SPP worsens the quality of the product!
What About Scrubbers?
Stainless steel scrubbers are made by rolling stainless steel wire into "ribbons," which are then tightly coiled into balls that also work excellently as still packing. However, be cautious about so-called "copper scrubbers"—they don’t exist. Copper is too soft; when rolled this way, it crumbles and breaks. Scrubbers sold as "copper" are made of black steel with a thin layer of copper electroplated onto them. Unfortunately, this layer wears off quickly—after two or three processes, it’s gone, and the scrubber (now black steel) will rust. Even worse, some products being sold as “scrubbers” are actually brass soldering pads, which contain lead. There’s no reason to consider using copper packing in your still—it will only degrade the quality of your product!
What About the Smell?
Stainless steel stills usually produce distillates with much worse smell and taste. For this reason, a catalytic filter (a section of packing made of copper springs) is necessary to mask the “eggy” smell caused by sulfur compounds in stainless steel stills. This is why owners of steel equipment—significantly inferior to copper stills—have to resort to using poor-quality packing.
In a copper still, however, the internal surface of the still itself is enough to provide the necessary catalytic properties and reduce unwanted fractions. This means the entire useful volume of the still can be filled with high-performance packing that provides the separation efficiency required to produce an odorless 96%+ product. This is why the best choice for packing a copper reflux still is stainless steel spiral prismatic packing (SPP). In this setup, there’s no need to maintain a catalytic filter every process—no need to empty it, etch it, neutralize it, dry it, and refill it. A copper still with stainless steel packing is almost maintenance-free!
If you want to upgrade your still’s packing from scrubbers to SPP, you can purchase it HERE. If you need copper SPP, it is available HERE.
Clicking the link will take you to Henitom packing (best known in the community as "Polish SPP"), specially selected for optimal performance in your still. The required amount is described in the product description for each type of still and simple distiller.