© 2020 Laura Kline

Cleaning a copper still after distilling hydrolats is one of the most important steps in distilling. Having a clean still guarantees that the next distillation will not be adulterated or contaminated from previous distillations. Cleaning copper can be a little tricky but hopefully this article will help.

When distilling for hydrolat as the primary product, “the distiller must practice excellent hygiene. When the focus is on the essential oil, often little care is given to the cleanliness and sterilizing protocols that are crucial for a hydrosol distillation. Hydrosols are perishable, and can easily be contaminated by airborne fungal spores, bacteria and a lack of sanitation.” (Harman, 2015)

Cleaning Copper

I have seen people suggest cleaning methods from just rinsing out the still with water to the other end of the spectrum suggesting “…mineral spirits or other petroleum distillates.  Commercial carburetor spray cleaner excels…”(Rose, 2015) I also saw, within the spirit distilling forums, suggestions for cleaning copper. One consistent suggestion, in addition to the citric acid, is a bicarbonate of soda rinse. Bicarbonate of soda is commonly known as baking soda or bicarb. I wanted to discover how and if bicarbonate of soda can be used to clean our stills, what the benefit using it would be, and how to use it. I also wanted to see if we use citric acid correctly, with the correct dilution, at the proper temperature. This way we can clean and protect the copper, assuring that cross-contamination from previous distillations does not occur, and we distill each time with a fresh start.

Plus, taking it one step further, cleaning the copper to begin the process of passivation. The copper reacts to atmospheric oxygen, forming a brown copper oxide layer, protecting it from further corrosion. Passivation is when the copper reacts to atmospheric oxygen to form Cu(II). When passivation has happened it becomes the rich brown color that is also referred to as patina. This rich-brown color actually protects the metal and makes it stronger. Copper can also react with other elements in the atmosphere forming different layers and colors. The most recognized color is the pale green of the Statue of Liberty or as seen on buildings. This layer of patina is often called verdigris by many, but that is actually incorrect. Verdigris is when the green finish is man-made by a treatment with acetic acid. Verdigris is not as strong as the natural patina. (Copper Alliance, 2020)Just a note, the light green patina is actually toxic. The good news is that it takes over twenty years for it to develop and hopefully you use your still more often than once every twenty years. If your still, by chance, develops this patina clean it immediately.

Copper is a biostatic, antimicrobial metal and a necessary dietary mineral. It also will capture the “sulphur and yeast compounds that were not removed during the distillation process” (Harman, 2015)  making it perfect for distilling hydrolats. Copper also has it downfalls; it is prone to scale formation and can be easily damaged by etching and chelating, in acidic or base environments. Since hydrolats are acidic the still is constantly under attack.

pH

First of all, a little refresher on pH. pH is a measure of hydrogen ion [H+]concentration in an aqueous solution. The pH scale ranges from 0 to 14. A low pH value indicates acidity, a pH of 7 is neutral, and a high pH value indicates base or alkalinity. When used in cleaning products, acids, help break down difficult stains and mineral deposits making them easier to remove. Products with basic pH values are useful for removing organic soils, and breaking down oils and carbonized soil.

Multi-step Process

In order to properly clean copper stills, it is a multi-step process. The first is to remove any essential oil and hydrolat (alcohol), the second is to remove any organic material (bicarbonate of soda) and then because copper is prone to scaling, the removal and prevention is necessary (citric acid.) There is also just one more step, and that is sanitizing the still with steam. All the products are food safe, and if used correctly at the correct pH, they will cause minimal damage to the copper. In between each step, it is critical to flush the entire condenser system with warm water, rinsing the hat, pot, column (if used).

We also have to have equipment in order to clean: gloves, eye-protection, a condenser snake (rope with frayed ends or a piece of microfiber at the end), cotton cloths or microfiber, a non-scratch green pad can also be used. You have to be very careful when cleaning copper; never use brushes, steel-wool or abrasives which will scratch and gouge the copper. Use a cork or other stopper that will plug the outlet (parrots beak) in order to soak the coils. Due to the steam properties, it entirely coats the inside surfaces of pipes and all interior surfaces. Use cotton cloths or microfibers to dry when done cleaning, so water spots do not form on the copper. A properly calibrated pH meter with temperature is also necessary. Since pH is dependent on the temperature of the solution exact ratios will not be given.

First Cleaning

Rye flour is traditionally the first step in cleaning a new or rarely used still or at the end of distilling season within the hydrolat community. The origin of this step is unknown, although many manufacturers suggest it be done. Rye-flour distillations are probably the most dreaded part of cleaning a new still or putting one away at the end of season. It is extremely messy, and it seems to create more chaos than it should. Rye is an interesting grain, and when the flour is boiled, it is acidic. It also contains a type of non-starch polysaccharide named pentosan, which is partly soluble in water and partly insoluble, forming a gel in the body of the mixture of water and flour. The flour also swells when mixed with water. It is thought that the acidic nature  of rye-flour when boiled along with the grain pellets and the non-water-soluble gel of the pentosan helps remove any debris left over from manufacturing and anything left over from a season of distilling. Jill Mulvaney of Alembics, The Art of Distillation, has very good instructions on how to perform a rye-flour distillation. Her website is alembic.com.nz and in the How-To Guides you will see “How to look after your still.” The link is https://www.alembics.co.nz/how-to-guides/#look-after

Cleaning- First Step

After distilling, the first thing, after allowing your still to cool down, is to rinse it thoroughly with warm water. It would be best to use a cotton cloth or microfiber to dislodge any spent marc ^* as much as possible. A non-scratch green pad can be used. Also, thoroughly rinse the serpentine coils and gooseneck, using the snake.  Friction is necessary in cleaning to disturb the debris and disrupt any water film.

Clean with alcohol, an emulsifier, to remove the essential oil and hydrolat. Grain alcohol or isopropyl alcohol, at least 80 percent **can be used.  Stop up the end of the serpentine coil at the parrot beak and pour in the alcohol. The gooseneck should be either put into an alcohol bath or stopped so that you can put in alcohol and allow it to get on all sides of the pipe. Alcohol can be put into a spray bottle and then sprayed inside the pot, hat, and column. The alcohol can sit for a few minutes, then wipe or scrub the entire hat, pot, using a cloth and the snake on the gooseneck and coils. Flush with warm water.

*Marc is the spent botanical after extraction. It is a term borrowed from herbalism, used for centuries.
**In grain alcohols, the term proof is not the same as the percentage of alcohol in solution, e.g., 80 proof alcohol is 40 percent alcohol; a 180 proof is 90 percent alcohol.

Cleaning – Second Step

Bicarbonate of soda, bicarb, is a base (alkaline) in solution. It is highly soluble in water and at 50ºC begins to decompose to sodium carbonate, so for this step the temperature of the water must be below 50ºC.  For our purposes, we are using it to remove organic debris. Normally base solutions can corrode copper, but if the bicarb solution has a pH greater than 8.5, the copper dissolution is inhibited and actually passivates the copper surface. (Edwards,1994) This was due to catalysis of oxygen reduction (cathodic) reactions. In the article, Effect of Selected Anions on Copper Corrosion Rates, “the authors speculated that the change [from copper dissolution at pH lower than 8.5] results from a unique pH-bicarbonate effect on the identity and structure of scale forming on the surface…” (Edwards, 1994)

To use it, prepare the solution at a dilution to achieve a pH of 8.5 or greater. pH is temperature-dependent, but very little is needed. (It is approximately a 0.13wt% dilution at 48.3ºC.) Pour the solution into the stopped coils and allow to sit for up to 3 minutes, drain. Dipping your cleaning snake into the bicarb solution, clean out the coils, and flush. Use the bicarb solution, in another spray bottle, with up to a 3 minute hold on the rest of the pieces. Flush and rinse all pieces thoroughly.

Cleaning- Third Step

The next step is the citric acid. Citric acid is pretty well known and used on copper stills. Citric acid, is a weak acid and  the more concentrated the solution, the less it ionizes. So while the pH does decrease for more concentrated solutions, it drops more slowly as the concentration goes up. This implies a super-concentrated solution isn’t more effective at cleaning copper as a more dilute one.  We’ve been taught to “Test the strength of the acid by dribbling the hot citric acid on the outside of the still; if it immediately turns pinkish in color, then it is strong enough to clean the inside of the still.” (Harman, 2015)  I believe we have been using the citric acid in too strong of a solution based on its properties. Also, citric acid is citric acid. The strength does not need to be determined. It is a natural product usually derived from a fermentation process using sugar cane or yucca and a mold Aspergillus niger; the mold is filtered out and the citric acid is isolated and regenerated.

Citric acid works best in warm water, so prepare a solution to get a pH of approximately 2.0. (It is approximately a 0.5wt% dilution at 52.3ºC.) (Zhang, 2019) Repeat the same techniques as described above, holding the citric acid solution for up to 3 minutes before rinsing. If you like bright, shiny copper you can use this solution on the outside of your pot also, and then rinse thoroughly. Just remember that the copper will begin passivation to the rich-brown patina through a natural process.

Cleaning – Final Step

The next and final step is steam. Fill your pot half way or more with water and assemble the still. Distill for 10 minutes, without water in the cooling reservoir, so there is just a plume of steam from the parrots beak. Then turn on the cooling system and capture up to one-half of the amount of the water that you put into the pot. This steam-cleaning helps to sanitize your still and assure that it is rinsed well. Break down your still, when cool, and thoroughly dry, shaking out the serpentine coils and gooseneck. Steaming the still should be also done prior to any botanical distillation to sanitize the still after sitting unused. It will assure that you begin the next distillation with a clean still.

References

Baker, Chester L., Effect of Alkaline Detergents Upon Metals Aluminum, Copper, Tin and Zinc, Industrial Engineering Chemistry, 1935, 27, 11, 1358-1364.

Bayuseno, Athanasius, Jamari, Jamari, Muryanto, Stefanus, et. al., Calcium Carbonate Scale Formation in Copper Pipes on Laminar Flow, MATEC Web of Conferences 58, 01029 (2016) BISSTECH 2015.

Copper Development Association ltd.,, Copper Alliance, https://copperalliance.org.uk/knowledge-base/education/education-resources/copper-reactivity-patination/, retrieved 20 November 2020.

Edwards, Marc, May, Travis, Rehring, John, Effect of Selected Anions on Copper Corrosion Rates, Journal American Water Works Association, December 1994, Volume 86, Issue 12.

Goldhammer, Ted, The Brewer’s Handbook, Apex Publishers, 2008, Chapter 7 “Brewery Cleaning and Sanitation.

Gonzalez, S., Perez, M., Barrera, A. R., et. al., Mechanism of Copper Passivation in Aqueous Sodium Carbonate-Bicarbonate Solution Detrived from Combined X-ray, Photoelectron Spectroscopic and Electrochemical Data, The Journal of Physical Chemistry B., June 20, 1998.

Grass, Gregor, Rensing, Christopher, Solioz, Marc., Metallic Copper as an Antimicrobial Surface, Applied and Environmental Microbiology, 2011 March: 77(5): 1571-1547.

Harman, Ann, Harvest to Hydrosol, IAG Botanics LLC., 2015.

Heinio, R., Katina, K., Poutanen, K., et. al., Rye, Chapter 5, published in Bakery Products: Science and Technology, Hui, Y., et. al., Blackwell Publishing, 2007.

Rose, Jeanne, Distillation A How To Booklet, Herbal Studies Library, 2015.

Vargas, IT, Fischer, DA, Alsina, MA et. al., Copper Corrosion and Biocorrosion Events in Premise Plumbing, Material (Basel, Switzerland), 10(9), 1036.

Zhang, Wang, Lu, The Effect of Citric Acid Based Cleaning Solution on Particle Adhesion and Removal During Post-Cu CMP Cleaning, Microelectronic Engineering, V216, 15 August 2019, 111090.