How Important is Carbon Filtration and Polishing Your Spirit?

Reyka vodka is filtered through lava rock beds from Icelandic volcanoes.

A QUESTION I’m often asked is about the importance of carbon filtration in the distilling process, so I found an article which covers it pretty well.

Turbo Carbon – Specifically designed for use during fermentation. It actually adsorbs impurities as they are being formed by yeast in the wash, this is then dropped to the bottom with the yeast after the addition of turbo clear, vastly reducing the impurity level going into the boiler and increasing the efficiency of your filter carbon for a purer, cleaner and smoother spirit.

NOT ALL CARBON WORKS ON SPIRIT – there are only a few grades of carbon which are suitable for filtering spirit washes or finished spirit. Ie water filter carbon doesn’t do the job – “at all”. The size and number as well as the structure of the pores, Meso, Macro and Micro pores as well as the craggy structures around those pores will determine whether a carbon is effective in removing the impurities found in alcohol. ie you won’t get ANY improvement by filtering through the carbon used in water treatment or most of the other commonly available types. Use the right stuff.

There is something you can do at each stage to reduce the load on your carbon. Most commonly caused by poor quality yeast, inferior brewing sugars and failing to clear wash prior to distilling.

KNOWING THE LIMITS: There’s a limit to what carbon can do to improve spirit quality. ie Pushing the run too far (trying to collect too much) and too fast (keep in the 79°-81°C for best results). (thermometer placement on a still can affect how it measures while spirit is being collected. (It can vary from 76-82 for the “sweet spot” You should expect to yield 1 – 1.1 litre of spirit (after dilution to 40%), per kilo of fermentable used. Collecting much beyond 1.1 Litres of spirit (after dilution to 40%) will result in increasingly poorer quality alcohol and collection of a lot of other unwanted compounds – many of which won’t filter out through Carbon. More than this and you are ringing the neck of the beast and collecting additional unwanted fusels. Less and you are not yielding its full potential.

Summary: We suggest a maximum collection of about 1.1L per kg of fermentable sugars used in the wash. ie 6kg of dextrose in a 25L wash = discard first 100ml of foreshot, collect 2.8L of spirit @ 93% purity, broken down to 40% prior to filtration = 6.5L of finished filtered spirit @ 40% abv.

Always remember that late stage, unwanted fusels also test as alcohol, so don’t push your run too far.

IMPORTANT NOTE: Distilling at home isn’t entirely about finding the cheapest way possible to collect the largest quantity possible. For most, it’s about having pride in quality and thus quantity becomes a secondary consideration. Once you grasp the following few points, it’ll make a lot more sense:

A spirit wash, regardless of it’s composition, is only capable of producing around 1 to1.1litre of spirit at 40% for each kilogram of fermentable sugar whether it be Dextrose, Cane Sugar, Castor Sugar or anything else. Everything beyond that magic 1.1 Litre/kg mark detracts from the purity of what is collected. Now that that is established, if you collect say, for instance, 4 litres of spirit at 80% purity from a 6kg batch of ANY sugar, then you’ll effectively end up with 8 Litres which measures at 40%…..way beyond what is recommended. Just because a dumb float (Alcoholmeter) says it’s 40% Alcohol, doesn’t mean it’s 40% ethanol. Your batch will have quite a large amount of other poor quality alcohols making up the rest of that volume. Some of these aren’t exactly good for you over the long term.

A word on alcometers. Alcometers (alcoholmeters) are manufactured to exacting specifications and are designed to measure ethanol at a set temperature at sea level. Look at the side of your alcometer and it will have a temperature stamp on it. This is the only temperature that your meter will be accurate at. Other things also affect how it reads… altitude above sea level and even atmospheric pressure. We can’t cover everything here, but we can make the biggest adjustment to get the most accurate reading possible – when you’re trying to read the alcohol % get the spirit to the correct temperature by adjusting the measurement sample in either a fridge or by warming with your hands until it’s at the calibration temperature,ie. 20°C.

Dilute before filtering – Water down to 50% or less (40% is best) before carbon treatment. The reason for doing this is that unwanted flavour compounds are dissolved by high strength alcohol and are difficult for the carbon to remove over 50%. If you water down to 40% first, as a bonus, you also get your makeup water carbon filtered! And also save a later step to dilute to final 40% ABV.

Mineral Salts – Mineral salts are present in the raw materials used to make activated carbon. When spirit runs over activated carbon, mineral salts can beabsorbed into the spirit. Later these minerals start to become insoluble in the spirit and after a few days forms a fine haze which eventually drops to the bottom of the bottle as sediment. These mineral salts are 100% safe but you don’t want them in your spirit. This is why we recommend flushing the carbon with clean water (4-5 Litres of water per 100g of carbon) prior to adding to your spirit. If you notice this effect in your spirit you can decant it off after it settles.

As a rule, you will get better filtration through carbon which has been thoroughly wet with water first

Reusing Carbon – Don’t! Carbon can only be used once. A used batch of carbon contains all the junk you took out of the previous batch. Carbon works by micropore absorption, once these sites have been filled no more contaminates can be removed and pass straight through to your glass!

To reactivate carbon requires that you heat it to 500°C in an anoxic (oxygen added at this stage would cause an explosion) environment (such as an autoclave) and injecting with steam. Even if you could do this at home it is still cheaper to use a new batch!

Soaking / Polishing- Often used as a pre-treatment for filtering and, used this way, produces a very good result. Used if you have plenty of time on your hands – rather inefficient if not done properly, but can be effective, especially when used in conjunction with normal filtering.  .

The process of polishing your spirit is done by applying 10g of high activity carbon per litre of spirit in a vessel of suitable size. It’s then agitated several times a day for 2 days. It’s then agitated daily/twice daily for the next 2 weeks. The correct carbon to use for polishing is commonly known as “High Activity Carbon”. It’s an acid washed carbon in the activation process and should be first washed thoroughly, then soaked in clean water (1 litre per 100 g of carbon is sufficient) for 24 hours before use in spirits.

Double filtering? – A single pass through the filter should be enough to remove all odours and tastes from a batch of your spirit. If it is still present review your process and ingredients. 

Until next time… happy brewing!

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