Originally By Tony Ackland
Stripping the Wash (First run)Pot stills can be used to "strip" the wash, prior to a reflux distillation. By passing the wash once through a pot still, it will be increased in purity from say 10-15% up to 40-60%, reducing it in volume by 4/5th. This way, you can strip say 100L of wash down to 20L of semi-clean spirit to then load into the reflux still for a single pass (rather than having to do 5 reflux passes of 20L of wash). This will not only save you plenty of time, but it will also help result in a somewhat cleaner spirit, as any yeast, etc get removed during the stripping run. You could also use a reflux still to do the stripping in, by simply not making it reflux any of the liquid.
When you do your stripping run, it can be beneficial to add some sodium bicarbonate (baking soda) to the first-run alcohol, prior to the second ru n. As explained up in adding salt this will help clean up the taste greatly.
Mike explains the chemistry ...
Taking the last first, if an aqueous solution of sodium bicarbonate (baking soda) is warmed then it starts to decompose with the formation of sodium carbonate, water and carbon dioxide, the decomposition being complete on boiling. Good grief . that's why Granny uses it for her soda bread. The carbon dioxide leavens it! The reaction is: 2Na.HCO3 = Na2.CO3 + H2.CO3 [and H2CO3 -> CO2 + H20] [water + sodium bicarbonate = sodium carbonate + carbonic acid + lye] and the carbonic acid further disassociates to form carbon dioxide and water, particularly when heated [H2.CO3 = CO2 + H20]. Add tartaric acid and you have a quicker reaction with more CO2, and you then call the stuff baking powder which Granny uses to make her nice light scones.
Working back a bit, where did all that ethyl acetate come from? Well, we all know about vinegar (acetic acid, a fatty acid), and that a 'dirty' ferment or a bruiser of a fast yeast can result in quite a bit of that. What may not be generally known is that fatty acids react with alcohols to form esters, and acetic acid and ethanol get together to form ethyl acetate which is . you've guessed it . an ester with the composition C2H5.COOH
So now we add baking soda (sodium bicarbonate) to try turn all that that ethyl acetate, which started out as vinegar, into booze. Why bicarb? Well, although it's an acid salt of carbonic acid, it turns out that in an aqueous solution it's alkaline, due to hydrolysis. The Na.HCO3 disassociates to form Na+ and HCO3- ions, and the H+ ions from the water (H.OH) combine with the HCO3- ions to form undisassociated carbonic acid H2CO3. This leaves heaps of Na+ and OH- (hydroxyl) ions mooching around . and those two together spell sodium hydroxide . a strong base. So what happens when these ions bump into ethyl acetate? The sodium ion grabs hold of the COOH bit to form NA.COOH, sodium acetate, and the hydroxyl ion grabs the C2H5 bit to form good old C2H5.OH, booze!
But hang around a bit! What happens to all that sodium carbonate [NaCO3] that was left behind when the baking soda disassociated? Well, it's quite handy because it too disassociates in an aqueous solution to form more carbonic acid and lye, with an excess of hydroxyl ions floating around [Na.CO3 + 2H.OH = H2CO3 + Na.OH + 2OH-]. Now this deals to any excess acidity you might have, the OH- ions grabbing acid H+ ions to form water. Not only do you get more Na.OH for conversion of acetate to booze, but the solution is buffered to a pH of just over neutral 7.
This gives us the clue that oyster shells or chalk [CaCO3] will do the same thing, and will also work to convert ethyl acetate to booze as the stuff disassociates in the same way [Ca.CO3 + 2.H.OH = H2CO3 +Ca.OH + 2OH-]. In this case it's the Ca+ ion that grabs the COOH bit of the ethyl acetate to form calcium acetate [Ca.COOH] and the hydroxyl ion grabs the C2H5 bit to form what we're after . C2H5.OH, booze. The only thing to consider is the relative solubility of baking soda compared to chalk, but those who use hard water to dilute their strippate may be on a winner!
Now those who haven't fallen asleep already will be wondering why they can't just add a good dose of lye (Na.OH) to the brew and be done with it. Snag is, how do you know when enough is enough? Put too much in and you have a surplus of lye in the brew, and nothing to counter that. Keeps the boiler clean, but corrodes the hell out of it. In contrast, by using baking soda or oyster shells/chalk you end up with sodium/calcium acetate, and that is also a pretty good buffer, like the sodium/calcium carbonates.
Much too has been made about how long this treatment takes. What has to be borne in mind is that it is a relatively slow reaction compared with inorganic reactions that go at the speed of zip. So all it comes down to is how impatient you are. Some might argue that heating the solution up will speed the reaction as it will hasten the formation of the carbonate. Well, they may have a point . up to a degree. However, just remember what happens when you boil hard water . the carbonates are precipitated out, as anyone in a hard water district will know from scaled pipes and kettles. Chuck the bicarb or shells/chalk in and boil immediately and you will get very little conversion, leave it for a couple of months and can be sure you've done the job fully. Similarly, chuck citric acid in and you will stop the reaction dead in its tracks as it will neutralise the bicarb/carbonate treated solution (each citric acid molecule has no less than three H+ ions to give up . hence its use in scented "bath bombs" to get all that luxurious, soft water that keeps the bubble bath foaming). My money is in listening to those who have achieved very good conversion of the bulk if the ethyl acetate by giving it a week or so to work before distilling.
Mike lists three advantages for stripping runs:
a) Rapidly boiling the wash and condensing everything that is vaporized, without bothering to separate the heads and tails, is an easy way of reducing the volume of liquid you will subsequently process with care, saving a lot of time overall
b) The reduced volume of liquid you get from a stripping run is clear of all solids, salts and dissolved gases.
c) The liquid you get has a very much higher concentration of volatiles, enabling far better separation in the subsequent rectification run as you start out in the middle of the equilibrium chart (the one that plots the concentration of volatiles in the vapor against their concentration in the liquid the vapor came from ... the one that looks like a fat cigar leaning at 45 degrees)
In essence, it is much easier to clean a muddy kid after a football game if you first give the brat a quick hose-down to get rid of most of the mud, and then then shove him in a clean, hot bath with a cake of soap with instructions to wash behind his ears, than it is to try and do it all in a bath full of muddy water. Whiskey distillers, who have to tackle the difficult job of dealing with a mash full of solids, first concentrate on separating the low wines from the mash in a big still, where the only problem is to prevent burning, and then move on to a smaller still where they concentrate on getting the right cut from the clean low wines. Experience has taught them that this is a very effective and efficient procedure that results in a much better product than if they tried to do the whole job in one go. It is definitely well worthwhile.
DP writes more on this, and how it can be used to clear up heads ...
Esters are flavour compounds responsible for many of the characteristic tastes we know very well:
Propyl acetate (Pears)
Octyl acetate (Oranges)
Isoamyl acetate (Banana)
Ethyl butyrate (Pineapple)
Butyl acetate (Apple)
Methyl trans-cinnamate (Strawberry)
(See http://www.leffingwell.com/esters.htm. There are many others and a web search will turn up many more if you're interested.)
Esters are the product of a reaction between an organic acid and an alcohol. Read the back of a wine bottle you'll see wine described as tasting of all sorts of different fruit (except grapes, of course because any fool can do that). Yeast, by its very nature, produces a range of organic acids and a range of alcohols during the fermentation process. These combine to form a range of esters responsible (along with other chemicals) for the flavours in wine that aren't in the original grape juice. This is where the interests of a winemaker differ from someone trying to make clean neutral spirits - winemakers see ester formation as desirable. Yeast makers even advertise their yeasts on how good they are at producing damn esters.
The problem with esters is that a little goes such a long way. Most have detection thresholds measured in parts per billion (ppb). Ethyl butyrate the fruity pineapple ester listed above has an odour detection threshold in water of 1ppb. As a comparison, ethanol in air has an odour detection threshold of about 50 parts per million (ppm). In other words, it's odour is 50,000 times more powerful than ethanol. For those of you obsessed by percentages, your distillate could be 99.9999999% ethyl butyrate free and you'd still be able to smell the damn stuff. Great if that's what you want, bad if you don't.
The ester of the most relevance to home distilling is ethyl acetate. Ethanol oxidises to form acetic acid. Acetic acid and ethanol react to form ethyl acetate. It's no real surprise that you are going to end up with some of this stuff in your brew - yeast puts it there. The good news is its odour detection level is a relatively high for an ester at 5000 ppb (or 0.0005%); the bad news is it has a nasty solvent-like smell you're probably already familiar with. And there's more bad news…
By itself, it boils at 77 degrees, which is pretty close to the boiling point of ethanol. It forms azeotropes with both ethanol and water, and another when all three of them are mixed together (although all at mixture ratios you are never likely to see). I have heard many claims that ethyl acetate can be effectively removed by a still. It's more correct to say that using a still, a good operator can separate the ethanol that contains ethyl acetate (the heads, etc) from the ethanol that doesn't. To me this is not "effective" as the heads contain far more ethanol than anything else and I make ethanol to drink and not tip down the drain. As I said, stills are great for separating alcohol from water, but that doesn't make them the best tool for every job. Removing ester-related flavours with a still has all the finesse of opening walnuts with a sledgehammer. The secret is knowing your enemy:
Food is acidic. Just about everything we eat has a pH less than 7 (See http://www.phsciences.com/about_ph/ph_foods.asp). Acid inhibits bacteria growth and is the environment in which esters are formed. The chemical reaction that produces esters, however, can be reversed when taken out of an acidic environment esters hydrolise back into the acid and alcohol from which they were originally formed. This is why food acids are so often added to preserved food it helps preserve the flavour as well as preventing spoilage.
Ethyl acetate is formed during fermentation. After distillation it's no longer in and acidic environment and starts to decompose back to ethanol and acetic acid. Acetic acid gives vinegar its characteristic taste and although pungent, it's far less detectable than ethyl acetate not great, but less bad. As decompostion produces an acid it tends to slow the rate of further decomposition, but eventually it does happen. If you have the time, people have been getting good results from sticking alcohol in barrels and waiting a decade.
If you don't have the time then don't worry lots of things can be used to speed up the process: agitation/aeration, light (called photodecomposition) do this. The resulting acetic acid has a boiling point of 118 degrees C so it's much easier than ethyl acetate to separate from ethanol in a subsequent distillation. If you add some mild alkali (sodium bicarbonate, sodium carbonate or calcium carbonate) into the mix you can speed up the decomposition time and also precipitate out the acetic acid. By adding a couple of teaspoons of sodium bicarb to your nastiest smelling heads and aerating them with an aquarium pump and air-stone for a week you will end up with something that smells OK. Not quite good enough to drink, but more than good enough to redistil.
This is the real way to solve the ethyl acetate problem not by pouring your (mostly ethanol) heads down the drain. You get to recover all the ethanol that the ethyl acetate had spoiled and (the really elegant part) some of the ethyl acetate is actually turned back into ethanol. The point to remember is the same process will reduce all ester-related flavours, and not just ethyl acetate, including the ones that exist in immeasurable, but still detectable quantities. You don't even need to know what esters they are!! They all breakdown into different components, which you may not particularly want either but will all have less impact on overall flavour than the original ester.
Once I learned this I changed my process to double distil everything. After the first distillation I throw in some sodium carbonate and aerate for a week before distilling again. I don't separate the heads from the second distillation because there's nothing to separate and the result doesn't need carbon filtration. More importantly, nothing I boil off ever goes down the drain - not a single drop. My end-to- end efficiency from sugar to drinkable spirit is 90% with the cost of consumables and wastage very low. Plenty depends on your ingredients, equipment and process, but you get the basic idea.
This is a free type translation/interpretation of a freely available material found on web pages dedicated to production of alcohol at home. There are no claims of any kind for this data.
The first chemical reaction of saponification binds fusel oils and makes it insoluble. In order for this reaction to work, alcohol must be tested for pH. If reaction shows that home made alcohol does contain dissolved acids then regular baking soda should neutralize the reaction. The proportion is 5g~8g of baking soda per each liter of alcohol.
After adding baking soda and stirring it well, potassium permanganate is added. Potassium permanganate should be dissolved in small quantity of clean water beforehand. The ratio is 2g of potassium permanganate dissolved in 50 mL of clean water per each liter of home made alcohol. The mix of alcohol, baking soda and potassium permanganate is stirred well and left alone for 15~20 minutes for reaction to finish.
After this stage is complete, additional baking soda is added to the mix in the same proportion as above, stirred and left alone for 8~12 hours for precipitation of solids.
Next day any sediment is filtered and alcohol goes through the second distillation. This method of removing fusel oils is rather efficient and removes up to 95% of its content.
After the second distillation, home made alcohol is slowly filtered through activated charcoal.