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As you probably already know, this question is usually about the fact that aluminum is chemically more reactive than stainless, so that certain chemical conditions in the pot can rise to having traces of aluminum compounds in your mash. Up until abouut 10 years ago, I did almost all of my distilling in aluminum pots, and much of the mashing.
To prove to myself that it was ok, I searched the web pretty exhaustively to see if any volatile, that is to say “capable of being evaporated”, aluminum compounds known to chemistry. The only ones that I found were lab curiosities, that could only be made in a lab under very difficult to achieve conditions. My point in this is that if the aluminum compounds can’t become vapor, they’ll never come across with the vapor in a still.
That doesn’t mean I’d brew beer in aluminum, but it’s ok for stilling. Some people will object to this, but often they are people who drink highly-acidic soft drinks from aluminum cans,
The life cycle of yeast can be considered to have 4 major phases, each phase with its own requirements and products.
First, for dry yeast, there is the hydration stage. In the presence of water , the dried yeast cells reconstitute, and are helped greatly by “hydration nutrients” at this point.
Second is the multiplication or growth stage. This is when the yeast cells multiply by budding, increasing their numbers by a large factor. At this point, the yeast metabolizes sugars to water (no ethanol) and carbon dioxide. During this phase oxygen is vital, and required to make the lipids for new cell walls. Normal yeast nutrients are also necessary at this point.
The third stage is our favorite. After stage 2 has consumed all the oxygen (aerobically), the yeast kicks into its oxygen-less (anaerobic) stage, where it now metabolizes sugars into carbon dioxide and ethanol. It still needs yeast nutrients in this stage.
Fourth stage is where the yeast has eaten all the sugar, and just quits, clumping together (flocculation) and settles to the bottom of your fermenter, ready to be revived for another fermentation.
To sum it up, oxygen is necessary at first, and then its absence is necessary so we can get ethanol. You can leave your fermenter open, if you figure you’re safe from wild infections, and can determine whether your ferment is finished by taste or specific gravity, but an airlock keeps you safe from infection and tells you (by bubble frequency) where your fermentation is in the process.
Anything that I bottle to keep for a while, I figure needs to be free of infections so I airlock and disinfect, but for distillation, I’ll often just throw a towel over the fermenter to keep fruit flies and cats out. Once the still’s fired up, everything‘s sterile.
Yes, that’s my book. It’s mostly aimed at beginning potstillers.
Aeration is really only important to replace oxygen in the wash, to replace oxygen driven off by boiling or heating. The yeast needs the oxygen to build new cell walls in the yeast’s reproduction/growing phase. I don’t know how you produce your cider, but my process is entirely cold, so no oxygen is lost due to heat. Not only that, but the crushing, draining (from pressing) and pouring into jugs or carboys, aerates the cider some also. For me, at least, I don’t additionally aerate my cider.
“Pitching” yeast is just the introduction of yeast to your fermentable liquid.
Because apple juice typically ferments to between 5 and 8% Alcohol By Volume (%ABV), you’ll get less alcohol in the distillate than some of the higher %ABV washes, like grape wine, for instance, or a sugar wash. If you mix a gallon of, say 7% hard cider with a 5th of maybe 40% Calvados, you’ll have a total (in fluid ounces) of (26)(.4) + (128)(.07) = 10.4 + 8.96 = 19.36 ounces of ethanol.
As a strictly ballpark estimate, if you distill that mixture to a final head temperature of 98 or 99C (208 or 210F) you will, for all practical purposes have all that ~19 ounces of ethanol in your collected distillate. Again very roughly, if you mixed all of your distillate together (which I don’t recommend – this is for calculations’s sake), that total distillate would be about 50% ethanol, so your total output would be twice that 19 ounces, or 38 ounces of total distillate.
For yet again a great handwaving approximation, perhaps 3/5 of that total you will save as hearts, that spirit which tastes good to you, and 3/5 of 38 is about 23 fluid ounces, not quite a pint and a half. You will probably have to add a bit of water to that amount, to get the drinking strength you want, so that pint-and-a-half will grow a bit. Depending on lots of things, your actual results will vary from that, but the upside is that homemade Calvados is delicious!
A couple of things occur to me. When you say ” I cook the mash then let it cool down to about 70 degrees” did you really boil all the grains, or did you actually mash the grains, heating the water and grain to 150-155F to allow the enzymes in the barley malt to convert the starches in both the barley and the flaked corn to fermentable sugars? Simply boiling the grain will “kill” the enzymes, so that the only sugar in your wash will be that 4 pounds of sugar, plus whatever small amout of starch got converted to sugar before the temperature hit ~160F. That could give you enough sugar for a 7% wash, but with entirely different SG numbers. All that corn will be for almost nothing.
By the way, how did you measure that 7% ethanol in the wash. Without OG and FG, most distillers or brewers do not have any way to measure the ethanol % at end of ferment.
If your SG really was 1.110, as Richard pointed out, yeast can have problems surviving that wash, and in the process, can make some nasty-tasting distillate, and that may be what you’re seeing. For best flavors, especially at first, I’d stay below 1.085. Often washes that give you the most ethanol will give you the worst-tasting distillate.
You also say the head temperatures “kept it around 190”. That tells me that either you were operating a reflux still, with its reflux condenser at the top of the column, or you were operating a potstill, and have an imperfect understanding of what happens with potstill head temperatures.
In a potstill, as you apply heat to the wash, the wash rises to its boiling point, which is only determined by its ethanol content, and is in no way controllable by the operator. When the wash boils, the vapor leaving the wash is at exactly the temperature of the boiling wash, and therefore also not operator-controllable. As the ethanol-rich vapor boils off, the ethanol content of the wash decreases, and the head temperature follows a very predictable slowly increasing curve limited by the boiling point of water. At no point can the operator change the head temperature from where physics is taking it. Ok, if you stop the boiling, you can reduce the head temperature, but you’ve also stopped distillation.
Not sure if this is what you are asking, but a potstill that is relatively easy to build is quite capable of matching or exceeding the quality of most of the best liquors (not just ethanol) out there. The best single malts and (to me) best bourbons out there are made on potstills. Admittedly, the techno-stills (column, continuous, valved plated, reflux) make the job easier, more efficient in terms of time, energy, and ease of use, and expertise, but they don’t make the spirit better.
Of course, running a potstill takes some time, but it will never shortchange you with respect to liquor quality for fine spirits. On the other hand, if all you want is the ideal American vodka, simply ethanol and water, you really need a potstill.