Alcohol is the product of anaerobic respiration, the consumption of sugars by yeast. If you had access to a chemistry lab, you could measure the alcohol directly, but most calculate their alcohol by calculating the quantity of sugar that has been consumed. For the most part, this is done by comparing the OG to the FG.
In other words, the OG by itself will ...
CO2 in suspension will cause bubbles to come out of the airlock long after the fermentation is done. It is an indicator, but not a precise one.
Experience will tell you that for a particular yeast/wine, fermentation takes, for instance, 5 days to complete if all parameters are identical. Again, it is not precise.
You should get an hydrometer and mesure ...
For something north of electrical tape and south of glass-etching, I've used nail polish. Cheap and easy; even comes with it's own little brush. It won't come off in most circumstances, but it will if you take some acetone to it.
The problem with using anything that etches is that you're removing material from the unit. This can in turn affect the structural integrity in the long run. This is somewhat counter to why people prefer glass fermenters; they will resist scratching better than plastic. Etching is essentially controlled scratching.
A few years ago I took a bumper sticker ...
If you don't want to do refractometry or hydrometry, your next best generic option would be ebulliometry, which is basically measuring the bubble point of the liquid, where the bubble point depends upon how much alcohol is there.
Assuming you're talking about something like this, you could stick it in beer, but it probably won't give you any truly useful information.
The sensors use an enzymatic reaction to determine glucose levels in the liquid. The enzyme, however, is specific to glucose and won't detect any other sugars (for this reason it's really not comparable to a hydrometer)....
To add up on Denny's answer, the density of a solution of sugar and water is (quasi)linear in the range we use in homebrewing (e.g. between 1 and 1.2). (see graph below  where concentration in wt% is equivalent to degree Plato)
Using this graph, you could make a sugar solution with known density by adding sugar into water. E.g. a 5°Plato (5 wt%) solution ...
A vinometer can mesure alcohol of a dry wine (all sugar needs to be fermented). You would need to add some dye to see the results if you have a transparent liquid. It can usually measure between 0 and 20%.
The most reliable way to determine alcohol in any fermented drink, without the need for several thousand US dollars in equipment and some seriously technical laboratory procedures, is distillation.
The answers already given provide good solutions in certain circumstances, but both will give incorrect readings in solutions with significant amounts of ...
Heres a good bit of information from the mad fermentationist about alcohol content and fruit in beer: http://www.themadfermentationist.com/2010/10/adding-fruit-to-beer-increases-alcohol.html
Fruit also contains other things (water) that will further dilute the beer, so the effect will be minimal, if anything at all, and can actually cause the total alcohol ...
I'm also researching the same thing, looking for traits in the wort that indicate how fermentation is progressing and when it's complete.
I don't have any figures, but I would be surprised if the electrical conductivity changes much during fermentation. Conductivity is mainly a result of ions in the wort, which come from the water, brewing salts we add to ...
There are relatively affordable devices (iSpindel and TILT) that continuously report specific gravity wirelessly. You can use the data to derive the alcohol content with a pretty good degree of accuracy.
It's not exactly what you asked for but it wouldn't be too hard to make it work the way you want.
My best guess is that the scale that goes to 26 is degrees Brix, and that one marked in % is potential alcohol. You can test the first guess by making a solution of 10% table sugar. Add 10g of sugar to 90g of water and mix well. The Brix scale should read 10.
Morebeer has a simple table for common fruits,
It is unlikely you will lower the alcohol content unless the addition is primarily water, not at all sweet, or your beer is extremely high alcohol to begin with.
My answer will not be full, but there are some things I can tell:
Splitting half a dollar worth yeast packet in five? Why?! Especially in double-difficult brew, as it is both pretty high gravity (has to be for 10% ABV), and it is mead (no nutrient found in wort)
Nutrient. Why add it in parts? I always understood we want yeast to multiply over as short ...
We make a lot of meads and I think the majority of your process looks pretty good. (Including the staggered nutrient additions). You might want to consider using a blend of nutrients like DAP and Fermaid K. They both contribute different vital compounds.
I suspect that the hop additions pre ferment didn't help you much. That yeast is not very hop ...
Acid content is generally measured by titration - a pH meter or test papers do not measure content only "acidity".
The sourness is IMHO likely to be lactic acid as lactobacillius are generally present on fruit and will work directly on the sugars present. Acetobacter need alcohol (and oxygen) to produce the acetic acid (vinegar) so will generally only work ...
IMHO HPLC is the best method probably followed by spectroscopy. measuring ABV by distillation is "indirect" due to the formation of an azeotropic mixture between alcohol and water. They cannot be separated easily by distillation although one can do a "back calculation" to esttimate (quite accurately) the percentage of alcohol in the original mixture.HPLC ...
If you don't have an hydrometer, just keep a close eye to the airlock and give it a few days (3-5) after the activity has stopped. Mind that this is not the correct way to do that and there's no guarantee that your fermentation has finished.
The only proper way to know that is to take periodic measurements of the density and determine when the gravity has ...
There are sensors that do this. I am not personally familiar with their accuracy, maintenance or robustness.
I am aware of this type of device from Anton-Paar
If you have a beginning gravity and an end gravity, it's pretty easy to figure an approximate ABV for your beverage.
The only way to definitively tell how much alcohol is in a solution is to run it through a
Ebulliometer, which is essentially a tiny alcohol still. Sorry, that's the only real ways to do it!
If you have no other instrumentation, look at the airlock.
If the brew is fermenting, there is always going to be positive pressure against the liquid in the airlock, even when fermentation is relatively slow.
If the room temperature drops and the liquid seems to be creeping back towards the brew, this indicates negative pressure, and suggests that ...
Sugar has about 45 ppg. That's gravity points per pound per gallon. So, one lb. of sugar in one gal. of water will give you a specific gravity of about 1.045. That is the known scale. 2 lb. in 1 gal. gives you 1.090, etc.
Scaling is very simple math and works with all ingredients.
For example if a recipe is for 1 gallon and calls for 4 oz of sugar.
1 Gallon has 3.79 liters, so 1/3.79=.2638 that's your volume %
To scale the sugar 4×.2638=1.055 oz sugar for 1 liter.
You don't have to be so precise, 1oz sugar in this example is close enough.
Determine gravity of honey
Combine a known volume V_w of water with a known volume of honey V_h. measure the gravity of the mixture and denote that quantity g_m.
The gravity of the honey g_h is
g_h = (g_m (V_w + V_h) - V_w) / V_h.
For example, if you mix 1 gallon of honey with 2 gallons of water and measure a specific gravity of g_m = 1.14, then the ...
Grats on your first brew!
This has been well answered on process corrections.
The harsh bitter is from the hop tea, if the cascade was 6.6%AA 60min boil you have about 45 IBUs there which is the top end of pale ales and the start to some IPAs. With no malt to balance, it can taste much more bitter.
At your fermentation temp you can expect some fusel ...
I am going to repeat a lot of what Molot has already said but will add a few extra points:
start with healthy yeast, if possible make a starter at least 24 hours in advance. Use a whole packet at once, maybe use 2 packs.
make sure you have cleaned off all bleach, any left will ruin your brew
add all your nutrients at the start when the yeast need them ...