How To Determine Starting Specific Gravity

ptech

Assuming all environmental variables remain favorable (e.g. PH, temperature, nutrient levels, etc), after the fermentation is bubbling fiercely and the yeast are thriving, the fermentation eventually stops (or dramatically slows) for one of two reasons right?
1) the ABV gets too high for the specific tolerance of the yeast, thereby killing the yeast (some yeast die at a lower ABV than others)
2) there's simply no more fermentable sugar in the mix so the fermentation slows down dramatically due to no more fermentable sugars in the mix (the yeast continue to live a little while beyond this point due to other reasons)
Assuming all environmental variables remain favorable (e.g. PH, temperature, nutrient levels, etc), we seem to have a choice as to what stops our fermentation:
This means that we can control and decide which of the above two reasons will be the cause that stops our fermentation.  We can control this by setting the starting specific gravity at a specific level.   That all said, which of the two above causes should be the one we choose in order to produce the best quality product.  We can't simply say that all yeasts should start at a specific gravity of 1.070....I'm not going to buy that answer after all I've read.
thanks,
ptech"..Almost seems like a miracle every time that first drop of alcohol comes out of the still.." ...Rad14701

NcHooch

almost all modern brewing yeasts can ferment a wort to 10% abc without producing an excessive amount of off flavors, and these yeasts should be able to ferment to near 1.01 fg
Maybe I'm misunderstanding, but you should not be attempting to control your fermentation by killing off your yeast with alcohol ...that is exactly why these 20% turbo yeast recipes are so foul.NChooch
Practice safe distillin and keep your hobby under your hat.

Prairiepiss

If you are trying to control it with starting SG. So that the amount of alcohol kills off the yeast. You are wasting sugar. This is good for wine. Where you want it to end up sweeter then normal. But for our purposes its a waste of money. Not to mention if your taking it high enough to kill off the yeast. They will be stressed. Giving off off flavors and smells that will hamper the amount of usable product.
The stating SG should be determined per different recipes. So that the best product is made for that recipe. Usually trial and error is the only way to figure this out. Comparing flavors, smells, amounts of usable product to the amount of unusable product.It'snotsocoldnow.
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ptech

I'm very glad to see that y'all seem to be in agreement with the various texts I've been reading (that #2 is best).  They don't spell it out the way I did above but they all seem to indicate that answer two above is the preferred cause that should end the fermentation.  
There is a third option which is the following;
3) set the Original Specific Gravity high enough so that you can stop the fermentation before the SG gets too low (e.g. 1.015) but still being able to achieve  the final ABV that is best for the specific yeast being used.
I've read of some yeasts that die at 8% while others at 14, or 18 or more, but the one I'm using goes up to 12%. So these differences in yeast should give rise to the main subject of this topic.
After my readings, I began to think that method two above is the preferred method.  But since none of the texts were clear enough for my "dummy" style of reading, I'm glad I asked and even happier that y'all agree with number 2.
kind thanks,
ptech"..Almost seems like a miracle every time that first drop of alcohol comes out of the still.." ...Rad14701

Dnderhead

just because a yeast can ferment to 12%? does not mean you should.
this is "pushing" the yeast to its limits and can cause problems.
such as off taste and stalled ferments.

Usge

Just made some tangerine wine.  Fermented out dry to around 13% (a little high actually for this kind of wine), usually sugar/sweetening is added after the fermentation just before bottling to taste. But, you have to stop the yeast first...and they use potassium sorbate for that. The yeast will just fall right out. It helps clear it and keeps it from carbonating in the bottle.
If you have a ferment that just won't quite clear (or give up) and keeps working...you coudl also put it somewhere very cold. That will usually also drop the yeast right out.  But, these are more issues you deal with.  Mostly...I think people target the SG they want...or potential alc they want up front..such that when the fermentation is finished...they have achieved what they want.  There's always some variables...but that's generally how recipes are developed afaik.  There are lots of "unplanned" things that can end a fermentation early as well (like bacteria)

Hebden

Revitalising an old thread here because I am interested in starting SG and how to control it in relation "to my" bill, I am very much a newbie, but I was given a little advice which I would like to try and follow (quoted below), but I am not entirely sure how to follow it.
My sugar wash Bill:-
145L drum wash
23kg sugar
500g bakers yeast
4 x B12
4 x B12 complex
1/2 tsp Epson salts
3.3 tbsp DAP
295g CaCO3
pitched at 91f
Start SG = 1.053    Pitched = 91f
Fermented out to ~8.35%abv
Final SG 0.988
I would have liked to raise final alcohol content to closer to 10% - how do I do this, I believe it is just additional sugar, from what I can tell my yeasties were happy, next run I will be using EC-1118.
My aim here is still to achieve a very clean neutral btw not that bakers was bad, I just want to try these things for my own knowledge.
Is there any formula or educated guesswork to say that given my above bill rather than my sticking my finger in my ear and thinking hard.
Would an extra 1kg, 5kg or 10kg sugar get my opening SG to say 1.060, 1.070 or 1.080?
Thomas, I am trying your suggestion, if nothing else, it is great to try new things to expand my knowledge.
How can you calculate what the final gravity will be "when dry" before completion, surely the final gravity changes every run, or is the final gravity regularly consistant with a given recipe?

ThomasBrewer

How can you calculate what the final gravity will be "when dry" before completion, surely the final gravity changes every run, or is the final gravity regularly consistant with a given recipe?Hi Hebden. Since you're using sugar, you can assume that your wash is "fully fermentable" and will eventually reach 1.000-0.998. Simply keep adding sugar until you reach your target OG. Assuming healthy yeast, you'll have consistent results batch-to-batch.
The parent site has a real simple calculator: https://homedistiller.org/wiki/htm/calc ... gar_sg.htm
The calculator gives the following numbers for your wash:
23kg sugar added to 147L of water should give 161L total volume of 1.055 SG wash. You're a running a little less efficiently for some reason (possibly your sugar is damp and skewing weight?).

Demy

The easiest way for what you want to do is to use an online app or calculator, or a webapp or homebrewing software. The other way is to calculate by hand.... the sugar in any case is to be considered 100% fermentable and 100% efficiency