SG ... idiot's explanation please

[Two_Sheds]

I'm in a right lather about specific gravity. I have read CJJ Berry, and Jack Keller, and someone else, and I just don't get it.

If a recipe says start with an SG of 1080, and my reading was 1010, that's way off, right?

(I added a bag of sugar, which has to be about right, right?)

Now I'm thinking I made a mistake and perhaps the reading was actually 1100

[Hilary B]

Where's Shirley? I can never remember the details of all this stuff, but basically, if you got 1010 before adding sugar, that sounds about right, and a bag of sugar will give a reasonable result.

[Two_Sheds]

No, the reading of 1010 was with 1kg sugar added.
This is what is confusing me. Some recipes say take the reading with all ingredients added, but my instinct tells me to take it before you add sugar, so that you can work out how much sugar to add.

Table wines are generally started at an S.G. of 1.090 or higher and fermented to dryness--0.990 to 1.000. ...The 1.090 specific gravity is a rather magical number. It produces an alcohol level of about 12.3%

The other thing that is confusing my brain is that you start with a high number (1090) and you end up with 1000 (but that is the reading for water????)

[Hazel at the Hill]

Ok - so we start with the premise that yeast feeds on sugar and converts it into alcohol.

Water has an SG of 1.000. Adding sugar to the water raises the SG. As the yeast converts the sugar into alcohol this lowers the SG.

Fruit/veg has some sugar in already, but will need extra sugar to get it at the right sugary-ness for the yeast to have a crack at.

If it is not sugary enough, the yeast will work all the available sugar into alcohol then starve - but there will be too little alcohol in for the wine for it to keep.
If it is too sugary to start with the yeast will 'choke' and not be able to work.

We're aiming at a final alcohol level of about 12%, so complicated sums (which we do not need to worry about) tell us that we need to start with a sugar level giving an SG of about 1.090. As the yeast converts sugar to alcohol the SG will fall and we'd aim for the fermentation finishing with a reading of just under 1.000

I would start with your fruit/veg (boiled/juiced as appropriate), a bag of sugar & fill the bucket up to about a gallon.
Then test the SG.
It's likely to be on the low side, but gives you a starting point. Say the reading is 1.050.
Then you do need to do a sum - adding 4oz sugar raises the SG reading by about 10, so if you want to start with 1.090, thats (4 x 4oz) a pound of sugar.
Disolve the added sugar in the mix, take another reading, then add yeast & nutient and put into a DJ to ferment.

[RedThorn]

Specific Gravity is also known as relative density and to quote...
"Relative density can also help quantify the buoyancy of a substance in a fluid"
Therefore it is possible to have the same SG as water as you are not dealing with a single substance in the liquid eg fruit pulp, sugars etc. The higher the reading the more the sugar content so if you are under the value you are looking for, add more sugar, if you are over the value, you need more water and fruit pulp etc

Now that that is as clear as mud, I hope it helps

EDIT : Hazel types quicker than me lol That post was not there when I( started my 1 fingered typing!) Thanks For a better explanation there Hazel. You got me off the hook there

[Scunny Zeb]

check your hydrometer in plain water (room temprature) to verify its calibrated

[Two_Sheds]

check your hydrometer in plain water (room temprature) to verify its calibrated

I have... and it is

[Hazel at the Hill]

EDIT : Thanks For a better explanation there Hazel. ................

I think that two_sheds will be the judge of that!

[Two_Sheds]

Adding sugar to the water raises the SG. As the yeast converts the sugar into alcohol this lowers the SG.

See, having markings of beer, wine and dessert wine on my hydrometer confuses me. I thought I had to get the reading lower, in order to reach the wine band of the thing.
I didn't know I was aiming to turn wine (1090) into water (1000)

[RedThorn]

Fire water!

[Hazel at the Hill]

See, having markings of beer, wine and dessert wine on my hydrometer confuses me.

Yes, I agree.

Ignore the words, look at the numbers.

[Snadger]

My Relative Density says that my auld Granny didn't have a hydrometer ............but she still made cracking good wine!

[SarzWix]

I've never used a hydrometer! I just follow a recipe, it turns into wine, someone else drinks it. Works for me

[Hilary B]

Getting back to 1.010, I don't think you could get this with a kg of sugar in the gallon (should be about 4oz of sugar in the gallon for that reading).
Water has a SG of 1.000 (some hydrometers show this as 0000, some have the 1 at the front)
Sugar syrup has a higher SG (depending how much sugar there is)
Alcohol actually has a SG below 1, which is why a strong dry wine may read 0.998 (or even lower).
You are turning sugar into alcohol, so the SG goes down, potentially below the 'water' reading.
If you end up with wine that has some sugar in, it might read 1.010.

[bobleponge]

I've never used a hydrometer.
But then, I've never made wine that you can actually drink...