hydrometer questions

[columbian]

I'm trying to get my hydrometer knowledge up to speed.

Can anyone tell me what the three different scales measure? I know the one with a 1.00 at the top is specific gravity, but what are the other two?

Can the hydrometer give me any clue of my present alcohol level if I didn't use it before fermenting? I'd think any level below 1.00 would indicate the presence of any less-dense-than-water substance in there, and that could only be alcohol, right?

I understand that the SG of a liquid increases as things like sugar are dissolved in the liquid, but does the presence of undissolved solids (yeast--live or dead--, various apple solids, dirt, bugs, etc) affect the SG?

I just racked my carboy of cider, and there is a about 8 inches of air between the cider and the top of the secondary. Is this a problem? I was thnking it would start fermenting again, at least a little, and the space would fill up with CO2, but that's not happening. What should I do? would it be right to dump some unfermented cider in to try to get it to start fermenting again?



Thanks for any help.

 

[manoaction]

Can anyone tell me what the three different scales measure? I know the one with a 1.00 at the top is specific gravity, but what are the other two?

They are plato and potential alcohol. All three measure the same thing… Sugar content. While I’ve heard well reasoned arguments for using plato over specific gravity, there isn’t any reason to switch in the early stages of this hobby. The potential alcohol can be handy for rough estimations of alcohol content. Subtract the final potential alcohol from the original potential alcohol for a rough estimation of your ABV.

Can the hydrometer give me any clue of my present alcohol level if I didn't use it before fermenting? I'd think any level below 1.00 would indicate the presence of any less-dense-than-water substance in there, and that could only be alcohol, right?

Nope, beer hydrometers are meant to measure the sugar content which we can use to calculate alcohol content, but you can’t use your ordinary hydrometer for measuring alcohol in beer if you don’t have comparative measurements.

I understand that the SG of a liquid increases as things like sugar are dissolved in the liquid, but does the presence of undissolved solids (yeast--live or dead--, various apple solids, dirt, bugs, etc) affect the SG?

Not under normal circumstances. You’re measuring the weight of the displaced fluid so the only thing that counts is what’s dissolved into the water. Other undissolved solids don't add to the density of the fluid, they merely displace it the same way your hydrometer does.

I just racked my carboy of cider, and there is a about 8 inches of air between the cider and the top of the secondary. Is this a problem? I was thnking it would start fermenting again, at least a little, and the space would fill up with CO2, but that's not happening. What should I do? would it be right to dump some unfermented cider in to try to get it to start fermenting again?

Unless you’re planning on aging it for a very long time, I wouldn’t worry about it. You’ll be fine if you’re only planning on keeping it in there for a few weeks. Otherwise your idea about the addition of unfermented cider or a brown sugar solution isn’t a bad one.

 

[columbian]

Mano':

Thanks for this information.

I'd not recalled that the Hydro is measuring the weight of the displaced fluid. That clarifies things a lot.

I already opted for caution, and racked into four and a fraction gals, all but one pretty clear.

I guess I'll have to drink it no matter how strong it is. I'll be smarter next time.

But it does seem to me that if the hydrometer drops so far there's a half inch of liquid above its top, that would be a good sign.

If I get another dry day, I'll try picking some more apples and see if I can get another batch going.

 

[gregbathurst]

The other 2 scales on the hydrometer are known as baume and brix. Baume measures the potential alcohol of wine or cider, to do the same for beer you deduct the final baume from the initial. Because the baume scale was designed for wine it may not be accurate for beer. Brix is the sugar content ie 1 brix = 1g sugar in 100ml of solution. Winemakers use baume and fruitgrowers use brix, brewers use sg.
I use a baume hydrometer, it is a lot easier than sg, if my juice is 6.5 be I know it will be 6.5% alcohol, I can ignore all the 1s and zeros of sg.