OG, ABV decreasing in fermentation

So I have an IPA going in the primary right now, been there about 4 days. Everything is going fine, regular bubbling in the airlock, nice krausen foam on top.

I took a sample earlier to measure the ABV and OG with my hydrometer. Appears to have gone down a ton since the day of the brew. The ABV decreased from 9% to 4.5%. Is this normal, will it start to increase as it ferments longer or am I just going to have a weak brew?

OG (Original Gravity) measures the amount of sugar in the wort. Gravity will go down as the yeast eat the sugar and fart out alcohol. So all is going well.

To see the final ABV you take the original OG (redundant) and subtract the FG (Final Gravity . . normally about 1.012) and multiply by .131 (I think).

The ABV you are looking at is just an idea of what you brew COULD have at the very beginning and is not used . . . ever (actually).

So 1.055 - 1.012 = 43
43 * .131 = 5.63% ABV

I assume you are reading the side that gives the alcohol % on the one side. If that is the case, you need to look on the side that measures the gravity points starting @ 1.000 and reading up in (.100) increments.

Example would be before fermentation the hydrometer would float high and around (just an average for the sake of this response) 1.050

After fermentation is complete, it would read lower EX. 1.012 and the hydrometer would float lower in the wort.

Does this help?

If you are reading the ABV on the hydrometer that wont tell you what you need to know. To get ABV take your starting gravity just prior to pitching your yeast, then approx 7-10 days later when the FG has stabelized take your finished gravity. Subtract you finished garvity from you starting gravity and multiply by .131 that will be you ABV...


wow i type slow..... well said grinder.

Yes. I wrote down the gravity points but they're at home on a sheet of paper. Those numbers decreased as well.
From what I gather, you want it to decrease so I am doing just fine. I guess a better question may be what is an optimal OG for an IPA?

Stoopidwon said:

To get ABV take your starting gravity just prior to pitching your yeast, then approx 7-10 days later when the FG has stabelized take your finished gravity. Subtract you finished garvity from you starting gravity and multiply by .131 that will be you ABV...

Click to expand...

OK great. Looks like I was just calculating it wrong. I'll go home and do those calculations. Thanks.

i don't think there's an 'optimal' gravity for an IPA (i mean, there are style guidelines, but you don't HAVE to follow them). but somehwere in the neighborhood of 1.055-1.065 should be a good starting point. but don't let your OG sway you, i'm sure it'll turn out fine.

Background info: alcohol is less dense than water, water is less dense than wort. As the sugars in the wort are converted to alcohol, the gravity decreases. When it stops decreasing you've got beer! Green beer, but beer none the less.

You started around 1.068, which is at the high-end for an IPA and should end up at 1.015-1.018.

If you want to read the ABV scale, just subtract ABV at the end from ABV at the start to get your actual ABV.

So, if your beer started at 9% and is down to 4.5%, then you already have (9-4.5)=4.5% alcohol in the beer! If it drops down to 3.5%, then you will have (9-3.5)=5.5% ABV beer. Basically, the higher it starts, and the more it drops, the more alcohol you get.