OG was too low, how does it affect FG?

[torontosudz]

I'm doing a Baltic porter that was meant to be - 1.057 OG but ended up being 1.045; it's partial boil extract so I suppose I added too much water to the wort.

It's sitting at 1.018 right now so I'm wondering if I need to repitch and/or if I bottle will this be a bomb risk? Meant to be given as a gift so that's not really a nice present if it explodes

 

[Euphist]

It's possible that your OG was fine...it's not uncommon to get off readings from extract beers due to incomplete mixing of the top-off water. (no worries - fermentation will finish mixing it for you.) As far as when to bottle...take readings for the next couple of days. If it hasn't changed from today's reading, it should be safe to bottle.

 

[Calder]

Lets assume your OG reading was wrong (which it probably was as noted by Euphist - and I agree with).

1.018 would be almost 70% attenuation.

Depending on your recipe and yeast, you may be done.

 

[Pie_Man]

As pointed out, partial boils are notorious for inaccurate OG readings. Search through the forum and you'll find hundreds of similar threads (even when people think they mixed it up "really well").

With partial boils, it's far more accurate to compute the estimated OG based off of your recipe, http://www.howtobrew.com/section1/chapter3-4.html.