Can calculated final gravity be this wrong?

[Mechphisto]

I created and brewed my first recipe, using both BeerSmith and BrewersFriend.

They calculated my OG and FG to be:
1.060/1.054 and 1.017/1.010 respectively.

My actual OG was: 1.065
But for the last TEN days my gravity has been 1.024 (at 70F).

I think it's safe to assume that primary is done! But, I'm still leery of making bottle bombs, because 1.024 is a far cry from 1.017! Is it possible for both software to be that wrong?

Can I ignore that, and be pretty certain that all primary is indeed quite done and it's safe to bottle?

Thanks for any feedback!
Liam

 

[BGHSmt7]

What temperature did you mash at, did you caramelize any sugars during the boil, and what yeast did you use? The discrepancy seems quite large, but we would need som e more information to help decifer.

 

[Mechphisto]

What temperature did you mash at, did you caramelize any sugars during the boil, and what yeast did you use? The discrepancy seems quite large, but we would need som e more information to help decifer.

Ah, well, below is my exact recipe and temperature info.
I didn't caramelize any sugars that I know of... I took it off heat when adding any sugar/malt and let dissolve before putting back on heat.

10.24 oz	Caramel Malt - Crystal 80L (Great Western)	155 deg 30 min
8.4 oz	Black Patent Malt	155 deg 30 min
4.1 oz	British Roasted Barley	155 deg 30 min
4.1 oz	British Malted Oats	155 deg 30 min
			(remove grains, bring to boil, then off heat)
3.3 lbs	Dark Liquid Malt Extract (LME)	Dissolve then Boil 60 min
1 oz	Northern Brewer	Hop	Boil in bag 60 min
1 oz	Fuggles (4.50%)	Hop	Boil in bag 60 min
3.3 lbs	Dark Liquid Malt Extract (LME)	Dissolve then Boil 15 min
1 lbs	Lactose	Sugar	Dissolve then Boil 15 min
.5 lbs	Corn Sugar (glucose)	Sugar	Dissolve then Boil 10 min
1 pkg	ClarityFerm	Clarifier	Pitch with yeast
1 pkg	Safale US-05	Yeast	Pitch at 67F

 

[Frodo]

There often seems to be an FG threshold around 1.020 with many extracts, especially liquid malt extract and especially with dark liquid malt extract. You're probably safe bottling if SG is stable for a couple/few days.

 

[Mechphisto]

There often seems to be an FG threshold around 1.020 with many extracts, especially liquid malt extract and especially with dark liquid malt extract. You're probably safe bottling if SG is stable for a couple/few days.

Ah! OK, good to know -- I didn't know that.

And it's been entirely stable for 10 days! So, yep.

 

[Yooper]

Ah! OK, good to know -- I didn't know that.

And it's been entirely stable for 10 days! So, yep.

Yes, the dark extract isn't very fermentable, and the lactose adds 9 points to the gravity because it's totally non-fermentable. So it sounds done.

The way software works is by calculating 75% (or whatever) of the OG, so it's a best guess at best.

 

[BlueHouseBrewhaus]

+1^ As Yooper said, the lactose will bump your FG up considerably. Not sure about Brewers Friend but in BeerSmith you need to be sure to check the box for "Not Fermentable" in the Edit Grain Details window for lactose. Otherwise, it will calculate your FG as if the lactose were regular sugar.