Low final gravity (1.008); possible causes?

[GlowingApple]

I'm trying a new recipe. It's intended to clone Empyrean's (a Nebraska-based brewery) Burning Skye, a Scottish Ale.

I started with an OG of 1.058, fermented with S-04. From BrewTarget I was expecting a FG of about 1.014, but ended up with a FG of 1.008. The brew tastes a little watery, but doesn't taste wholly unbalanced.

My question is what might have caused such a low FG? I don't think it's infection. There was no visible pellicle, and other than a bit watery it tastes just fine. I brewed a chocolate stout the following weekend that turned out just as good as (and very similar gravities to) the previous time I brewed it. Unless it's that particular secondary fermenter, my equipment and sterilization procedure was the same (soak with oxyclean overnight, sanitize with StarSan on brewday).

I bottled a few and kegged the rest and will let it age a month before I try it again. I am more than willing to RDWHAHB, but I'm just curious if anyone has any ideas!

Here's the recipe:

Yeast: S04

1/3 oz Nugget, boiled 60 min (13.3% α acid)
1/2 oz Cascade, boiled 15 min (6.9% α acid)
1/2 oz Cascade, dry-hopped in secondary

6 lbs. Pilsen Light Dry Malt Extract

1/4 lb Honey malt
1/4 lb Smoked malt
1/4 lb Biscuit malt
1/2 lb Caramel 60 malt
1/2 lb Chocolate wheat

3-gallon boil; diluted to 5 gallons. Pitched yeast dry and fermented at around 76 ˚F (my apartment stays warm, and is hard to control, even in the winter).​

 

[wbarber69]

Yeast cleans up fast at or above 72degrees f. I have a couple ale recipes that call for a final of .09 but I usually achieve this because those particular recipes use a fair amount of honey, giving the yeasties plenty of food. I control my temps, keeping ales around 68 then once fermentation slows I raise them up to 72 to let the yeast finish up before crashing. If you're not looking to get down below 1.014 from a relatively high 1.058 I'd try to get those temps down a bit. You may even find it enhances the flavor of your beers and reduces those pesky initial esters that we try to avoid.

 

[GlowingApple]

I generally tend to brew fairly heavy dark beers (OG's above 1.065), so maybe I'm just not used to the effect temperature has on lower gravity beers. I did brew a Hefeweizen with an OG of 1.056, FG of 1.012, but I was using SafBrew WB-06, and it's a wheat beer, so not sure how much that changes things.

I live in an apartment and have a bear of a time controlling temperature. I actually never heat my apartment in winter and often open my windows to cool it down below 80 ˚F... At some point I'd like to build a temperature controlled chamber/fridge, but unfortunately I don't have the space or the money at the moment, and at some point hopefully will be in a house and have a basement I can use!

I've brewed a number of other beers under these conditions and haven't gotten this low of a FG before, but like I said most were higher on OG. I do get an appreciable amount of ester flavors (or I assume more than I would get at lower temps), but aging works wonders.

 

[wbarber69]

Hmmm. I've always seen lower fg from my higher gravity beers. Have you ever tried a swamp cooler? Its the closest thing you can get to ferm control without coming out of pocket too hard. Hell you probably have everything you need. Some sort of container to hold your carboy/bucket, water, and frozen water bottles.

 

[GlowingApple]

Yeah, my darker beers tend to be pretty consistent:

OG 1.066, FG 1.016 (made this stout three times with approximately the same gravities, and the same yeast as the beer in this thread)
OG 1.067, FG 1.015 (whiskey barrel stout)
OG 1.064, FG 1.016 (porter)

Both of my lower gravity beers were wheat beers and came out about right:

OG 1.057, FG 1.014 (dunkleweizen)
OG 1.056, FG 1.012 (hefeweizen)

I set the fermenter inside a rubbermaid tote, just in case it spills over I don't want to damage the carpet, so a swamp cooler would be pretty easy. I never thought about that before, but I'll definitely give that a try next time!

 

[seagondollar]

Disregard.

 

[masonsjax]

Lack of pellicle doesn't mean it's not infected. I'm not saying your batch is infected, just pointing out that fact. However, there are a lot of wild yeasts and brett strains especially that can attenuate way past what sacc alone can, so that is a possibility. Wort composition, fermentability is another factor that can affect the FG. Maybe that brand of extract is unusually high in short chain sugars.

 

[lilbova3]

Even though you might not be looking for this in your beer but a low final gravity would just lead to a drier finish. It might not be a terrible thing. You could have over pitched as well. That's my two cents.

 

[GlowingApple]

Lack of pellicle doesn't mean it's not infected.

I did not know that! Every beer that I've seen infected (from friends and online) has had a pellicle so I just assumed. I don't think it's infected either since, other than a bit dry and lacking some mouthfeel, it tastes just fine.

I usually use the darker extracts (such as amber) so maybe this brand's extra light does have more short chain sugars. At some point I'd like to start doing all-grain so I'll have some more control over this.

Even though you might not be looking for this in your beer but a low final gravity would just lead to a drier finish. It might not be a terrible thing.

Yeah, that's what I'm thinking too. This style of beer isn't meant to be very heavy. It does taste a little watery now (seems like it could use a little more mouthfeel), but that could change once the carbonation is better and it has aged for a bit.

I used a single packet of dry yeast for 5 gallons, which is what I always use. I'm used to brewing higher gravity beers though; for a lower OG is it better to pitch less yeast?

 

[lilbova3]

Yeah, that's what I'm thinking too. This style of beer isn't meant to be very heavy. It does taste a little watery now (seems like it could use a little more mouthfeel), but that could change once the carbonation is better and it has aged for a bit.

I used a single packet of dry yeast for 5 gallons, which is what I always use. I'm used to brewing higher gravity beers though; for a lower OG is it better to pitch less yeast?

Personally, looking at your DME and malts used I wouldn't expect too much of a mouthfeel. The wheat could add some but if you want a velvety mouthfeel like you get in some great stouts make sure to add some flaked oats. You won't get much mouthfeel in relation to gravity. Remember, the gravity number is letting you know how much sugar is still in the beer. A higher FG will be sweeter and maltier than a lower FG.

I would say it's always recommended to pitch the correct amount of yeast. Doing some research, Mr. Malty believes there's 20 billion yeast cells in a gram of dry yeast, Brewer's Friend believes there's closer to 8 billion in dry yeast. Since this finished with such a lower gravity I'd say Mr. Malty might be correct. More yeast available to eat the sugar will lead to a lower FG. I agree with wbarber69 that the higher temp could have caused the low FG as well. I'd just make note of it for this beer and other subsequent beers in this OG range that they will finish with a lower FG with that much yeast pitched.