OG falling short

First, is it the OG that's lower than expected? Or is the FG higher than expected? Either way, you'll need to describe the recipe and your process for anyone to help.

 

Most probable causes:

1) If you measure specific gravity at any temperature above 70 F, you need to adjust for the temperature difference as the two variables are inversely proportional. In other words, the hotter it is, the lower the reading will be and you’ll have to add up to 0.020, 0.030, or whatever depending on temperature.

2) Otherwise it’s probably the crush. Did you have your grains milled at a homebrew shop? They are notorious for setting the mill gap way too wide, resulting in low efficiency and more malt sold. They say it’s because they want to avoid complaints of stuck mashes, but my guess is that it’s for a more profitable reason. Get your own mill and set the mill gap tighter, and your efficiency will skyrocket.

It could be something else, but those two things are the first ones to look at and will resolve probably 75% of all efficiency problems.

EDIT: After reading the original post again, I should point out that I've assumed that this is an OG problem, and not an FG problem. If your FG is actually the problem and not the OG, then let us know the recipes used and I'll respond again.

 

Also, in addition to knowing your process to help the homebrew pros out, I would suggest testing you Hydrometer in distilled water.

 

Yep, that's another key thing.

 

If you meant to say the SG doesn't match the projected FG, how much liquid do you have in the fermentor compared to what the recipe calls for? Too much wort will give you a lower FG, and too little wort will cause your FG to be too high.

 

What was the recipe, including mash temperature and mash length? What was the actual OG and actual FG?

BTW, OG is the SG before fermentation. The FG is the SG after fermentation. I.e. when you say SG, nobody will know what you mean, unless it's obvious from the context.

 

I think people are just confused by the terminology. On this forum, generally:

SG = specific gravity
OG = original gravity
FG = final gravity

You'll probably have to give us a lot more information before we can give you any helpful advice.

 

Okay, with that grain bill and yeast strain, along with those mash parameters, you should have got a lot more attenuation, i.e. lower FG. Let's look at the factors individually.

Grain Bill: assuming your supplier sold you the right grains (i.e. that the Golden Promise was really Golden Promise), there should be no problem there. At any rate, I can't think of a grain that could have been subbed in that would have had the diastatic power to convert the mash, but with such low fermentability.

Yeast Strain: What was the batch size and how much yeast did you pitch? How old was the yeast? How had it been stored?

Mash Length: I'm sure you can tell time, so no problem there!

Mash Temp: The most likely culprit, IMO. How did you measure the temperature of the mash? What kind of thermometer? Is the thermometer calibrated?

Two final questions: How long was the fermentation and at what temperature? And how did you determine it was finished?

 

As much as I want to love Golden Promise, each time I have used it thus far, I have been over my target FG. It came from the same location, so I am not sure if it was them or what, but I did ask for double crushing the grains the last time I got it. Next time I will try a different shop for it or see if my LHBS can bring some in for me.

Not saying that is the OPs issue, just something I have noticed in my GP experiences...

 

How do you measure your FG? Hydrometer or refractometer?

 

How far off was your FG? A wort with Golden Promise does attenuate a little bit less than a wort with, say, pilsner or brewer's 2-row. But the difference is pretty small. That said, most programs/calculators don't take the composition of the grain bill into consideration when predicting attenuation/FG. It can be pretty significant when there are non trivial amounts of grains like crystal malts and dark roasted malts.

In the OP's case, the attenuation is way out of whack. Hard to imagine it being the malt's fault.

The crush will affect mash efficiency, but it won't really affect attenuation.

 

What's the fermentation temperature? Also, did you see @invertalon's question? If you are using a refractometer, the readings need to be adjusted using a refractometer calculator.

 

Have you verified the mash temp with a known good thermometer?

 

And are you using a refractometer calculator? If not, that's the problem, and your true FG is probably fine.