Why my actual FG is much lower than estimated while the actual OG is the same as estimated ?

[Miles_1111]

I just brewed a batch that the measured OG reached the Est OG perfectly, while the measured FG is way lower than the Est:

Est Original Gravity: 1.062 SG 15.21P Measured Original Gravity: 1.062 SG 15.21P
Est Final Gravity: 1.012 SG 3.07P Measured Final Gravity: 1.004 SG 1.03P
Estimated Alcohol by Vol: 6.6 % Actual Alcohol by Vol: 7.6 %

I am thinking maybe is because of these two reasons:
1. My mashing temperature was 63.5 ℃ (146.3℉ ), maybe is too low that created too few unfermentable sugar? so very few sugar left after fermentation?
2. The yeast used was BRY-97. This is a new bag which will be expired in 22 months. The bubble lasted to almost 10 days ( normally the BRY-97 I used just bubble for maximum 5 days ), so this long period of fermentation changed too much sugar into alcohol?

Don't know which one is the main reason or there might be other potential reasons? Please feel free to comment. Appreciate it in advance.

 

[mjlower]

I've run into this problem in the past as well. I don't have any experience with BRY-97 - but I would say the likeliest culprit is your mash temp. 146 is low and will leave you with lots of fermentable sugars, and resulting in a low FG/dry beer. Lately I've been ramping up my mash temps to roughly 152-154 to get my FG in the 1.012 range.

Other things that can come into play would be your mash tun - are you using a cooler tun? If so, you can experience some temperature loss over the course of your hour, so if you start at 146, you may finish around 142-140, creating more sugars..

Your fermentation temperatures can play a role as well - if they get too hot, might be very active, hungry yeast - munching up more than they need..

 

[DarkStarNJ]

Please describe process of measuring gravity and what equipment was used.

 

[brewcat]

Number one would be the low mash temp. I'd think you would need to mash at 156, but 152 would be a good place to start.

Long period of fermentation doesn't matter. The yeast should go until all fermentable sugar is gone.

Also estimated FG isn't quite accurate. For me attenuation will be higher than stated. So the only way to get an accurate FG read is to know the yeast and recipe.

 

[flars]

This is what Fermentis writes in their spec sheets for yeast.
"Fermentis dry brewing yeasts are well known for their ability to produce a large variety of beer styles. In order to compare our strains, we ran fermentation trials in laboratory conditions with a standard wort for all the strains and standard temperature conditions (SafLager: 12°C for 48h then 14°C / SafAle: 20°C). We focused on the following parameters: Alcohol production, residual sugars, flocculation and fermentation kinetic."

The attenuation figures given are for comparing yeasts. These attenuation figures will only match your fermentation if your wort has the same fermentability as their standard wort. Change the per cent attenuation to the actual in your recipe builder when you are getting ready to brew the same beer again. Adjust ingredients, mash temperature, etc for a wort that is less fermentable and finish at a higher SG with the same yeast.

 

[Biscuits]

Another thing to consider, as it happened to me, is mash-out. I was nailing my mash temps, but always over attenuating. Turns out that as i was running off conversion was still happening which gave me more fermentables, thus a lower FG. I started doing a ghetto mash-out (starting the burner as I do my first runnings) and my FG's have been more in line with what I was expecting.

 

[dmtaylor]

I am thinking maybe is because of these two reasons:
1. My mashing temperature was 63.5 ℃ (146.3℉ ), maybe is too low that created too few unfermentable sugar? so very few sugar left after fermentation?
2. The yeast used was BRY-97. This is a new bag which will be expired in 22 months. The bubble lasted to almost 10 days ( normally the BRY-97 I used just bubble for maximum 5 days ), so this long period of fermentation changed too much sugar into alcohol?

1. Yes to the mash temp.
2. No to the yeast, that did not cause this.

As stated in another thread... when's the last time you calibrated your hydrometer? It seems to be reading low maybe.

 

[glugglug]

Are you using a hydrometer or refractometer for fg?

 

[dmtaylor]

EDIT: Oops, nevermind. The new forum setup won't let me delete this.

 

[Miles_1111]

Are you using a hydrometer or refractometer for fg?

A hydrometer is what I use

 

[Miles_1111]

1. Yes to the mash temp.
2. No to the yeast, that did not cause this.

As stated in another thread... when's the last time you calibrated your hydrometer? It seems to be reading low maybe.

How do I calibrate it? I washed the hydrometer every time after using it. It is not electrical.

 

[Miles_1111]

Please describe process of measuring gravity and what equipment was used.

I use a hydrometer. Before I bottled it, just collecedt some 'beer' during the racking by siphon

 

[flars]

Check the calibration with 60°F distilled water. The hydrometer should show 1.000. Some older hydrometers were calibrated for 68°F. The calibration temperature is printed on the card inside the hydrometer.

 

[dmtaylor]

Check the calibration with 60°F distilled water. The hydrometer should show 1.000. Some older hydrometers were calibrated for 68°F. The calibration temperature is printed on the card inside the hydrometer.

This. ^^^ Find out whether your hydrometer reads 1.000 in plain cool water. Mine reads about 1.003 in water, so I have had to subtract 0.003 from every reading I take, for years and years. Yours could be reading high or low. My guess is it reads low and you need to add more points.

 

[Miles_1111]

This. ^^^ Find out whether your hydrometer reads 1.000 in plain cool water. Mine reads about 1.003 in water, so I have had to subtract 0.003 from every reading I take, for years and years. Yours could be reading high or low. My guess is it reads low and you need to add more points.

Mine is a fairly 'new' one. I have used it for a year now, but I will check it anyway. Thanks.

 

[chris000]

Mine is a fairly 'new' one. I have used it for a year now, but I will check it anyway. Thanks.

age of your hydrometer is irrelevant; a shitty one stays a shitty one until the day it breaks...just like a good one.
get water (distilled is better but not really necessary), make sure it is close to the calibration temp that's listed (the difference is not that big; i.e. 0.001 if you compare 68 to 60F). that gives you a one point calibration.
now make a sugar solution (regular table sugar); for example: 25g/100g is 25Brix or 1.1057 and you get your second point.
if you are +/-0.002 on both points I would call it a day, otherwise you should make a chart showing actual vs. reading in between those two points