Consistently Low Final Gravities

[robopp]

I'm a small batch brewer - 1.2 gallons per batch. I use a 2 gallon bucket as my primary and a glass gallon jug as a secondary (fyi - the glass jug volume is actually around 1.15 gallons). I have a 3 gallon cooler for my mash tun and I use a digital pen thermometer for my mash temperatures. I mainly brew big IPAs - 90 minute, gandhi-bot, maharaja, etc. My problem is that I'm chronically getting lower than expected final gravities. To attempt to counter act the low final gravity, I've started bumping up the recipe's mash temperature by a couple degrees with little success. For instance, if the recipe calls for a mash temp of 150, I'll aim for 152. I check the temperature of the wort after the first running's and it's only a couple degrees off. Also, I use a hydrometer for my final gravity measurement and either S-05 or S-04 for the yeast.

Examples -

90 Minute Clone - OG: 1.080 FG: 1.008
Gandhi-bot Clone - OG: 1.061 FG: 1.006

I look down the list in my brew journal and almost everything is well below 1.010. What am I doing wrong?

 

[farmskis]

What does the grain bill look like?

 

[BackAlley]

That's like a 90% attenuation. Are you sure your hydrometer is accurate? (Check with distilled water). Also, is it the taste you're not satisfied with or just the number.


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[balazs]

Have you calibrated your thermometer. It may be reading high? You may think your mashing at 152 and it is really at 149.

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[robopp]

What does the grain bill look like?

Here are the grain bills:

90 Minute Clone:

3.4 lb American - Pale 2-Row 94.4%
0.2 lb United Kingdom - Amber 5.6%

Mash in a 152F with a thickness of 1.5qt/lb

Gandhi-bot Clone:

3.2 lb American - Pale 2-Row 90.1%
0.2 lb American - Caramel / Crystal 40L 5.6%
0.15 lb Corn Sugar - Dextrose - (late addition)

Mash in a 151F with a thickness of 1.75qt/lb

 

[robopp]

That's like a 90% attenuation. Are you sure your hydrometer is accurate? (Check with distilled water). Also, is it the taste you're not satisfied with or just the number.


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Not using distilled water but basic tap water reads around 1.000, which I assumed was 'good enough'?

I guess I started getting frustrated last night while drinking a glass of Avery's Maharaja followed by one of my 90-minute clones. The clone was so dry compared to the Maharaja.

 

[robopp]

Have you calibrated your thermometer. It may be reading high? You may think your mashing at 152 and it is really at 149.

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I have not calibrated my thermometer. I'll do this now. Would a temp difference between 152 and 149 affect attenuation that much?

 

[BackAlley]

Not using distilled water but basic tap water reads around 1.000, which I assumed was 'good enough'?

I guess I started getting frustrated last night while drinking a glass of Avery's Maharaja followed by one of my 90-minute clones. The clone was so dry compared to the Maharaja.

According to the CYBI clone recipe, there's 1.5lb of DME in a 5g recipe. Not sure if that would contribute to a higher FG. Also, the clone recipe lists 1.010-1.012 as the target FG


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[Beernik]

Could over pitching be a problem with 1 gallon batches? What is your yeast?

Over pitching can lead to over attenuation and thin beer.

 

[tagz]

Do you check your mash temp at the end of the mash? With smaller batch sizes, you can have trouble maintaining temp because of the lower thermal mass. You can also try to measure the difference between the temp in the center and the edge of the container. I was having a similar issue. I found that if I preheated the MT really well and then stirred like crazy at dough-in, I got more consistent temps. I tend to over shoot my strike temp so that I can stir it down to the right mash temp. For example, I might use a strike temp of 154 so I can stir everything up and still hit 152.

 

[robopp]

Could over pitching be a problem with 1 gallon batches? What is your yeast?

Over pitching can lead to over attenuation and thin beer.

I use mrmalty for my pitching rate. I've only used dry yeast and mainly just S-05 and S-04. For a OG of 1.080, I pitch approximately 1/3 of a 11.5g packet.

 

[robopp]

Do you check your mash temp at the end of the mash? With smaller batch sizes, you can have trouble maintaining temp because of the lower thermal mass. You can also try to measure the difference between the temp in the center and the edge of the container. I was having a similar issue. I found that if I preheated the MT really well and then stirred like crazy at dough-in, I got more consistent temps. I tend to over shoot my strike temp so that I can stir it down to the right mash temp. For example, I might use a strike temp of 154 so I can stir everything up and still hit 152.

I have checked the temperatures at the end of the mash and usually it's only off by a couple degrees. Could this be the problem? Is there a big difference between 152F and 149F?

I've actually started doing exactly what you're recommending. I start with a mash temperature that's +2 degrees from my target, close the cooler and wait 5 minutes. Then stir again and check the temperatures, usually targeting +1 degree of my target. I haven't been able to check the final gravities of these beers but I'm hoping the FG is closer to my target.

Thanks for the help!

 

[balazs]

I have not calibrated my thermometer. I'll do this now. Would a temp difference between 152 and 149 affect attenuation that much?

I am not sure if this is your issue but it is one probability to look into. If your thermometer is way off it might have something to do with it. Rule out all possibilities by checking the easy one's first.

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[MindenMan]

What is your sparge temperature/volume? A grain bill that size should be making a 1.080 O.G.

 

[robopp]

I am not sure if this is your issue but it is one probability to look into. If your thermometer is way off it might have something to do with it. Rule out all possibilities by checking the easy one's first.

Sent from my SPH-L720 using Home Brew mobile app

I calibrated the thermometer using another thermometer and they read the exact same temperature, which I think rules out the thermometer.

I think I've figured out what's wrong. I just finished brewing a Heady Topper Clone and I was aiming for a strike temp of 151 holding it for 90 minutes. I decided to check the temp after 60 minutes and it was down to 146! I've never preheated my mash tun and I'm wondering if this is the root cause or at least a big contributing factor? Also, in the future, I'll be sure to better insulate the cooler since I could feel a noticeable warmth on the outside of the lid.

Thanks for all the help guys!

 

[duboman]

Your strike temp should be 5-10 degrees higher than your desired mash temp as the temp of the cooler and the temp of the grain will drop the water temp that same 5-10 degrees.

If you are using a strike temp that is too close to the desired mash temp you will ultimately mash lower than desired creating a more fermentable wort, higher attenuation and lower FG readings.

Also, calibrating one thermometer against another. Is a shot in the dark unless you're using a certified lab thermometer as the control


Sent from the Commune

 

[robopp]

Your strike temp should be 5-10 degrees higher than your desired mash temp as the temp of the cooler and the temp of the grain will drop the water temp that same 5-10 degrees.

If you are using a strike temp that is too close to the desired mash temp you will ultimately mash lower than desired creating a more fermentable wort, higher attenuation and lower FG readings.

Also, calibrating one thermometer against another. Is a shot in the dark unless you're using a certified lab thermometer as the control


Sent from the Commune

Sorry, you're right. I was mixing up terminology. My strike temp was actually 170F and the mash settled down to the desired 152F. After hitting my temp, I waited 5 minutes then reopened the mash tun to check the temperature again. It was a little low so I added some boiling water to bring it back up to 152F.

I agree, but what are the odds that both thermometers are off? If it's worth anything, and I don't think it is, the second thermometer was a analog alcohol thermometer.

 

[tsl346]

You might try mashing a little thicker, around 1-1.25qts/lb. Palmer discusses that mash thickness will affect the fermentability of the wort. A thinner mash will make a more fermentable wort and the thicker mash will make a less fermentable wort. Not sure if it would make this extreme of a difference but your mash does seem thin to me.

 

[tagz]

I just finished brewing a Heady Topper Clone and I was aiming for a strike temp of 151 holding it for 90 minutes. I decided to check the temp after 60 minutes and it was down to 146!
Thanks for all the help guys!

There it is! That low a mash temp will definitely result in a low FG. I remember having a similar problem when I started doing partial mashes in a 2 gallon cooler. When you do larger batches the volume tends to hold the temp much better.

So, you can try preheating. Fill the cooler to the top with very hot tap water and let it sit while you are getting set up. I also bought some bubble insulation at the hardware store at one point and made a jacket for the cooler.

If you can find a way to hold your temps better, you'll solve your problem!