Low OG

[Vladimir Kim]

Hello. Relatively new to all-grain brewing. I have a Clawhammer 120V system and I typically brew two gallon batches. My issue is that I always have very wild swings in terms of OG and I can't figure out why. Today I brewed two batches with relatively similar grists of 2-row, oats, and carafoam. I have a mill at home that I use with a drill at low speeds and I crush twice with credit card sized gap. I use Brewfather for calculations and my pre-boil gravity is usually on target, as well as pH. My mash is at 152F for 60 minutes followed by mash out at 170F for 10 minutes. I measured pre-boil SG at the end of my mash and they were both on target at 1.051 and 1.055 (pH 5.4 for both). After a 60 minute boil, I chilled and transferred to fermentors. The first had a FG of 1.058 and the second of 1.060. Not sure why I'm not hitting the required SGs of 1.070 and 1.073. I use the same refractometer for the readings and my pH meter tells me that the samples are at ~60F. I even compared to a floating hydrometer and had same readings. Beers turn our great but I would like to get my numbers in line so that I can re-make these beers in the future with same results. Any advice appreciated, thanks.

 

[McMullan]

Have you measured your boil off rate? Your expected might be too high. Seems high to me.

 

[IslandLizard]

Welcome to our forums!

I looks like your boil-off is not sufficient.
You're not topping up volume at the end of the boil, are you?

The mash extracts an amount of sugars, in a certain volume. Boil-off then condenses your wort, lowering the volume while raising the gravity.
Think of gravity and volume as a rubber band, longer (higher volume) but thinner (lower gravity), or shorter (lower volume) but thicker (higher gravity).

 

[hotbeer]

You need to look at the volume of wort that you had at the end of each boil and compare it to what the recipe software you used said it should be.

If you had more volume of wort than was expected, then your wort will likely be a lower SG. So either boil longer or use less water. There should be a correction for that in your software. Most all beer recipe software lets you tailor the various efficiencies and other things to what you get consistently in your own processes.

At least the two examples you give are within 2 points of each other. So at least your procedures are giving you consistent enough results to allow you to make corrections in the software for your efficiencies.

If your evaporation rate is correct, then perhaps you just need to use more malts unless you can figure out how to improve your extraction rate during the mash.

Efficiency isn't a competition or grade for your beer making. It is just what your processes give you. When you know your efficiencies you can tailor a recipe made by another to give you the same OG, FG and other things so you get a beer that is more closely to what they made.

However if your mash efficiency is below 60%, you might want to at least get that up to a C.

I chilled and transferred to fermentors. The first had a FG of 1.058 and the second of 1.060.

OG.

FG is final gravity at the end of fermentation.

 

[Vladimir Kim]

Have you measured your boil off rate? Your expected might be too high. Seems high to me.

I looks like your boil-off is not sufficient.
You're not topping up volume at the end of the boil, are you?

If you had more volume of wort than was expected, then your wort will likely be a lower SG. So either boil longer or use less water. There should be a correction for that in your software. Most all beer recipe software lets you tailor the various efficiencies and other things to what you get consistently in your own processes.

I will have to look into this. I have the software currently showing 0.75 gal/hr from the profile for the system. The kettle came etched with markings but since I use 1-gallon water jugs I noticed that the measurements are off. I'll have to mark the kettle correctly and see what the boil off rate is. If I use plain water as a test, will it be the same as with wort?

At least the two examples you give are within 2 points of each other. So at least your procedures are giving you consistent enough results to allow you to make corrections in the software for your efficiencies.

They're different recipes. One of them I have brewed before and it had an OG of 1.059. This time that same one was 1.060. I think my mash efficiency has been around 70% consistently which is what I put into the software. As you and others have pointed out I will have to check the boil rate and I'll report back to see if that made a difference. My main goal as you said is to be able to recreate other people's recipes and this is the last step hopefully before I fully understand my system.

OG.

FG is final gravity at the end of fermentation.

Yes, my bad. I did mean to write OG.

Thank you all for the feedback.

 

[Vladimir Kim]

I measured the boil-off rate three times and got an average of about 0.55 gal/hr. In addition, I made the necessary adjustments to the equipment profile in my software based on measured values and the numbers are now all correct. In fact, my efficiency is actually about 72-73%, more than the 70% I estimated before. Happy days, thanks all again.

 

[IslandLizard]

The kettle came etched with markings but since I use 1-gallon water jugs I noticed that the measurements are off. I'll have to mark the kettle correctly and see what the boil off rate is.

Volume marks in most kettles are often a (very) rough guide and hard to read. I wouldn't bother etching in new ones, just use a measuring stick or dowel you've calibrated to the actual volumes, or a ruler.

In my main kettle every inch and a half of water/wort height is a gallon. But the kettle is also 14 inches wide, and 1/4" is about the most precise "reading" I can get, thus reflecting 1.3 pints, give or take.

If I use plain water as a test, will it be the same as with wort?

Yeah, it's the same, you're evaporating water.

I measured the boil-off rate three times and got an average of about 0.55 gal/hr. In addition, I made the necessary adjustments to the equipment profile in my software based on measured values and the numbers are now all correct.

Alright!

In fact, my efficiency is actually about 72-73%, more than the 70% I estimated before. Happy days, thanks all again.

You're getting there!
There are many places in a brew session where a brewer can improve their efficiency.
But since you're doing relatively small batches, the cost savings or extra yield are generally not that big either.