[fredthecat]

1. at start of transfer from kettle to carboy i filled the test tube with wort. i use a racking tube. i allow what i perceive to be the racking tube "pull"(?) water to go into a container then immediately poured it into the test tube. when thats full i immediately move it to the carboy and let it go.

2. after carboy was full i added hydrometre to test tube. gravity was 1.044 after temp correction. expected OG was to be 1.049. 100% DME was used along with 250g of a steeping grain in cold water (i did not expect it to contribute gravity). water was carefully measured so estimate should be counted upon.

3. disappointed, as ive had been undershooting my OG a fair bit and never overshooting it. i took a sample of the trubby remaining wort (i used a hop spider, so no big solids) and tested its gravity in the test tube with the same hydrometre. this time it read 1.051.


would significant trub affect the gravity reading? is it likely that the first 1.044 reading had some water mixed in with it, lowering it?

[ynotbrusum]

It sounds like you are watering down the test wort, but not by a lot.  Even so, the smaller overall sample will result in a wider effect.  The bigger and longer the tubing, the more volume, of course.  As to wort reading, I have always allowed the sample to settle out for the reading with the hydrometer to avoid the solids from affecting the reading.  Maybe the effect will be minimal, but I don't know how much that would be and a few points are always a possibility, depending on how thick the particulate is.

I know this doesn't fully answer your question and is based on my own personal experience, but it is what I think happened here.  Personally, I don't sweat gravity readings anymore (but I brew very low ABV beers for the most part.)

[Richard]

I agree with the previous statement. If your sample is 8 oz in volume then 0.8 oz of water would lower the gravity from 1.049 to 1.044. That is 4.8 tsp (24 ml), which is a substantial amount.

Trub can have a small effect on the reading, but usually not much. Let the sample settle in the hydrometer tube. If the trub is much denser than the wort it will settle out fast. Once it settles below the level where the float is then it can't affect the reading anymore. If it takes a long time to settle then the density of the trub is not much different than the density of the wort so it can't have much affect on the reading.

[fredthecat]

It sounds like you are watering down the test wort, but not by a lot.  Even so, the smaller overall sample will result in a wider effect.  The bigger and longer the tubing, the more volume, of course.  As to wort reading, I have always allowed the sample to settle out for the reading with the hydrometer to avoid the solids from affecting the reading.  Maybe the effect will be minimal, but I don't know how much that would be and a few points are always a possibility, depending on how thick the particulate is.

I know this doesn't fully answer your question and is based on my own personal experience, but it is what I think happened here.  Personally, I don't sweat gravity readings anymore (but I brew very low ABV beers for the most part.)

appreciated. i think it will be a matter of enough people giving their 2 cents.

I agree with the previous statement. If your sample is 8 oz in volume then 0.8 oz of water would lower the gravity from 1.049 to 1.044. That is 4.8 tsp (24 ml), which is a substantial amount.

Trub can have a small effect on the reading, but usually not much. Let the sample settle in the hydrometer tube. If the trub is much denser than the wort it will settle out fast. Once it settles below the level where the float is then it can't affect the reading anymore. If it takes a long time to settle then the density of the trub is not much different than the density of the wort so it can't have much affect on the reading.

yup, sample liquid was about 180ml or 6.5oz i believe.
good explanation of the trub. i am leaning towards it being accurate as it was full of very soft and fine particles (and also i want that to be the right one)

[RC]

You can rule out trub. Being a solid, it doesn't contribute to a solution's density and so won't affect a gravity reading. If anyone needs convincing: take a hydrometer reading, then put marbles or pebbles in the bottom of the tube, then take another reading. The volumes will differ but the gravities should be the same.

Yes, it's possible the first sample was inadvertently watered down. Another possibility is that during the time it took to rack the beer from kettle to carboy--and assuming the bottom of the racking cane was near the bottom of the kettle--the wort stratified according to density, with the more dense wort at the bottom. By the time of that second reading, you were simply measuring denser wort. For this exact reason, I always capture my OG wort sample during the final minute of the boil, when the wort is still being well mixed.

 

[Richard]

You can rule out trub. Being a solid, it doesn't contribute to a solution's density and so won't affect a gravity reading. If anyone needs convincing: take a hydrometer reading, then put marbles or pebbles in the bottom of the tube, then take another reading. The volumes will differ but the gravities should be the same.

That is an over-simplification. The principle of bouyancy is that the bouyant force is equal to the weight of the material displaced. If you have a very dense solid that sinks to the bottom, as you proposed, then it is not displaced and doesn't affect the reading. However, if you have particles in suspension that are displaced by the float then they will affect the reading. As I said, though, if they remain in suspension very long then they are not much different in density than the liquid so it won't matter much.

A couple of years ago there was a discussion of whether yeast in suspension would affect a hydrometer reading. Denny asked "If you fill a swimimng pool with poodles does the water get more dense?" Here was my response to that:
https://www.homebrewersassociation.org/forum/index.php?topic=31145.msg404993#msg404993

[mainebrewer]

Since the wort was made with 100% DME, if the volume of water was correct, then the SG can be determined by the number of pounds of DME and the volume of water added.
If the full volume wasn't boiled together, then stratification is the likely reason why the OG measurement was lower than expected.

[fredthecat]

Since the wort was made with 100% DME, if the volume of water was correct, then the SG can be determined by the number of pounds of DME and the volume of water added.
If the full volume wasn't boiled together, then stratification is the likely reason why the OG measurement was lower than expected.

that does make sense. it was breiss DME, so it should be pretty consistent. full volume was boiled tho.

my LHBS has an off-brand LME and it gives me lower than expected for brand name LME gravity points i find, but ive sort of dialed it in on my brewing software.

[denny]

Since the wort was made with 100% DME, if the volume of water was correct, then the SG can be determined by the number of pounds of DME and the volume of water added.
If the full volume wasn't boiled together, then stratification is the likely reason why the OG measurement was lower than expected.

that does make sense. it was breiss DME, so it should be pretty consistent. full volume was boiled tho.

my LHBS has an off-brand LME and it gives me lower than expected for brand name LME gravity points i find, but ive sort of dialed it in on my brewing software.

With extract batches it seems like its more accurate to calculate the gravity than measure it