Can suspended hops/yeast affect gravity readings?

[ghank15]

Yesterday I took a sample of a lager I brewed a week ago. It read 1.020.

After I take my hydro samples I always put it in a glass and refrigerate it so I can drink it.

Today, I opened the fridge and saw that there was a good quarter-half inch of yeast and hop gunk at the bottom of the glass. So I took another gravity reading, and, after adjusting for temperature, I was at 1.013.

So I was curious about how much the amount of suspended hops and yeast really impact gravity readings. The beer was a lager, so I know it didn't ferment 6 points at 43 degrees in 24 hours, so I'm guessing the 1.013 is much more accurate than the 1.020 I had yesterday.

Any thoughts would be greatly appreciated, as about 75% of my beers have finished between 1.018 and 1.020. However, this is the first time I have ever allowed the gunk to fall out of suspension before taking my final gravity reading. Being that I have brewed almost all ales, I'm taking my readings in similar conditions to that of yesterday. I'm wondering if some of those 1.020 beers were in fact slightly lower.

For the record, my hydrometer is accurate. I get 1.001 with tap water and 1.000 with distilled water at 60 degrees.

 

[daksin]

No, only truly dissolved substances like sugar and alcohol will affect the density of the solution. Suspended particulates won't, and therefor won't affect the gravity reading.

A bigger factor might be dissolved CO2 coming out of solution and sticking to your hydrometer, raising it up. By letting your sample settle, more CO2 may have come out of solution before you added your hydrometer, so that the effect was less noticeable.

Also: are you correcting for temperature? Hydrometers are calibrated for 60F usually, so you will need to use an online calculator. Your sample probably warmed up while you letting things settle.

 

[ghank15]

Yes, I corrected for temperature.

So which reading was the more accurate one? The 1.020 or the 1.013?

Is it advisable to let everything settle when taking a gravity ring when there is visible C02 in the beer?

 

[wailingguitar]

A bigger factor might be dissolved CO2 coming out of solution and sticking to your hydrometer, raising it up. By letting your sample settle, more CO2 may have come out of solution before you added your hydrometer, so that the effect was less noticeable.

.

FYI, disolved CO2 will give a false low, not false high SG

 

[ghank15]

FYI, disolved CO2 will give a false low, not false high SG

Thanks. I guess this means that 1.013 is a more accurate number. In the future, I should probably wait until the stuff settles before I take a reading.

This also makes me feel much better, because I mashed this batch at 147.5 and used only .5 pounds of crystal and .5 pounds of caramunich as my specialty grains. Every other grain was fermentable, and at this temp, I should have extracted more fermentable sugars than unfermentable sugars. I have almost gotten used to my extract batches that finished at 1.020, and I had hoped that my AG batch would be better.

Thanks for the info.