Problems with SG readings

[kbuzz]

I got a refractometer for Christmas. Was so excited to use it that I calibrated with a bit of bottled water and used it on my first brew day the next day - 12/26. Brewed an Imperial India Brown Ale AG recipe...projected OG was 1.073 and ended up at about 1.076 using the refractometer. Had a pretty sizable yeast starter going for a couple days prior to brewing. On 1/6, I threw in the dry-hops, just assuming it was done fermenting. Took a gravity reading about 6 days ago - 1.040...crap...took another today - 1.040. I chalked it up to the cold basement - temps hang out @ 62 or so. Must have underattenuated despite me using a starter...thought that temps got too cold and that was that. Fermentation just petered out.

Then on a whim, I decided to check the reading with my old hydrometer - low and behold, I got a reading of 1.019...still not great, but better than 1.040. So the next step was to check calibration - both the refractometer and hydrometer gave me a 1.00 reading (after temp conversion for the hydro) for a bit of tap water. What is going on here??? Was my original gravity reading bad too?? No way I missed my targeted OG by .02 - that would be crazy - I've never missed that bad. I'm drinking a glass right now and it's giving me a nice little buzz, so I don't think the ABV is only 5%.

What could be wrong here? Am I an idiot?

 

[mvcorliss]

A refractometer is designed to measure sugar in water. When you add alcohol to the mix your reading becomes very inaccurate. There are calculations to convert the post fermentation reading but most people feel they are only ballpark at best.

 

[Yooper]

A refractometer is designed to measure sugar in water. When you add alcohol to the mix your reading becomes very inaccurate. There are calculations to convert the post fermentation reading but most people feel they are only ballpark at best.

Correct. Grab a hydrometer and see what the FG is once fermentation has begun. there are some calculators that can do the compensation, but they aren't all that accurate either.

 

[kbuzz]

Correct. Grab a hydrometer and see what the FG is once fermentation has begun. there are some calculators that can do the compensation, but they aren't all that accurate either.

So is there no real advantage to the refractometer post-fermentation?

In other words, should I just use it on brew day when sparging/boiling, etc...then continue to use a hydro sample for FG readings?

 

[david_42]

Right. Where a refractometer shines is during the sparge process. It's a royal pain to translate a FG reading, so just use you hydrometer.

 

[Yooper]

So is there no real advantage to the refractometer post-fermentation?

In other words, should I just use it on brew day when sparging/boiling, etc...then continue to use a hydro sample for FG readings?

Well, yes. Unless you just want to see if the beer is still fermenting, and don't really care about FG. What I mean is, if the refractomber shows 11 brix today, and 10 brix tomorrow, the it's still fermenting so a great deal of accuracy isn't important. But if you think it's done, a hydrometer is usually the best tool for deciding the next step.

 

[kbuzz]

Well, yes. Unless you just want to see if the beer is still fermenting, and don't really care about FG. What I mean is, if the refractomber shows 11 brix today, and 10 brix tomorrow, the it's still fermenting so a great deal of accuracy isn't important. But if you think it's done, a hydrometer is usually the best tool for deciding the next step.

A-ha...gotcha...perfect

Thanks all!!

 

[RM-MN]

From what I see from not having a refractometer is that it can save a lot of time during the mash/sparge as you don't have to wait for a large quantity of wort to cool down so you can use your hydrometer. Once you have alcohol you have cooler wort/beer so taking a hydrometer reading is pretty easy and accurate. One doesn't replace the other, they compliment each other.

 

[kbuzz]

Yeah, makes sense now.

I just hate taking such large samples for hydrometer readings. Not that I don't drink them, but I just feel like I'm wasting beer.