OG topic

I am wondering what could cause your original gravity be off, high or low?

I haven't had this problem yet but it's always good information to know. Just in general what are some of the things to look out for that could cause problems in this area?


Thanks for any responses.

If you're not doing all grain, and just doing a pure extract beer the only thing that should throw it off would be the temperature that you took your reading at.


Other than that I think it comes down to efficiency and I think if your water is really mineral heavy that can throw it off as well.

funkapottomous said:

If you're not doing all grain, and just doing a pure extract beer the only thing that should throw it off would be the temperature that you took your reading at.

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Or, having a volume different from what you expected, say from boiling losses, measurement errors, etc.

broadbill said:

Or, having a volume different from what you expected, say from boiling losses, measurement errors, etc.

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I knew I was forgetting something!

One thing I've noticed when topping off my extract batches is that if I haven't mixed it up well, the OG might be off, because it's not evenly mixed and most of the wort is at the bottom, while it's mostly just water at the top where I'm measuring it.

This is not really an issue unless your brewing all grain or partial mash. In extract brewing you are stuck with what ever the processing plant packed and shipped that day. I have had extract batches that come out a little high and some come out a little low, but in the end they end up making great beer. If you are concerned about your G readings being off, one thing to check is water volume. I was 2 batches into brewing and my numbers were slightly off and I discovered that those nifty little volume marks on my fermenting bucket were WRONG!!! I had an actual volume of a bit more than 4.5 gallons. I weighed out 5 gallons of water and used that water level to mark my bucket and made a stick to measure new buckets in the future.

akervin said:

I am wondering what could cause your original gravity be off, high or low?

I haven't had this problem yet but it's always good information to know. Just in general what are some of the things to look out for that could cause problems in this area?

Thanks for any responses.

Click to expand...

Well since the SG is a measure of the density of the liquid. A number of things can throw it off. Most hydrometers are supposed to read at 60 deg. F. So if the temp is warmer than 60 when the OG is taken you will subtract .003 from the reading for every 10 degrees warmer because the liquid will be less dense. Same applies if the temp is 10 degrees cooler only you add .003. Not having enough water will throw it off because malt extract is denser than water.

If your measurements for water are off, that can affect the OG.

Specific gravity is measuring the density of your wort compared to that of just plain water, and that density measurement goes up when there is more "stuff" in the solution.

If you keep in mind that its just a ratio of fermentables (and some non-fermentables) to water, then you can adjust it when it's too high or too low. You can add water to it (reducing the ratio) or you can either A) add more fermentables (such as malt extract) or B) remove some water by boiling it off, both of which will increase the gravity.

--Jimbot

Those are some great points. I appreciate the responses .

I notice I read "boil off" in there a few times. Should you try and maintain a level of wort in your kettle while boiling by adding small amounts of water at a time or just add it all in the end once you cool the wort?

akervin said:

Should you try and maintain a level of wort in your kettle while boiling by adding small amounts of water at a time or just add it all in the end once you cool the wort?

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I'd say no, don't add water while boiling. That will make it harder to keep up a good boil.

IF you are boiling the entire batch (5 gals let's say), and if you know how much water you normally boil off in 1 hour, then you can plan ahead to start with enough water so when you are done you are right at your target (5 gal).

IF you are boiling part of the batch, then you can just add in the top-off water at the end... with the added bonus that it will help cool down the wort faster, so you can pitch yeast sooner!

--Jimbot