Very low final gravity. Why?

[BeerBanana]

Hi Everyone. I just brewed my second batch of beer. (All grain, I'm diving head first into this crazy but awesome hobby).

I did a gravity reading the other day before bottling. It came in much lower than expected, at 1.002 (it should be around 1.010). Just wondering why this could have happened? My home brew store reckons contamination but I thought I was being pretty meticulous about cleaning (although I did use a new fermenter for the first time).

I tried some of the sample vial, it tastes very dry and bitter, probably because there's no sugar left, but it didn't taste terrible.

Any thoughts? Thanks in advance.

 

[Redlantern]

Assuming it was contamination, it is time to insert the general disclaimer - there is a difference between clean and sanitized.

All parts that touch the wort and beer after the boil must be sanitized with a sanitizing cleaner or other process (i.e. boiling or autoclave)

Transfer lines, fermenter, rubber stoppers, spoons, the outside of the yeast package - anything that comes in contact with the beer needs not only to be washed, but sanitized after washing. Clean is just the start.

Idophor or Starsan are two examples of solutions used to sanitize. Even your hands are suspect.

Granted we all know this - but do you think there is pay part of the process where that was missed? Process review might reveal something that did not happen even though you planned for it. We have all been there - a missed step - a forgotten something or other. We may have gotten away with a dozen times, but occasionally we get caught...

 

[Dmoney1911]

It could be a contamination, but there's a more likely chance it is not. If it has only been fermenting a short time, like a couple weeks, any wild yeasts/bacteria probably wouldn't take hold that fast. People wait months for the stuff to do their thing when they purposely pitch wild yeast or bacteria in high quantities.

There could be a number of reasons why the gravity is that low. Different strains of yeast act differently, and sometimes the same strain will have different results in different conditions. Which yeast strain did you use, and how much did you pitch? High pitch rates, yeast nutrient addition, aeration, and possibly high ferment temps can all make the yeast more active.

Another possibility is that in doing your all grain mash, your mash temp was on the low side (around 145-148F). How did you do your mash step? Mashing at that lower temperature will create a low percentage of unfermentable sugars, and the yeast will take down almost everything.

 

[Dmoney1911]

Also, if the gravity is that low and is infected.....you will know. It will taste either sour or funky

 

[soccerdad]

What yeast did you use?

Did you add sugar or honey at the end of the boil?

 

[BeerBanana]

Thanks heaps for the quick replies!

To answer:

- I did use starsan, on pretty much everything I can think of. Only possible contamination sources would be the glass flask that I used to make the starter (although I boiled that on the stove so would have thought that would be OK); or a drop of sweat that went into the wort (it was hot).
- Fermentation temps did get kind of high. I just did another post about a keezer build... It's the middle of summer here and the wort got up to 28 C some days but that was after about 5 days of fermentation.
- Yeast was Wyeast American Ale 1056, made into a starter and decanted. No nutrient.
- Aerated by whisking the wort after it had cooled. Sanitised the whisk. Made lots of foam.
- Mash was done in a robobrew around 65 - 70F, I think that was OK.

Thanks again
Cheers

 

[glugglug]

What was your og? Could your hydrometer be off?

 

[whovous]

Let's rule out the other possibility. You say you are brand new to the hobby. How did you measure your final gravity? Is there any chance you measured wrong? Has anyone else confirmed your measurement?

 

[BeerBanana]

I measured the gravity via a sample vial and hydrometer. I think I got the reading right, it's possible I got it wrong, but I feel like another explanation is more likely.

 

[Dmoney1911]

It could just be one of those things, if there wasn't any error with your equipment (thermometer calibration, hydrometer). You can use recipe calculators and not always hit the expected final gravity, which is why actual gravity readings are important.

I would try to keep the fermentation temp a little lower, around 16-20C, because that will also limit some off-flavor compounds. It's possible you pitched more yeast than you needed, depending on what your OG was, but it's better to be on the side of slightly overpitching than underpitching. making a normal starter from 1 liquid yeast pack probably wasn't too much. Back to what I said earlier, aeration will increase yeast growth and activity, but is definitely necessary to do so.

 

[catdaddy66]

Lower mash temps (148-150) will give you more fermentable sugars that will bring your FG down a lot. Also, the type of yeast used matters, as some are voracious sugar munchers (Belle Saison ftw!). Those may be more common reasons vs contamination or infection.

 

[rkzi]

What was the OG, how long did you mash, how did you sparge and did you do a mash out? In case you didn't do mash out, was there a delay between the end of mash and start of boil?

 

[dipsomanic]

My guess is that your hydrometer isn't calibrated Does your hydrometer read 1.000 in room temperature water?

 

[Redlantern]

In addition to the hydrometer calibration, at what temperature was the beer when you tested the gravity?

 

[Dmoney1911]

1.002 is definitely possible to achieve. Could just be a very high attenuation, especially if it tasted very dry.