Low OG - suggestions why?

[manticle]

And still a better man if it's 6.5kg (being a pedant, or is that peasant?)
Very rough rule of thumb I use to double check recipes is 1kg grain (22l batches) gives 10 points of gravity for up to 5kg or so and then drops fairly rapidly. And yes I know it's very rough and is affected by loads of variables, but it's only a sense check. So sIngle mash of 6.5kg on my system should get me an OG of around 1.065

I wasn't including the spec (notice I said base?)
For a moment, I thought my year ten maths had left me.

That is rather a lot of cara. Sorry to ask but was the base milled or unmilled during its year long storage?
And how much base grain would you use for 20 L of 4-5% beer?

 

[Blind Dog]

I'll get my coat...

 

[brewermp]

Man never knew that gravity was affected by wort temp.

 

[nolube]

I use 84% efficiency, about 4kg will give me a 5% beer.

The maris otter was stored unmilled, and milled just before brewing. The mill had to be adjusted to get a proper crack because it had shrunk a lot.

 

[manticle]

I reckon you typed something in wrong. I haven't run the calcs but I'm failing to see how an extra kilo of base and a kilo of spec could net you 30 odd gravity points.

Run through the thread and see if any of the suggestions explain your result.

Off the top of my head, the most logical explanations are:

1. Error in data entry (in brew software) - this is my guess.
2. Error in measuring equipment (eg. measuring hot wort sample, uncalibrated refractometer)
3. Decreased efficiency due to increased malt bill (as per Blind Dog)
4. Not enough boiloff - you should have had way more volume than expected if this were the case.
5. Stratification of wort (relevant if sparging, less so if full volume BIAB)

In order to nut out where the problem is, you really need to isolate at which point gravity came out lower than expected. Is it first runnings? Total runnings/preboil? Post Boil? Cooled wort?

I think if the malt was in good condition to begin with and was stored well then 12 months shouldn't see anywhere near a drop like that.

 

[nolube]

Interesting mate, thanks for your reply... After considering your points, I guess we'll never know as I'm pretty sure everything was in order.. Will try the brew again someday soon with some fresh grains and see how I go.