Old grains and conversion efficiency

[HopMantis Brewing Co]

So I have a few all grain kits I ordered from NB. Got a great deal on some IPA kits even though I usually just slap my own recipes together. So I brewed one of those kits yesterday and I had them since November. They were pre-crushed as I don't have my own mill. They were kept cold (38F) but not frozen. I tasted the grains before I brewed and tasted fine. My efficiency was horrible yesterday - about 58%. Does anyone know if the diastatic power decreases the longer the malt is exposed after being crushed? I mean I will still get beer but I was expecting somewhere around 72% and a 1.072 OG. I got 1.052 OG. I've never had this problem before. I've also never ordered recipe kits from NB. I usually buy local and only pre-crush the day before brewing.
Cheers ~

 

[HighVoltageMan!]

I don't believe that the grain would lose much DP over time unless it was moldy or something really bad like that, the malt would most likely become stale and lose a lot of flavor more than anything.

Bad conversion efficiency can have a number of sources, the enzymes can become denatured by both temperature being too high and pH too low. But that I think would be pretty obvious at the time you were mashing. Low conversion could be because the pH of the mash was off. Beta enzymes prefer higher pH and alpha works better at lower pH's. Get that wrong and I have seen effeciency drop.

To me there is reason for such low conversion efficiency, but I don't believe it's because the the grain was 6 months old or so.

 

[Starter Hops]

I did a 9-month old, crushed, NB recipe kit 6 weeks ago and yeah I got like 52-53% efficiency. The kit was a hand-me-down via third party. I didn't even know if the bags of hops were ever refrigerated, sure smelled like they weren't. I hit my OG, being a pale ale that wasn't hard to do, I just boiled less water presuming a loss of unknown magnitude.

 

[Mark D Pirate]

Ive used grain that was over 2 years old and uncracked .
i made my usual pale ale with it using 50 % fresh malts and hit every target within a point or so .
Do you have the capacity to do double batches ? using an old one and a fresh one together should work just fine