5 gal batch had 1/2oz hallertauer @ 20 min and 1/2 oz hallertauer @ 10 min left in boil. The 10 gal batch was 1 oz hallertauer @ 20 min and 1 oz hallertauer @ 10 min. Note: the 10 gal batch was fermented in 2 seperate carboys.
Sorry if this throwing a lot at you, but I'm trying to give you some leads to go on as to what caused the change.
Were the FG's the same? a lower FG would be less malt flavor in by comparison, more pronounced hop presence.
Did you up your starter for the increase in wort? underpitched yeast could affect the flavor. A low pitch rate can lead to:
* Excess levels of diacetyl (buttery)
* Increase in higher/fusel alcohol formation (hotness)
* Increase in ester formation (fruity)
* Increase in volatile sulfur compounds
* High terminal gravities
* Stuck fermentations
* Increased risk of infection
Do you use starsan or bleach? Bleach will give you a chemically flavor that may taste bitter. Perhaps one of the fermenters you used wasn't totally scrubbed of bleach.
Also, From a different thread:
one other thing to consider, your evaporation rate might change during the boil, if your brew kettle gets much wider in diameter. more surface area = more potential evaporation.
Basically, if you're using different width kettles, your evap rate will change. Using the same kettle, your taking longer to get 10 g to a boil and likely losing more water there preboil.
The only other thing I could think of is trub. Do you transfer your wort trub and all? or do you filter it out? You may have gotten more of it in the 10g batch than the 5g batch.
There's a ton of variables that come in to play. Simple math says doubling the batch size means double the recipe, but from what I've heard, in most cases - when you scale your recipe up in proportion to the increase in volume, something changes. The chemical reactions happening in the new system are different than the chemical reactions in the old system and will likely affect the flavor.
If all you can think of that changed is your fermentation method (split fermentation), try finding a 10 g bucket to ferment in. Perhaps fermenting all in one place was the difference.
Or, for your next batch using ten gallons, instead of doubling the hops, increase it by less than that!
Worst case scenario for your current batch, you let it sit for a few months and let the bitterness mellow out.