A couple of low gravities...

[gerard weyns]

I have brewed 6 batches now on my 3-vessel electric herms rig and I am having a blast. 4 out of the 6 I have either hit my original gravity or gotten very close, but two of the batches came out much lower than what the recipe called for. The first was a whit that came out at 1.039 when it needed to be 1.048. The second was a blonde ale that came out at 1.040 and needed to be 1.051. I have been using a refractometer to check gravity during the brew process and then both my refractometer and hydrometer to record original gravity after chilling, so I am positive I am getting accurate readings. There are a few factors that I think may have contributed: I picked up and milled the grain for the whit at a different brew shop than I normally go to. All of the grain had been crushed or split, but was not as finely milled as normal. The blonde ale called for a pound of table sugar that was listed with the mash ingredients, so I added it to the mash rather than the boil. After doing some reading the next day I learned that sugar is typically added at the very end of the boil... my bad. The blonde ale recipe also claimed an 87% mash efficiency, and although I haven't accurately calculated my efficiency yet I would say it is somewhere around 70-75%. Anyways I followed the recipe exactly and did not scale up for efficiency. The recipe for the whit did not specify the efficiency of their rig. I am still very new to brewing and would appreciate all the input you can give. What is most likely the culprit here??

 

[Upthewazzu]

I always have trouble hitting my targets on beers that contain a fair amount of wheat. Not sure if you recipe's had any or not.

Also, Go Cougs!

 

[Rob2010SS]

Efficiency can play a huge part of this. If a recipe is built for 85% efficiency and you're only getting 75% efficiency, it can be a drastic difference. It could very well be the culprit in this scenario.

Adding the sugar to the mash instead of the boil on the blonde could be part of the issue for that one, in combination with the efficiency difference.

How you sparge could also play a role. If you're not sparging enough or correctly, it could lead to this. However, I'm more inclined to lean towards efficiency as the culprit as you said you've hit your gravities before but these were set at 87% efficiency. I have the cooler setup and my efficiency is 75%. I know people can and are hitting mid or high 80's on their efficiency but I would guess that's your culprit.

If you go back to that LHBS, you could run them through the mill twice. This will grind the grains up a bit finer. The other think you could try is a longer mash. Go 90 min mash instead of 60. I would pick one or the other though. This way you know that if the problem gets taken care of, you know which one did the trick.

 

[RM-MN]

The first three causes of lowered efficiency are:
1. The crush.
2. The crush.
3. The crush.

All other causes are far below. Change the quality of the crush, changes the OG of the beer. If you get a really fine crush, your mash efficiency will be through the roof. Unfortunately, in a conventional mash tun you will also have a stuck mash. BIAB gets around this with a huge filter area so it doesn't clog but you can still get a better crush than most LHBS and not get the stuck mash.

Your wit is another story although related. Wit is a wheat beer. Wheat kernels are smaller and harder than barley so often with the LHBS mill setting they either are only slightly crushed or slip through without being crushed. If they don't get crushed well, the enzymes cannot get to the starch to do the conversion.

The answer to both your low OG batches is to get your own grain mill so you have control of the crush quality. If you want to experiment with BIAB and a very fine crush, you can expect your OG to be above what the recipes are expecting.