Boil evaporation and hitting gravity

[BYOHB]

I am doing PM with 3-4 gal batches.

I mash 3lbs - 4.5 lbs of grain in a 2 gal cooler, boil 60-75 min, add 1lb DME or sugars in last 15 min and chill with wort chiller to at least 90 deg F.

After checking SG I add to fermentor, then add chilled water to get final batch size.

My questions are:
1) Is there a lot of variation in grain absorption?
My collected wort seems to vary a bit. I get crushed grains from several HBS store.

2) Is there a specific evaporation rate that works.
My boils are not vigorous, due to a small side burner in my outdoor kitchen. It takes 45 min to get a few bubbles, about 30 after that to see a hot break (white foam collecting on top).

I just brewed JZ's Northern Brown, and the grains plugged the small holes in my mash tun copper manifold! So, I guess my first "stuck" sparge! Maybe a bad crush, since only got 70%. Otherwise it looks good so far!

Next up, a clone of BJ's Tatonka Stout! Big beer, 8.3% and lots of flavor! I hope !! Any other suggestions for this one?

I will be tweaking JZ's Russian Imperial Stout (sorry JZ )

[Bugeater]

There is not really a lot of variation in grain absorption that I have noticed. Most folks use the figure of 0.12 gallons per pound of grain. I use 0.125 gallons per pound. That works out to a pint per pound, much easier to figure in my head.

Boil off rate is a little trickier since it is a little different for everyone. It will vary with kettle geometry ( depth, diameter, and volume), the strength of the boil, and the relative humidity. You really need to put a volume of water equal to what you ordinarily boil in your pot and boil it for an hour at your usual strength of boil. Then measure the remaining water so you can figure your boil off rate. This rate, in gallons per hour, will remain consistent as long as you use that same pot at the same boil intensity regardless of the volume you start with. A boil off rate in % will vary with the actual volume you start with.

In general, 1 gallon per hour is a good place to start. On of my boil kettles boils off at that rate, while another one boils off at 1.5 gallons per hour. The one with a higher rate is a larger diameter.

On those rare occasions that I do a partial mash, I don't use a manifold. I use a large SS sink strainer that will saddle the top of my boil kettle. I slowly dump the PM wort through that and then pour a little hot water through that to sparge a little. It's a small enough volume that I don't get any oxidation.

Wayne
Bugeater Brewing Company