Very Wierd Evap. Problem

[Trent]

Gday all
Just finished making my first German Pils, and my post chiller (copper sitting in ice) decided to clog up on me :angry: , so it is now sitting in the fridge waiting to cool to pitching temp. Anyway, I have a problem, that I am HOPING someone can help me with.
I have brewed about 50 beers on my current system, I have always allowed for 4L loss per hour to evaporation, always with the lid OFF, and have consistently hit my volume targets, to within about half a litre or so. All my water containers are marked, so I know exactly how much water goes where, and I am pretty anal about it all. Last weekend, to use up an extra 2L of fermenting brown ale (see my post last week!), I made an IPA. I only had a spare 23L carboy, so I decided to make it to 18L, plus the 2L of brown for a starter, so I would still have room for the krauesen. So, I mash in with 6.5kg of malt, and 15L of water, mash out with 6.5L of water, giving me (in theory) a 15L first runnings. I sparged with 9.5L water, to give me 24.5L into the kettle, -4L evap and 2.5L to trub, should be 18L.
Because it was a cold day, and my reg is pretty crap, I decided to, for the first time ever, put the lid 2/3 of the way across the top, to reach and keep a boil. I hit my preboil gravit target, and after whirlpooling, checked my gravity, spot on at 1070, then ran through the chiller, into the fermenter - 15L only. No water left in the grains, only the 2.5L left in the kettle. Hmmmmm.

Tonight, same maths to give me 54L preboil - actually passed my preboil target grav, and was smack on target for my postboil gravity. Only problem is, I boiled with the lid mostly on again (I have a hard time getting 54L to stay at a rolling boil, especially in winter), and instead of ending up with my expected 48L, I now have 41L. That is 7 effing litres more than my usual evap rate, and I am not happy Jan! I cannot work it out, I hit all my other targets perfectly, and usually do, within a point or so either way, the only thing I have done different than usual is boil with the lid mostly on. I always thought you would lose LESS to evap with the lid on. I am gonna make myself a calibration stick for the kettle this week now, never needed one before, but I cannot for the life of me work out where all this extra beer is going, and why my gravities are hitting the targets. I could understand the loss if my gravity was way up.
I'll shut up now, or I will go on about it all night :blink:
Any advice would be appreciated
All the best
Trent

 

[Ross]

Trent,

4l per hour is quite a small loss, I lose nearly double that - I can only assume by having the lid 3/4 on you've increased the vigour of the boil & hence your greater loss. Only having the lid fully on will prevent loss, the steam will just funnel out the gap...

c`heers Ross

 

[bigfridge]

Tonight, same maths to give me 54L preboil - actually passed my preboil target grav, and was smack on target for my postboil gravity. Only problem is, I boiled with the lid mostly on again (I have a hard time getting 54L to stay at a rolling boil, especially in winter), and instead of ending up with my expected 48L, I now have 41L. That is 7 effing litres more than my usual evap rate, and I am not happy Jan! I cannot work it out, I hit all my other targets perfectly, and usually do, within a point or so either way, the only thing I have done different than usual is boil with the lid mostly on. I always thought you would lose LESS to evap with the lid on. I am gonna make myself a calibration stick for the kettle this week now, never needed one before, but I cannot for the life of me work out where all this extra beer is going, and why my gravities are hitting the targets. I could understand the loss if my gravity was way up.
I'll shut up now, or I will go on about it all night :blink:
Any advice would be appreciated
All the best
Trent

Hi Trent,

Sorry to hear of your woes but at least the volume/gravity relationship is an easy one to control.

Over the years there has been a few bits of my brewing gear that I have found to be essential (after the hydrometer of course). They are:

- Dipstick to accurately measure volume in boiler
- Stopwatch to keep track of the boil time (particularly of you have someone 'helping' you on brewday)
- Brewing software to do the calcs for you (I use Beersmith) but this is only required to work out the volumes and gravities you should get.

If you know what gravity and volume you have in the kettle before boiling then you can predict what you will have at the end. Any variations can be adjusted by topping up with water or boiling a little longer.

David

 

[Stuster]

I think Ross is spot on, Trent. I also lose more than 4 litres an hour, usually more like 8 litres for a 90 minute boil. But yesterday I lost 8 litres in a 75 minute boil. I wasn't keeping that close an eye on it and the boil was just really vigorous.

 

[BottleBitch]

Ross is right, it will increase the vigor of your boil and increase the evaporation rate, your normal 4 liters an hour is not much and it would seem that you need a few more BTUs under the kettle, losing more is a good thing, the higher the vigor the less the boil time, some big breweries use an external calandria to heat the wort and this gives them a boil time of just 60mins. If you find that at the end of the boil your gravity is high because of this just add some hot liquor and boil for two more minutes and recheck your gravity, if you dont hit volume or gravity targets in the kettle try adjusting your efficiency % till you do, I always check exactly what my kettle preboil volume and gravity are and adjust from there, because if you dont your color, bitterness, cold wort volume and al/v will all be out of spec.

 

[Trent]

Hey Guys
Thanks for the replies, and I will take them all on board, starting with the dipstick, and then trying to get a higher pressure reg for my 3 ring burner. I have no problems allowing for more evap with a more vigourous boil, its just that I lost nearly triple my usual amount, and it was only a 60 min boil, and with my IPA, I lost nearly double. Were it the same amount lost for both brews, I could easily accomodate that. I usually hit 75-78% efficiency for a single batch, and 80-83% for a double batch, and obviously, if I hit my target gravity, and was 7 litres down on my target volume, my efficiency has also gone out the window. I use a marga mill, with the adjustor taped in place, it has served me well over the last year or so, always getting good efficiency, maybe the tape has let go a little? Anyway, I now have a few places to start working out my new "system losses", so thank you for the help.
All the best
Trent