Designing new false bottom
I have problem with wort boiling over during the first 20 minutes of the boil. I think the problem is that my run offs are too cloudy in the beginning of the lautering and that too much particles going thorugh or beside the false bottom. The problem with a cloudy run off in the beginning might be a my own short coming as brewer but the other thing with particles going through must be solved with a new false bottom that is tight aganist the side walls and with the right hole diameter. I have seen home made false screens in England and Norway with a false screen of SS 3 mm thick and with holes with diameter of approx. 3 mm. The hole area could not have been more more than 2 %. Now I have slots which are 1*10 mm and the hole area is about 25%. I do infusion mashes with a grain depth of 65 cm.
(Or could it be any reason for boiling over)
Wondering if you can provide some additional information regarding your cloudy runoffs during lautering? Are you vorlaufing? If so, how long?
The foamover at the beginning of the boil could be from a number of factors which hopefully can be solved for you. Are you adding any hops at the start of the boil to reduce surface tension of the wort and eliminate foam? Do you regulate steam flow once the boil is achieved or do you boil with steam flow full throttled?
Just some intial questions to help pinpoint the issue of boiling over.
Yes I recirculate the wort until I have circulated the hole volume under the false bottom. But it tends to go through particles too during the hole lautering sequence.
Yes I add hops just before the wort starts to boil. This wednesday I noticed that there where no more over boiling after adding the second addition of hops (after 30 minutes of boiling.
I use hop pellets and I store them in a freezer, so when adding it can be blocks of frozen hop pellets, this bolck might go to the bottom of the boiler, ending up with a bad utilisation, or?
A good question about the power adjustment when the wort comes to boiling temp. I have a lanemark gas boiler (the flame is burning in a SS tube) with a half and full effect. So I use to go with full effect (150 kW / 20 hl) up 95 deg. celsius. And during the boil it will go for about 90 kW. I am going to check up (with the gas burner service company) how and if this half effect works. Maybe 90 kW is far to much? Any suggestions. The kettle is well insulated on sides and bottom. About 5% evaporation / hour.
I'm not sure I understand your vorlaufing technique. It sounds as if your recirculation on your Lauter Tun is piped under the false bottom. Is this correct? Typically you would resuspend this volume either on top of the grain bed or in the middle of the grain bed during vorlauf. How do you determine how much volume you have vorlaufed? Flow meter, visual clarity? I'm also wondering what the capacity of your kettle might be and how much volume you're trying to boil of this rated capacity. One last quesiton-Do you have any method to determine differential pressure that ensures you're not "sucking" the bed too much resulting in grain getting through the lauter screens.
The sweet wort is recirculated back to the top of the mash tun.
I estimate the volume from how many times the underback is emptied. (I have a underback made of glass with a pump which starts and stops at low and high level.) This estimation might be wrong. But my belief is that the wort is floating too much in the beginning which will not support a effective filterbed towards the false bottom. When the grain bed becomes "drier" an good filter bed is developed.
I have made a simple valentine arm of just adjusting the height of the hose which is connected to the underback. You´re right: when adjusting the hose downwards, it is very easy to do it to fast and it will result in a to fast withdrawal of wort which will result in a sucking of malt thorugh the false bottom.
Gross cap of the kettle is 2850 liter and wort volume before boil is between 2350 and 2150 liters.
I have a hose connected from the outlet of the mash tun. This transparent hose goes up by the side of the mash tun so I can see if the pressure under the false bottom is equal to the height of my "valentine arm".
I don't think you have that much of a problem. I think every kettle has a tendency to boil over in the first 15 or so minutes due to the formation of hot break. After the hot break forms and starts to settle out, the boil over problem goes away. Can you turn the heat down just a bit to slow the boil? About the false bottom, the false bottom doesn't act as a filter, the grain bed does. The false bottom mearly acts as a support for the bed. If you are getting excess particles into the kettle, you need to take a closer look at how you recirculate the sweet wort.
It sounds like you've tackled many things. I would try reducing the steam flow once you achieve a boil as I mentioned a few posts ago. The boilover issue can be a real safety concern. If you find you cannot seem to resolve the problem you may want to consider using an antifoam product that you can add to the kettle. It takes very little to do the trick if added at kettle full, problem is you should try to filter it out post-fermentation.
As for the grain getting through your lauter screens--try checking your mill as well to see if your milling too fine. Maybe you can afford to mill a little courser without losing much extract. Best of luck!