mash tun design problem - heat retention and insualtion.

[burrowsbrewery]

I have really been enjoying my new hobby, I think the best part about is by brewing 1 gallon I get to try out a lot of different recipes in a short amount of time and I have got favourable reviews vs some popular commercial bottles.

I'm having a problem with mash tun design; I can’t get it to retain heat. I have to reheat my mash each time it drops below 66degC in the 90 min mash, this happens a lot. I realise that low thermal mass is the issue and ideally I want to be able to leave a mash alone with 1degC loss.

The main inspiration for my system is from this post (hopefully the pics will show up)
viewtopic.php?f=6&t=35046
The difference is I am using brew bags for now because I need to lift the grains out when reheating and I’m not making a false bottom or a manifold until this problem is sorted anyway.

I have tried the following:-
1) Placing the pot in an unlit oven after it has be warmed to gas mark 1 – no real difference, more difficulty reheating.
2) Covering the pot in tinfoil, suspending it in a larger flower pot, at using expanding foam to fill the void, the pot becomes a removable jacket. – Things improved things but I still had to reheat a few times.
3) I realised the air gap above the grain may be a big issue so I obtained a 4.5 L pot instead of the 7 L I was using (my total mash volume for a 6% brew is about 3.9 L). I placed the 4.5 L pot inside the 7 L pot and used loft insulation to fill the void. I monitored the heat loss from hot water and it was an improvement over the foam idea but still not good enough so I haven’t brewed with it.

I can’t be the only one with this problem. A friend of mine suggested using a material intended for this sort of purpose; I need a material that will completely reject the heat levels we a brewing at and reflect it back into the pot.

I can see foams/foils have been used in pictures of setups, what are they and where do you get them from?

Any other ideas?

Note: I can’t get a decent cooler in a ~5 L in size

[Jocky]

How much actual beer do you end up with from a 3.9L mash, and how much do you boil?

The reason I ask is that I would suggest that you use a bigger pot, insulated as you have already tried, but mash thinner and don't sparge. This will give you more thermal mass.

For example, make sure your mash is nearly up to the brim in the 7 litre pot, and then insulate all around.

[burrowsbrewery]

3.9L is the estimated total volume of grain and water based on 2.5L/kg in the mash tun, I am only using this type of figure for sizing vessels not brewing. I do a proper sparge after the mash, my aim is to use traditional methods. Various figures may seem alien to anyone who doesn't brew 1 gallon at a time.

[Jim]

I wrap my mash tun in an old duvet.

While it's a full size tun, I think the duvet makes a big difference to heat retention - I get a drop of maybe 1C over 1 1/4 hrs.

[burrowsbrewery]

How much grain and water is in the tun though?

[Jim]

How much grain and water is in the tun though?

Typically 4kg of grain and 14 l of water - but without the insulation it would drop drastically in a very short time.

Before I started using the duvet I had to use the element in the bucket to keep the mash at the right temperature despite the fact that I had a camping mat and keg jacket insulating it already.

[Jocky]

3.9L is the estimated total volume of grain and water based on 2.5L/kg in the mash tun, I am only using this type of figure for sizing vessels not brewing. I do a proper sparge after the mash, my aim is to use traditional methods. Various figures may seem alien to anyone who doesn't brew 1 gallon at a time.

I have almost exclusively brewed 2 gallon batches at a time, but have done 1 gallon too, so I understand the volumes.

I would mash at 5 l/kg, with 2 and a bit kg of malt and 10 litres of water, all put into a 17 litre pot. Pot was wrapped in sleeping bag, with a camping mat underneath it. I could usually get a drop of only 1-2 degrees over 90 minutes.

[burrowsbrewery]

Interesting, I had considered upping to 2 gallon but feel I would be side stepping the problem and that’s just not in my nature. I don’t compromise, I prefer to engineer my way out of it.

The goal of my system is to have a 3 tier setup with full sparge, this will allow me to change the beer character with different mash and sparge temps same as a brewery but in a 1 gallon laboratory style.

I'm going home today with some offcuts of neoprene and bubble wrap to do another experiment.

[burrowsbrewery]

Whats your mash tun made of Jim?

Sounds like mass is not the be all and end all.

[Jim]

Whats your mash tun made of Jim?

It's an old converted plastic brewing boiler (Electrim Bin) fitted with a false bottom and insulation.

[burrowsbrewery]

I can see the need for so much insulation.

Remembering science lessons from long ago It has stuck me that what I need to do is protect against is convection cooling by air. Air itself is a very good insulator but without containing it cold air moves in and replaces the hot air which is the principal behind a central heating radiator. A vacuum is best i.e. a thermos flask.

You can see the conductivity of different materials here: http://www.engineeringtoolbox.com/therm ... d_429.html

I think the steel pot needs to be in as little contact with 'room air' as possible, including the lid. I also need to pay attention to the edge of the lid, hot air is probably rising thought the gap and cold air is going in.

[lord groan]

If I'm being honest I'd start with a plastic pot not a metal one. Metal is such a good heat conductor that you're giving yourself a mountain to climb right from the start in trying to maintain temperature. I'd seriously consider a quality coolbox , maybe something like this if you're set on a small one.
http://www.ebay.co.uk/itm/Coleman-Excur ... 462537ba9d
One that is already foam filled between the skins, often the lids are empty so that might need filling with foam, then get some builders insulation board
http://www.ebay.co.uk/itm/CELOTEX-50MM- ... 4d2ae099ce
or similar, and make a tight fitting box to completely enclose the coolbox, then before use preheat with some hot water to 66c for 20 minutes or so to get the container and inside of the insulation up to temp.
Hopefully hat should make a dramatic difference!

[clarets7]

Have you considered some permanent low density heating for the mash tun? I'm thinking of the soil heating wire that you can buy, arranged around your mash tun. By controlling the voltage to the wire you should be able to match the heat input to heat loss, giving you your constant temperature in the mash.

[markm1878]

A small buffalo boiler or similar would be a decent shout. I have an 8l one which I got for free as a ebay seller advertised it as 30l. When it arrived, needless to say I was a little surprised, was refunded and told to keep it.
With one of these, you could build a pid temp controller, drop the temp probe in the middle of the mash and it will keep the temperature throughout. The pid wired to a SSR will send pulses of energy to the element when required. It learns when its over shot and adapts. You can carry on using your grain bag and keep it off the bottom using a cake cooling rack or something. To make sure the temp is uniform throughout, you could use a pump to recirculate throughout. Step mashes should be easy too, which opens up options to different styles of beer.

[burrowsbrewery]

Sounds a bit like a mini Braumeister. That just it you see, a soon as you start talking about heating Wort you have to think about recirculating the Wort. It becomes RIMS or HERMS, complexity and cost goes up.

I can do electronic control, it’s part of my job, but I am very keen on keeping it simple and traditional; 3 tier, gravity fed, false bottom, sparge arm, not heating of the mash etc.

You may well be right, electronically controlled heating may be inevitable. When I consider it I think to myself if you going to invest in electrical parts you may as well make a larger system. This goes against my original principal; a 1 gallon traditional 3 tier setup now and possibly a larger identical system in the future keeping the 1 gallon system for testing recipes. That’s the point you see, the ultimate recipe test setup. And it can only be a good concept if you use the same methods in both systems.