'Top on' or 'Top off'... for the boil!

[nickrjsmith]

Hi People,

The last time I did a boil I left the lid kind of over the top of my urn (I boil in a tea urn). The beer turned out fine. What's the merits of boiling to reduce water Vs boiling with enough and keeping a top on so to speak....

Nick

 

[IrregularPulse]

You want to keep the top off. You can put it on to help reach a boil, then remove. There are compounds you are boiling off that can lead to off flavors if collected and dripped back into your wort. DMS being the main one. It can lead to a buttery off flavor.

 

[Toasted678]

Tops always off... mandatory.

 

[nickrjsmith]

OK - so if it's top off, in my Urn which holds 27 litres with a little head room, is it OK to keep topping it up?

 

[COLLINH]

No matter how much head room there is you don't want the top on during boil or it will give bad flavors to your beer.

 

[brodie113]

Top off for sure. DMS has a cooked corn/vegetal flavor & aroma.

 

[freakshow10mm]

You want to keep the top off. You can put it on to help reach a boil, then remove.

This is what I do. Help hold the heat in to get to a boil faster, then leave off during the boil.

 

[nickrjsmith]

Ok but can I top up as I go?

 

[freakshow10mm]

I wouldn't. Fill your kettle to the recipe and do the boil. When you're done, then top it off with clean water.

 

[MNDan]

Hmmm. I seem to remember a very long discussion regarding this on the HBD a long time ago. I think there was a consensus that a partially covered boil was the way to go to prevent hot side aeration while still letting the DMS boil off/not condense back into the wort.