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How to Keep Your Wort from Boiling Over and Making a Mess

Some of my earliest attempts at home brewing would have made good viral YouTube videos.  I've transferred wort into a fermenter equipped with a spigot, only to find the spigot was open.  I've tried to get the last of a beer into the bottle from the bottling bucket, to see it overflow and end up on the floor.  I've nearly pulled a kettle of boiling-hot wort onto the floor trying to hook up the wort chiller.  Fortunately, I've not had any serious messes or a need to dial 911 yet...

One issue I struggled with a lot is boil-over.  When I made smaller batches, my kettle was just barely larger than the batch I was brewing.  More than a little foam meant that I ran a huge risk of boil-over.  A few times, when I stopped watching the boil to double-check a measurement or see what I needed to add next, foam crept over the sides of the kettle and made a mess.  Here are all the ways you can prevent boil-over in your next batch of homebrew:

  • Larger Kettles:  If your situation is like mine in the beginning, your brew kettle might only be slightly larger than your batch of beer.  If so, investing in a larger kettle may be a good answer.  Not only will this allow you to brew larger batches, but the additional head space in the kettle will give the beer room to foam up without boiling over the side
  • Fermcap S:  Although this foam-reducing agent is meant to reduce blow-off during fermentation, it's also useful during the boil to prevent boil-over.  A few drops added at the start of the boil will keep foam from forming on the wort and pretty much prevent boil-over.  I've been able to actually walk away from my kettle for 10-20 minutes at a time while using Fermcap.  It settles out during fermentation, so there are no worries about it affecting the finished beer or head retention.  Fermcap will cost around $5 a bottle, which is enough for many batches of beer. It's also useful in yeast starters to prevent blow-off.
  • Stirring the Pot:  Perhaps the cheapest solution on this list (since you probably already own a stirring spoon) is to simply stir the wort in the pot as it boils.  This requires more manual effort, since you'll have to be present at the kettle to know when it needs stirring, but is very effective and could cost you nothing.
  • Add Hops Pellets:  It's said that adding 3-6 hops pellets when the wort starts to boil will reduce foaming and boil-over.  Since you're probably going to be adding these anyway, it could be a no-cost solution.
  • Kill the Heat:  If you're able to lift the kettle off the heat or turn off the gas (electrics continue to provide heat when turned off), this can stop the boil and boil-over in its tracks.  When the foam is gone, re-apply heat and continue the boil.
  • Skip the Lid:  You shouldn't boil wort with a lid on it.  If you do, you're not allowing flavor-damaging compounds like DMS (dimethyl sulfide which gives a "cooked corn" aroma) to escape during the boil like you should.  Using a lid also means that when you remove it, there's a greater chance of foam building up quickly and overflowing.  If you're using a lid, stop.  If you need to channel the steam away from a surface like your kitchen cabinets, I've found that it can be helpful to use aluminum foil to direct the steam away.  I'll either create a very open "pseudo lid" that allows steam to escape in a direction that takes it away from the cabinet, or place the foil somewhere above the kettle to direct the steam away from the cabinet (e.g., in a V-shaped flap tucked in the bottom of the cabinet door).
  • Scoop off the Foam:  Some homebrewers simply scoop the foam off the top of the kettle and discard it.  This is a cheap and easy technique, but if the foam is growing very quickly you may not be able to move fast enough to keep ahead of it.
  • Spray Bottle:  This is another inexpensive solution.  Find a food grade spray bottle and fill it with water.  When the foam starts to rise, spritz the foam with the water.  This will destroy the foam, and given the small amount of water you're adding to the kettle with this approach, shouldn't lower the boil temperature.  Some home brewers keep a glass full of cool water or ice cubes near the kettle and pour some in if the foam gets too high.
  • Fans:  One homebrewer said that he took a computer cooling fan and mounted it on a clip, attaching it to the rim of his brew kettle during the boil.  The constant action of the air blowing across the top of the wort kept boil-over from occurring.  Given the price of a cooling fan and power adapter, this would be an inexpensive way to prevent boil-over.
  • Marbles:  Some brewers add 3-4 glass marbles to the bottom of the kettle at the start of the brewing process.  The marbles help to split up larger bubbles that cause foaming and boil-over.  Since they're made of glass, they don't melt or (assuming you clean them before use) contaminate the beer in any way.  This makes them another cheap solution.  Personally, I'd prefer not to put any glass inside my wort, just in case it breaks and leaves behind fragments that wind up inside a bottle... but it's your beer.
  • Coins:  For much the same reason that some brewers add marbles to the kettle to break up foam, others add 3-4 pennies or other small coins.  I'm personally against this idea.  Coins can be very dirty objects and have many tiny areas that might conceal something nasty.  They also contain nickel, copper, and other metals that might affect your beer.
  • Wooden Spoon:  It's said that laying a wooden spoon across the top of a boiling pot will prevent boil-over.  When the foam contacts the spoon, it breaks up the bubbles and keeps them from going over the side of the pot.  I've never tried this, and I'm skeptical of it given how fast foam can form in some worts, but it's a simple and cheap trick if it works for you.

So now you have lots of options to consider for preventing boil-over in your next batch of beer.


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