A boil over when home brewing can be a real mess, particularly if it happens on the stove top. Even if you are brewing outside, you risk losing precious wort and hops over the side if your pot boils over. So this week I provide some quick tips on avoiding a boil over.
Why the Pot Boils Over
Wort and water contain a lot of dissolved gasses that are forced out of solution, which is why they are prone to boil over. Wort made with malt contains a lot of proteins, which also tend to foam as they start to boil, and often the foam is what goes over the side.
The risk is largest as the wort is just starting to boil. Wort is also at risk of foaming and boiling over when you add hops or other additives – as these tend to act as nucleation sites. Wort that is starting to boil can really foam up and boil over if you add hops to it.
Wort that boils over on the stove can create a real mess. The brewer is faced with either having to turn off the heat and clean up the mess, or continue with the boil which effectively bakes the wort on the stove – making it really hard to clean up.
Methods for Stopping a Boil Over
- Get a Big Enough Pot – Using a pot with sufficient headspace is important. You don’t want to try to boil a pot that is full – an extra gallon or two (4-8 liters) of space is required in a typical 5 gallon (19 liter) batch. For 5 gallons/19 liters of extract, this means getting a 5 gallon (19 liter) pot and limiting your boil to 3.5 gallons (14 liters). For all grain brewers, you need a much larger pot – typically 8-10 gallons (30-40 liters) to make a typical 5 gallon (19 liter) batch.
- Don’t (ever) Cover Your Pot – Covering your pot while heating can result in foaming and boil over when you remove the cover. In addition, covering your wort during the boil traps many volatiles such as DMS which you want released during the boil. So don’t cover your pot when boiling.
- Stir the Pot – Stirring as you start to boil will help to break up the large bubbles that can cause boil over as well as reduce the foaming. Stirring also keeps you focused on the pot, so you can turn down the heat or remove heat if needed.
- Use Glass Marbles – Some brewers add glass marbles to their pot. The glass marbles (don’t use plastic!) are inert and can be safely boiled, and having them in the bottom of your pot will break up the large bubbles that are the main cause of boil over. Some brewers also use pennies, but I try to avoid adding metals such as copper which can impact the stability of the finished beer.
- Use Fermcap (foam control) – A few drops of fermcap at the start of the boil will suppress the foaming and help to prevent a boil over. This is a very effective solution, and relatively inexpensive.
- Use a Spray Bottle with Clean Water – Spraying cool water over the top of the pot will suppress the foam and help to keep it at bay.
- Skimming – Though I’ve not used this method myself, some brewers report success with skimming the foam and proteins from the top of the boil pot as they form. If you can prevent the foam from building up, it won’t be able to boil over.
Do you have your own ideas for reducing boil over? Leave a comment below!
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