A boil over when home brewing can create big a mess, especially if it happens on the stove top! Not only do boils overs create a big mess, they also increase the risk of losing precious wort and hops over the side of your pot.
First, let's take a look at what causes the pot to boil over… Wort and water contain a lot of dissolved gasses that are forced out of solution, making them 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 of the pot.
The risk of a boil over is largest as the wort is just beginning to boil. Wort is also at a larger risk of foaming and boiling over when you add hops or other additives to the pot, as these tend to act as nucleation sites. Nucleation sites assist the physical separation of solid, liquid, and gas. That usually happens in the early stage of phase change due to boiling, freezing, evaporation, or condensation.
Try these helpful tips with your next home-brew:
Splurge and go big with your pot:
Using a larger enough pot is important, allowing for an extra 1-2 gallons of space. For example, if you are using a 7.5 gallon pot, limit your boil to 5 gallons. Grain brewers should use a larger pot, minimum 8-10 gallons to make a typical 5 gallon batch.
Stir your pot often:
Stirring your wort as you start to boil will help break up the larger bubbles that can cause boil over, as well as reduce the foaming. Stay close to your pot and keep stirring to keep the foam down.
Add pennies and glass marbles to your pot:
Glass marbles are motionless and not chemically reactive and can be safely boiled. Some people use pennies. Having them in the bottom of your pot will break up the large bubbles reducing the cause of a boil over.
Use Fermcap in your pot:
Adding a few drops of Fermcap at the start of the boil will suppress the foaming and help to prevent a boil over. This is an inexpensive solution and works great for preventing the initial boil over. It may still get a little foamy, but the foam breaks up much more quickly. Excellent to use in starters on the stove top.
Leave your pot uncovered:
Covering your pot can result in foaming and boil over when you remove the cover. When you cover your batch of wort during the boil traps many volatiles such as DMS which you want to be released during the boil.
Use a spray bottle with cold water:
Spraying cool water over the top of the pot will control the foam and help to keep it from developing and spilling over the pot.
Skim the foam off the top of your pot:
Skimming the foam and proteins from the top as they form can help prevent the foam from building up more and keeping it under control to prevent a boil over.