Ask Mr. Wizard

Steam sanitation


Jeremy Ruetz • Rhinelander, Wisconsin asks,

I use a half barrel, with the center tube removed, for a fermenter. I like to fill the keg completely with water and then boil it for twenty minutes to sanitize it. Do I need to fill the keg completely with water, or can I boil a partially filled keg, letting the steam sanitize the rest of the surfaces? Which way would be more efficient or effective?


Heat, especially moist heat, is an excellent way to sanitize and
even sterilize brewing equipment. If you partially fill your keg with
water, bring it to a boil and restrict the flow of steam out of the
kettle you will indeed be steam sterilizing the surfaces above the
water level. An easy way to create a little back pressure in your keg
would be to insert a rubber stopper with a very small hole drilled
through the middle into the hole in the top of your keg. This
restriction will build a small pressure in the keg and help to vent air
from the keg and create a head space full of steam. Twenty minutes
is a common set point in heat sanitation techniques.

Heat sanitation works very well, but it’s not commonly used in
breweries. Most of these methods are expensive because of the energy
required, present certain safety challenges and can damage equipment if
conducted improperly. Some of the more dramatic failures caused by heat
sanitation are a result of a vacuum that forms when hot vessels are
cooled. If the vessel, for example a big and expensive fermenter, is
not properly vented during cooling the result is vessel collapse. This
whole cooling issue is another reason that heat sanitation is not
commonly used because cooling requires time and energy and most brewers
want to put their wort or beer into a cool vessel.

With this being said, we use hot water at Springfield Brewing
Company to heat sanitize our wort cooler, wort lines to the
fermentation cellar and our filter. The reason we use heat for these
areas is that it works very well. I had a very active role in designing
this brewery and I decided to use hot water in these areas of the
brewery and designed the process piping to permit this method to easily
and safely be used. Other brewers use heat in these same areas. It’s
also common to heat sterilize yeast propagation equipment. I use the
term sterilize here because yeast equipment is truly designed to be
sterilized with steam, similar to pharmaceutical equipment. The funny
thing with this comparison is that brewers were the ones who led the
way in pure culture growth on large scales and much of what is done
today in the biopharmaceutical industry came from brewing

If you like using this method and find it effective, then use it. I
do offer three suggestions: 1) use a thermometer to verify that your
temperature goal is met (we use 180 °F/83 °C minimum for our filter and
measure this at the discharge), 2) use a timer to make sure you have
held it for the proper duration, and 3) exercise caution since hot
water and steam can be dangerous when not respected.

Response by Ashton Lewis.