Preventing and Dealing With a Stuck Mash

A Stuck Mash Should Never Ruin a Beer

Mashing is the process of combining a mix of milled grain and water and heating this mixture in a vessel called a 'mash tun'.
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There are many reasons to be worried about a stuck mash. It can cost you time. It can be messy. A stuck mash is frustrating and in rare cases may change the character of the final beer. But there are two very good reasons not to be worried. One is that a stuck mash is rare. With a well built lauter tun and properly maintained equipment you’ll probably never have to deal with one. The second reason is that a stuck mash will never prevent you from creating a beer. You might not wind up with the beer that you originally envisioned but that’s part of the fun of homebrewing.

Preventing a Stuck Mash

The best cure, as they say, is prevention. When you brew, make sure you follow a few simple guidelines and your chances of actually having a stuck mash will be almost zero.

Clean Your Equipment

This reminder might seem redundant. Homebrewers know that brewing means cleaning. But sometimes it can be easy to relax cleanliness standards for the equipment that touches the wort before it is boiled. There is really nothing wrong with that. Any microorganisms that could infect your brew will be killed in the boil. I usually clean all of my “before the boil” equipment with hot water. The heat loosens any sticky sugars hanging around that I didn’t find when I cleaned up from my last brew and removes anything that might influence the beer or create clogs.

My mash tun/lauter tun is a converted rectangular cooler. I use standard 3/4" PVC pipes with small drilled holes for the wort collection manifold. If you build a similar contraption, which works great for either type of cooler, never glue or weld the pieces together. It is helpful to be able to take it apart for cleaning. Grains and sugars will find all sorts of places to deposit themselves and create clogs. When you can pull these pipes apart you can see anything lurking inside or in the joints and clean it out. Don’t be concerned that leaving the manifold loose will create leaks. This is a system that is designed to leak so if you create a few extra places for the wort to seep out that’s fine. Just make sure that the manifold fits snugly and will hold together in the mash.

If you use a false bottom for wort collection then life is that much easier for you. Again, do not permanently secure it in place; you’ll never be able to clean under it well. Just give it a place to sit and trust the weight of the grain bed and water to keep it there. Make sure that it’s clean to the eye and you’re ready to go.

Maintain Your Equipment

This is another obvious point but one worth noting. If you’re ready for your first all-grain homebrew, then you know by now that this homebrewing as much a tinker’s hobby as it is a beer lover’s obsession. There is always something fix or a piece of equipment that could stand some improvement. The wort collection manifold for your lauter tun is one of the more fickle pieces of your brew tool repertoire. Another is the sparger, the other side of the healthy mash equation. These two systems need to be balanced, precise and controllable. Before brewing make sure that the spigots that control the sparger and wort collection manifold are both working properly, that water flows easily through the system, and that there are no significant leaks anywhere.

Don't Crush Your Grain Too Small

If you don't have a grain mill simply ask you homebrew equipment supplier to crush the grains for you. They’re pros and they know what they’re doing. I’ve never been burned asking them to do it. They may charge a buck or so to do it but it’s worth it.

If you do crush your own grains, be very careful about how small you crush them. Try to do no more than to break each grain in half. Anything more can leave bits of grain small enough to clog the holes in the manifold or produce too much dust which is nothing more than flour. This flour can create a mash clogging dough in your grain bed. It is better to err on the side of caution here. Letting a few whole grains through your crusher will only result in a slight loss in efficiency.

There's really no need to try to crush your own grains. If you're going to brew within a month or so of getting your supplies nothing will happen to the crushed grains in that time. You could probably even wait a bit longer but the dictates of the hops and yeast won’t allow that.<br/>
A word about dust – too much can be made of the dust resulting from crushing grain. First I should say that it is unavoidable. Even if you sit down with two pairs of tweezers and break each individual grain perfectly in half, you won’t be able to prevent dust. So if there’s a bit of dust at the bottom of the bag of crushed grains that you get from your supplier, don’t worry about it. Most of it will simply get washed into your boiling vessel where it’ll be sanitized, get suspended in the wort then fall away with the trub. The flour from ground grain can stick a mash as described above but it takes a considerable amount to have this effect.

The real danger of this dust to a successful brew is infection after the boil. There are naturally occurring microorganisms that live on the grain. They can infect a brew and completely ruin it. If you’ve ever had a deliberately soured beer like a Berliner Weisse, you have an idea of the effect that these little bugs can have. The dust can carry these microorganisms. If any of it finds its way into the fermentation tank without first being boiled infection is likely. This is why it is often recommended that you crush your grains in a separate area or the day before brewing. Here’s my solution. I don’t bother to clean my “after boil” equipment until I’ve started the mash when any danger of floating dust is gone. There is just the right amount of time to thoroughly sanitize my carboy and other equipment while I’m mashing.

Drain and Sparge Slowly

Slow and steady wins the race when it comes to the mash. Don’t let anything get you in a hurry. The main reason for the slow drain and sparge is to keep from disturbing the grain bed.

After conversion, turn the drain spigot on as slowly as possible. Once you’ve established a slow trickle let the wort drain out at that rate and no faster. The point of this is to let the bed hold its shape. The sparge should be just as slow. Anything more than gentle drips will cause the bed to start to collapse.

This can have a couple of negative effects. First, a collapsed bed will produce “rivers” within the bed where the hot water is channeled around deposits of sugar resulting in a less efficient mash. Second, when the bed collapses it can cause a stuck mash. Once the bits of crushed grain are shaken loose from the bed they can follow the water down to the holes in your wort collection manifold and in a short time clog each individual hole. Never stir or deliberately disturb the bed after conversion for the same reasons.

Dealing With a Stuck Mash

Sometimes mashes get stuck anyway. It’s not over, though. Remember, a stuck mash should never spoil a beer.

Is It Really Stuck? 

The first thing to do is make sure that it’s really stuck. It is better to wait another hour or so for a slow mash than to start mucking around with the situation. Actually, you can wait quite a while without seriously affecting the quality of the beer. Once I was making a brown ale and things were simply not going well. I got started late, had trouble crushing the grains and had to rush out to replace my propane tank when I was trying heat my strike water. By the time I was ready to start sparging the sun was beginning to set. I would have finished up but my mash started draining excruciatingly slow. It was down to drips. By this time I was too tired and frustrated to try to deal with it so I emptied all over my sparge water into the lauter tun, covered everything as much as I could, left the drain open and called it a day. The next morning, my boil vessel was full. I went ahead with the boil and the beer turned out just fine.

So, if you’ve got the time and patience you can let a slow mash go at it’s own pace. I would never recommend emptying all of the sparge water as I did. Sparge at a slow enough rate to match the drain.

But, if you truly have a stuck mash or you simply don’t have the patience to wait it out here are a few ways that you can get it unstuck.


The first thing that you can try once you’re committed to the problem is to stir the mash. This advice is in direct opposition to what I said earlier but once the mash is stuck there’s no need to try to maintain the grain bed. If you’re trying to correct a slow mash then this step might stop it completely.

When you stir, try to scrap the top of the wort collection manifold to loosen any grains that may be clogging the holes. If this works it could be a temporary solution as whatever it causing the problem will likely repeat itself. You might have to occasionally stir and scrap until the mash drains completely. This could cause some of the grains clogging the holes to be pushed through and wind up in your boil vessel. A few grains won’t hurt but if it continues, grab a colander with fairly fine holes and run the wort through it. Too many grains in the boil can affect the character of your beer.


If stirring doesn’t help the problem more drastic measures may be in order. Gravity drives the drainage system so any clog is held in place by the constant pressure of the wort and grains trying to get past it. A quick shove on the other side of the drain can fix the problem.

Open the drainage valve all the way and blow into the tube with a quick sharp burst. Remember that drainage tube could be quite hot so use caution. If this works, the hot wort will start flowing again quite rapidly so be ready to aim the tube away from your face and into the boil vessel. Once it’s flowing nicely, turn the valve back down to a trickle.

Remove Drainage System

If all else fails, it might be time to remove the drainage system completely.

The lauter tun isn’t really that sophisticated of a piece of equipment. Historically brewers have used a lot of tricks to filter the water out of the grains. Some brewers in northern Europe put down a bed of juniper branches over a single corked hole in the bottom of their tun. After conversion, they simply pulled the cork and let the wort filter through the branches, leaving the grains behind. How about some beer with your pine sap?

In England, some brewers used a similar tun but left out the branches. They simply let the grains flow. They would continually sparge the grainy wort back into the tun until the wort flowed clear. This demonstrates the importance of the integrity of a good grain bed. If allowed to, it will actually filter itself.

So, if you’re hopelessly stuck, removing the manifold in the bottom of the lauter tun might do the trick. Get a smaller pot and move the drainage tube to it. Have another small pot ready. Open the drainage valve all of the way. Stick a long spoon or whatever you use to stir the mash down to the drainage system. If you didn’t weld or otherwise fix it into place it should be fairly easy disconnect the manifold. The wort and grain will flow freely. When the first pot is full, move the tube to the other and gently pour the first pot back into the lauter tun while the second fills then switch them again. You shouldn’t have to do this too many times before the grains begin to filter themselves. When the draining wort is free of grains, move the tube back to your boil vessel and continue the drain and sparge as usual.

If the drained wort isn’t free of grains by the fourth or fifth switch close the drainage valve and pour any remaining wort back into the tun. Put the lid on it and let it sit for thirty minutes or so. This should be enough time for a bed to form again. After the thirty minutes are up, reopen the valve and try again. If the wort still contains grains after a few switches this method isn’t going to work for you.


Chances are you won’t get to the point but if everything else has failed you might simply have to run all of your mash through a colander. Hold the colander as close to the bottom of your boil vessel as you can. Hold the drainage tube as close to the colander as you can and open the valve. When the colander is fairly full of grain, turn off the valve and return the grains back to the tun. Once most of the wort has drained start the sparge water and continue draining through the colander.

After some of the wort has drained away and your mash becomes less soupy it might start to filter itself as described above. But it if doesn’t, there’s no need to worry. This will result in a mash and beer with little to no change in quality. Besides, you might end up with a great beer. The only problem will be in recreating it later!

Whatever happens, just keep trying. A stuck or slow mash should never ruin a beer. With patience, inventiveness and a few of the tips here you should be able to work around a stuck mash and brew a fine beer.

Sometimes mashes get stuck anyway. It’s not over, though. Remember, a stuck mash should never spoil a beer. With patience, inventiveness and a few of the tips here you should be able to work around a stuck mash and brew a fine beer.