Sour Mash How-To - Brain Sparging on Brewing


Sour beer, saisons, farmhouse beer, homebrewing, ramblings

October 15, 2010

Sour Mash How-To

As sour beers are gaining popularity people are looking for more information and more ways to homebrew them, especially ways to shortcut the generally very long souring process. Sour mashing, in particular, allows natural growth of lactobacillus, a common spoiling microorganism, to create lactic acid that contributes a slightly sweet sourness. If it is not the most common sour flavor, it is definitely among the top of the list. Although lambics tend to be the most well known sour(ish) beer, the world of sour beer is very diverse. There are traditionally sour styles, such as oud bruin and Berliner weisse, but most beer styles can be soured. After all, before refrigeration, pasteurization and increased sanitation, most beers were subject to souring over time. Some styles, such as porter, were given greater quality as they aged (for a certain amount of time) while some, like many wheat beers, were considered ruined once souring set in.

Brewers can use sour mashes in a variety of ways. It is a great way to clone Guinness and some other dry Irish stouts, which used soured beer to develop that sharp tartness. It can be used to create the reviving Kentucky common style. It can be used to simulate Berliner weisse and other traditionally sour styles without having to make additions post-boil. Of course, if you just want to add some sourness or complexity to any other beer style, a sour mash can provide an easy option. I’ve seen sour brought to all sorts of styles. Browns, tripels, IPAs, etc.

There are many ways to sour beers and like everything else in brewing, the process has varied flavor components. Instead of sour mashes, brewers can also bring lactic acid into their beer in several other ways. It is common to introduce lactobacillus after the boil before, along with or after saccharomyces. Most of the sour mixes from Wyeast or White Labs contain a blend of lactobacillus, saccharomyces and other souring playmates. Brewers can add lactic acid post-fermentation. Acidulated malt/acid malt may be added the grist, because it is malted barley coated in lactic acid.

Each of those options contributes sourness in different ways. Acid malt is definitely the easiest and most uniform method of souring beer pre-boil. It adds uniform sourness without needing to introduce any bugs into your brewing system. Some people believe adding lactic acid to the mash gives a harsher sour flavor than natural souring with lactobacillus. It can also mess with the mash ph and require an amylase addition to ensure conversion. Similarly, people believe lactic acid additions post-fermentation provides uniform sourness at the expense of flavor. While I can’t say I know the difference, for homebrewers without such a distinguished palate, lactic acid adds an expense to brewing you may not want. Adding a complex of bugs to your brew is really the best way to get that complex sour taste, but if you are looking to add some sourness without the whole package, then a mix of bugs may not be in your best interest. The other downside is that you do have a tremendous wait on your hands (generally at least a year) before fermentation is complete.

There are downsides to sour mashes as well. Sour mashes are dependent on temperature, it is difficult to obtain the same level of sour flavor across batches, and they can be infected with the wrong kind of microorganism, resulting in a failed sour mash. They are easy to perform, provided you follow a solid process and sanitation (like anything else in brewing!) and trust your beer when it smells like rotten milk. Like all things sour, it relies on techniques that oppose most of what brewers live by in making any other kind of beer.

I will explain two different processes for sour mashes, along with some ideas why one might want to choose a particular option. I’ll start off with some basic information, and then split off into the different processes.

Basic Information

Regardless of the methodology, a sour mash works the same way in all three methods. A sour mash is basically a really long acid rest. In both types of mash, lactobacillus spews lactic acid into the mash. While the purpose of an acid rest is to slightly lower the ph of the mash, the goal of a sour mash is really more about flavor (although it has the same result.) Lactobacillus is a bacteria present on, well, a lot of things. It is on malted grains and it is always present in your mashes. Normally mashes occur around 150-160, which is a little too warm for lactobacillus so there is no souring when you start the mash that warm. When you do an acid rest or a protein rest, then lactobacillus gets to join the party. Sour mashes can be done in 24 hours or as much as several days, depending on how warm you keep your mash and how sour you want your beer.

It’s important to know how sour you want your beer to be and the effects of that sourness. At low levels, lactic acid will give beer a tangy sweet-sour flavor, like drinking lemonade. At moderate levels it will add distinct sourness. At high levels, it will dominate the beer and make it truly mouth puckering. When you start to consider higher levels of sourness, remember that lactic acid only produces one flavor. Many sour beers – particularly those of Belgian descent – are soured by microorganisms producing lactic acid, acetic acid and the unmistakable byproducts of brettanomyces. By only souring with lacto you will not get the complex sourness produced by the blend of critters in those beers. You may find strong lacto souring to be boring in its unitary flavor. Think Berliner weisse, not oud bruin.

Lactobacillus does its thing at temperatures from 90-140. At the lower end it reproduces and generates lactic acid slowly; at higher temperatures more quickly. Although it does live at temperatures below 90, it does not survive well above 140. For this reason, temperature control does matter in a sour mash. It is especially important that the sour mash stays above 90 as much as possible to make sure lactobacillus can multiply and sour the mash quick enough to prevent any other critters from taking hold and making your sour mash and foul mash. Lacto should naturally reproduce faster than anything else present in the mash and crowd out any party crashers.

Another important piece of a sour mash is to restrain oxygen contact as much as possible. This is simply done by covering the sour mash. Lactobacillus can function anaerobically, so by restricting air contact you prevent oxygen from reaching critters that only grow aerobically as well as cutting off the ability for them to land in your sour mash. Although you could sour mash in a fermentation vessel, this is probably a bad idea because lactobacillus is a spoilage agent in fermented beer as well. You don’t want to lose a good fermenter (or airlock, tubing, stopper, etc.) to a permanent lacto infection. On the subject of equipment, do note that sour mashes may develop a krausen and may vent gas. You do not want to seal up a sour mash in an airtight container. It needs to be able to vent, just like during fermentation.
Sour mashes stink. Until you have experienced them and can recognize the smell as something distinct from anything else you have smelled (and I hope you do not have a lot of experience smelling lacto infections around your house) your brain will try to attach what you are smelling to something you have smelled in the past. To me, I think it smells like creamed corn gone bad. Some people smell rotten milk, rotten cream, rotten butter. It will have a rotten milk smell, because lactobacillus is what makes milk, well, rotten. Don’t be scared. Your final product, while it will have sourness and may have some of that lacto smell, will become a tangy, sour beer once fermentation is done.

If you are looking for consistency in your sour mashes from batch to batch, as usual the most important concern is temperature control. If you mash three days for one batch and three the next, without temperature control you’re going to have different levels of sourness. It can be difficult to maintain high temperatures for days at a time. One suggestion I have is to test the pH. pH will tell you how acidic your mash is, so that’s a good way to try to develop some consistency. Once you figure out how much sour mash at what pH is desired for your beer, you can replicate the same pH. It will take some experimenting to figure out how sour you like your recipe. Regular beer mash pH strips will be too high on the scale. You will need to pick up some mead or wine pH strips as they reach into 3-4 range. You can also buy an electronic pH reader.

Lastly, extract brewers can participate in the fun. I will provide extract instructions at the end of each section. Ok, on to the actual process!

Version One: The Full Sour Mash

In this version, you will make the whole mash into a sour mash. This will make a very acidic and sour beer, especially if you let the mash sit for several days. Because of the volume, the primary concerns are keeping the temperature up and preventing anything from beating lacto in controlling the mash. If another critter takes over and ruins the mash, you’re going to have to dump an entire batch’s worth of grain. This will be easiest to perform if your mash equipment is set up with a heating element in the mash tun, so that you can apply heat regularly through the day to keep the mash within the appropriate range. An additional concern is that if the mash pH falls too low, you will have a hard time extracting enzymes for the regular mash, so adding amylase enzyme may be necessary to get that starch to become sugar.

This sour mash style would be useful in making a Kentucky common beer, a Berliner weisse (without having to worry about lacto post-boil), or if you just want to make a sour beer. On that last note, this is really the most functional way you could make a very sour beer with a lot of hops because lacto cannot withstand the antibacterial properties of hops. Needless to say, unless you plan on mashing for a few hours to get a hint of sourness, you better plan on enjoying a very sour beer. You’ve been warned! In my opinion, this is not a good first run method, unless you are already a master of sour beers and have no fear of a mouth puckering beer.

This is really very simple. Mash as you normally would for your recipe, leaving 4-8 ounces of your base malt behind. Complete your mash up until the point you would sparge. Instead of sparging, let the mash cool to around 130. Once it has reached this temperature, stir in the grains you left out. Next – and this is important – cover the mash with either saran wrap or foil. It needs to completely cover the liquid and you need to push out as much air as possible. This is much easier with saran wrap because you can work all the air bubbles out to the side. With foil you can gently push down from the middle and work outward to get a good seal. Some people are concerned the saran wrap will leech off flavors into the mash because it’s not made to be heated. I’ve never used it so I can’t say one way or another but I’ve never read an instance where somebody who did use it discovered any detectable flavors.

What you do next depends upon the equipment available to you. If you have a heating element in your mash tun, you will want to gently heat up your mash 2-3 times per day to keep it warm. If not, then you at least want to wrap the mash tun in blankets and keep it in the warmest part of your house that you can. If it can sit near a furnace, running clothes dryer, etc. this is preferable. You could try making a reverse swamp cooler by submerging the mash tun in hot water and periodically replace or reheat the water. This might be useful if you choose to pour the mash into a bucket or other container that you can fit in the larger container for hot water. I suspect this to be a losing battle with that much hot water. Even if you are trying to keep several gallons at 110F you’re talking about keeping the water 30-40F degrees hotter than the ambient temperatures. That’s a lot harder than using a swamp cooler to keep water 10-15F degrees cooler. However, work with what you have and what works best. If the mash gets down below 90, I suggest finding a way to warm it up as soon as possible. Infuse a small amount of very hot water or put some hot water bottles around it. You really need to do something.

Depending on your preference for sourness and sour mash temperature, your mash could be at the desired sour level within 15 hours. You may even find yourself sour mashing for days, particularly if you love sour or you have trouble keeping the mash warm. The only way you’re really going to know how sour you have made your beer is by measuring the pH, which is why I encourage you to either purchase the pH strips in the 3-4 pH range or an electronic pH detector. Unlike many things in brewing, you’re probably not going to want to taste this one unless you are very, very daring.

Once you’re happy with your sour mash, it’s time to clean it up and sparge. Throw out the foil/saran wrap. You may find a layer grey-brown gunk on the top. Do not fear it. Skim it off and throw it out. You don’t have to be precise, but it’s better to get rid of as much as you can. Once you’re done, sparge away. You may find the runnings smell horrible. You may even find this smell carries over into the boil and into the fermenter. Don’t worry, it does mellow (to a degree) during fermentation and conditioning.

Let me say this, before you rush off to give it a go. You are feeding several gallons of thick, sugar rich liquid to very voracious bacteria. It will love you for giving it so much food and so much warmth. It will repay you with lactic acid. A lot of it. For your first time out, you may want to limit yourself on how long you let the sour mash go. The Joy of Homebrewing suggests stopping at the 15 hour mark. Unless you are a real serious sour beer lover, you will be happier wading into sour mashes rather than leaping right in. If you over sour your beer, you can either blend it with non-soured beer or you can add unfermentable sugars, like lactose to balance out the sourness. Unfortunately, there is no way to remove the lactic acid.

For extract brewers, you can add your extract and any partial mash to your boil volume of water, boil for about 10 minutes to fully dissolve the extract, cool to 130, pitch some fresh malted barley (2 row, pale malt, pilsner, etc. will work) and let it sit covered in the same manner until the desired time. Once you have reached your destination, skim the top, pour it into your kettle and proceed with the boil. Make sure to add any lost volume back in at the start of the boil.

Version Two: The Partial Sour Mash

Personally, this is my preferred method for adding sourness to Belgian-style sours. I find that it is easier to control, easier to work with from an equipment standpoint and produces the same results with less risk. The idea, as the name suggests, is to sour mash only a portion of the grain and then add the runnings to the boil. It’s a lot easier to keep a small amount of liquid warm than a large amount, so it’s definitely the more efficient route. The downside is that you can only get so much sourness out of it. Lacto will reach a point where it has dropped the pH to a level that it cannot continue to reproduce, so it will stop and go to sleep. Unlike a full sour mash, which usually will be ready to go in a day (maybe two), you may have to let your sour mash run for 2-3 days (or possibly more) if you are trying to get maximum sourness.

Because you have the flexibility to control your sour mash volume, this is an easier way to add sourness to really any kind of beer. You can do very small sour mashes or very large sour mashes. You could still do a Berliner weisse or a Kentucky common this way, but you may not get as much sourness as is necessary for the style. As with the full sour mash, you will want to keep track of the pH to be able to replicate your results.

The process is simple. Mash the desired amount for the sour. If you have decided on 10% of the beer as a sour mash, you can use an equal amount of the grain bill. There’s no reason to use specialty grains, so just take that portion as base grain. Keep a small handful of grain to the side. When I do this, I usually just do it BIAB-style (brew in a bag) on the stovetop. I mash for an hour around 150. I think of it as a full mash session, so I will mash a small amount of liquid and then sparge a slightly larger amount to make sure all the sugar is removed from the grains. I might do 1/3 water to the mash and 2/3 to sparge. If you are trying to do a high ABV beer this may not give you enough water for both mash and sparge, in which case you will either have to forego sparging or sour mash a smaller amount of grain. Once complete, discard the grains. Let the runnings cool to 130F. You will add the grains kept aside to introduce the lacto to your sour mash.

You will, of course, need a container for the sour mash. Some people use a small thermos, some people use jugs, you can use anything you want as long as it does not seal airtight. It is preferable to use a container with minimal headspace; and if possible cover the mash with saran wrap or foil as explained above. I use a half gallon growler with foil secured over the top, like a yeast starter. I leave it in the sink surrounded by hot water and I periodically reheat the water to 135 and let it cool to 90 before reheating. It isn’t exact or precise, but it’s what I can do with the available equipment. It allows me to minimize headspace by filling it up into the neck. I can’t completely seal it off, but between the minor surface area and the foil over the mouth of the growler, there’s minimal chance of non-lacto infection.

Because this method leverages convenience over volume, you will need to let the sour mash sit for longer (perhaps 2-3 days) until it reaches terminal pH. You can check pH as necessary, but in the future you should rely upon changing the sour mash volume instead of duration of time to adjust how sour your beer ends up. You will want to match up the end point for your sour mash with the start time of the boil, so you will need to complete your regular mash as usual in the final few hours. Once you have all of your regular mash runnings in the kettle, add the sour mash. If you can skim off the crap at the top, do so. If not, it’s not the end of the world. It’s preferable to strain the sour mash and catch the grains you put in, so they don’t boil and add unnecessary proteins to the beer. If you use the same strainer for straining your wort as it goes into the fermenter, don’t forget to boil the screen for a couple minutes and/or spray down with sanitizer so you don’t get lacto going into the fermenter.

Very simple. Just as you likely want to limit the length of time for your first full sour mash, you will probably want to limit the size of your partial sour mash. I find 15-20% adds very noticeable sourness. 15% is a good place to start and you can bump it up as necessary. As I mentioned at the end of the full sour mash discussion, you can’t undo lactic acid once it’s there. You can try to work around it, but that’s it; so it’s better to start light and work your way up.

Concluding Thoughts

While a sour mash is no replacement for the complexity of a lambic or Flanders red, it can accurately be used in many styles and serve as a simple substitute that will get you in the neighborhood of some of those great, complex sour beers. If you want to try souring a brown ale, it’s considerably easier to do it pre-boil than post-boil, where you risk infected equipment or having to buy multiple post-fermentation items to keep lacto out of your non-soured beers.

Some people do advocate some other sour mash methods I didn’t address. It has been advised that the partial sour mash be dumped into the regular mash at the beginning to increase the sourness. The problem with that idea is that lacto generally dies off above 150 – mash temperatures – so you’re not going to do much good that way. Also, some people advocate adding the sour mash in the fermenter. While this is probably a good idea for creating a Berliner weisse, especially no-boil style, it gets you back to the issue of having lacto in your post-boil equipment and you risk infecting future batches if that equipment is used on non-sour beers. You also forego the benefits of the boil in breaking down proteins and other nonsense in the mash to make a clearer and cleaner beer (again, not an issue with Berliner weisse, but there’s no reason to make other sour beers cloudy).

So there you have it. A nice little treatise on sour mashes. I hope it’s helpful. Good luck!


  1. Hey I've got a few questions about brewing a berliner weisse up. Any chance I can pick your brain? Shoot me an email at if you have time.

  2. I really, really appreciate this article. It makes the different options pretty clear. I am leaning towards the partial sour mash with as much as 25%, though I may even up it. I want to do a sour golden strong ale and see how it comes out.

    I do 1.25 gal batches (though differently than you suggest) so size isn't too big of an issue. I was thinking of putting the sourmash into my slowcooler with the STC1000 probe and keeping it around 120F. Since my pre-boil is less than two gallons, there is no way, even at 50%, that I'll need more than 1 gal of water. Around 1/2 gal is actually about the minimum for the slow cooker so I was thinking of putting some containers full of water in to take up space. Or, maybe put the sour-mash into a container and use the slow cooker as a water bath. Basically, whatever I need to do to hold the temp. However, do you know if I should worry about the liquid being in contact with the slow cooker? Maybe I'll just add boiling water and keep it on high for a few hours afterwards to kill any remaining bugs (not that anything else will need to sit in it. I just want to be sure). Any thoughts