Overnight MashingContributed by the_stainQ: What is overnight mashing?A: It's as simple as it sounds -- overnight mashing is the process of letting your mash sit overnight, instead of just the 60-90 minutes most homebrewers are accustomed to. It could also be called "extended mashing" if you don't do it at night. For brevity's sake I will simply refer to the process as "overnight mashing" in this document.Q: What are the benefits of overnight mashing?A: The main benefit is time. If you don't have to wait around for a couple hours for the enzymes in your mash to do their job, you'll cut a couple hours off your brewday! It requires a bit of advance planning and scheduling, because you'll generally be doing the sparge and boil as soon as you wake up in the morning, but you'll be amazed at how early the brewday finishes! My typical procedure is to get the mash going around midnight or 1:00 AM, and then go to bed. I wake up around 6:30, make coffee, and start heating my sparge water, and I'm finished brewing and mostly cleaned up by 10:30!Another benefit many people have reported is increased efficiency. While most of us know how to check for conversion and to stop mashing when conversion is complete, many of us don't bother with the iodine test because our experience has taught us how long we need to wait. This can, and probably sometimes does, lead to lower efficiency as there may still be starches that aren't broken down, especially if you're only mashing for an hour, and even more especially at lower temperatures. With overnight mashing, you can be assured that your starches are as converted as they can get!Q: Are there any drawbacks?A: There are a couple of drawbacks, but they're not a big deal, and in my opinion -- the time-saving benefit made it worth the effort to overcome them. The first one is, as mentioned before, that if you mash overnight you'll be waking up and brewing beer first thing in the morning. For me, this ends up being about 6:30 AM because I want to be done with the brewday as early as I can in the day -- but I don't go to bed until 2:00 AM the night before because I don't even get home from work until 11:30. If you can start your mash a little earlier, or wake up a little later, it won't be a problem for you. You could also modify the schedule a little, doing an "extended mash" -- dough in sometime in the morning, go do your daily business, and come back in the afternoon to sparge and finish brewing.The other drawback is that you'll need to pay extra close attention to holding temperatures as steady as possible. I experimented with many coolers and setups before I settled upon one that held the temperature to my satisfaction. In a 6-hour mash, I typically lose only about 8 or 9 degrees F. If you lose too much, it can affect your efficiency (especially if you don't do a mash-out) because the sparge water won't get the grain bed hot enough to liquefy the sugars properly. I find that overnight mashing works best in combination with batch sparging -- I combine the first sparge water addition with the mash-out step by adding near-boiling water to bring the temperature up to around 165-168Â°F.Not only that, but if temperatures drop much below about 130F, you'll be prone to a lot more bacterial infections. This isn't really a huge problem, because everything's getting boiled anyway, but certain bacteria can cause off-flavors that will still come through in the finished product. Luckily, it isn't hard to keep temperatures up that high.Q: Won't my wort be super-attenuable and make a dry beer every time with this method?A: No. This is the question I hear most often, so I spent some time talking to professional brewers, reading textbooks, and studying the matter. Just as with a normal mash, the final fermentability of the wort is more a function of the temperature the mash starts out at, and not the temperature the mash finishes up at (as long as the temperature remains fairly steady over time.) It is possible to mash at a low temperature, say 140Â°F, for a very long period of time to come up with highly fermentable wort, and thus a very dry beer. Many of the "low-carb" or "ultra-light" beers available commercially are made with a similar method.However, an overnight mash at a higher mash temperature (150Â°F and above) will act pretty much the same as a standard 90-minute mash that starts out at the same temperature, even if the overnight mash ends up at a lower temperature at the end of the mash.As we know, alpha-amylase and beta-amylase are responsible for starch conversion. At a temperature of 150Â°F, beta-amylase will only operate for about 40-60 minutes before it becomes denatured; this happens quicker at higher temperatures, and a little more slowly at lower temperatures. Alpha-amylase lasts a little longer, but it is not as crucial in determining the final fermentability of the wort; its job is mainly to "de-branch" the larger starches into large sugars, so that beta-amylase can finish the job by breaking them up into even smaller sugars. So, even if alpha-amylase is breaking up the starches for a long time, they're still going to remain "large sugars" (less fermentable) because there's no more beta-amylase to break them down even further. Alpha-amylase itself will be denatured after about 2 hours at normal mash temperatures.In other words, after anywhere from 60-120 minutes, your mash is finished doing all it's going to do as far as conversion is concerned, and the rest of the time, it's just waiting patiently for you to come back and finish up.Q: Shouldn't I be worried about bacteria?A: Not really. Many beer-spoiling bacteria, including lactobacillus, don't survive a mash very well. Most lactobacillus strains cannot survive temperatures above 140Â°F. Some of it will indeed survive, but usually very little; this is the reason most people suggest adding fresh grain to a mash once it drops below 140Â°F when creating a sour mash. Any bacteria that survive the mash will be killed in the boil anyway, so that's not a big problem.As I mentioned before there are some bacteria that could potentially cause off-flavors even after the boil, but I have never personally encountered them. It is not likely that most of them would thrive, or even grow, unless the mash temperature dropped too far below 140Â°F or 130Â°F, and as long as your mash tun is insulated properly this should never be an issue.Q: What about tannin extraction?A: All of the information I have been able to find on this subject indicates that tannin extraction is much more a function of pH and temperature than anything else. My personal experience indicates that this must be true, because I have not noticed any astringency in any of my beers made with this method. Also, calcium can help prevent tannin extraction, so if this is a concern to you, add some calcium to your mash (always assuming you're staying within the proper boundaries of water modification principles) and it may give you peace of mind if nothing else.Q: Can I use just any mash tun?A: Yes and no. If properly insulated, I suppose any mash tun will do; I have successfully mashed overnight with a Zapap (double-bucket) mash tun in a specially insulated box and lost less than 10 degrees. However, it makes sense that the well-insulated your mash tun is to begin with, the less you'll have to do to insulate it.A lot of people in the homebrewing community like the Ice Cube coolers, and I can see why, but I don't recommend them for overnight mashing unless you can seriously insulate it. The problem with the Ice Cube is the same as the problem with many coolers -- I tested 3 or 4 different models before I found one that held enough heat to satisfy me -- it has to do with the way the lid is attached to the cooler. In most coolers, the lid is molded at the corners to have some sort of "pegs" or "posts" which snap into slots or notches that are molded into the cooler body. If you take a cooler of this sort, fill it with very hot water, seal the lid, and stand back, you will be able to see steam literally POURING out of the cracks around the lid.The cooler I use is the Igloo MaxCold 52 quart model. It alleges to be able to hold ice frozen for up to 5 days in hot weather, and I believe it. It is massively insulated and the lid is actually held on with separate door-style hinges so that it seals completely all the way around the cooler. This goes a long way toward preventing heat loss in an overnight mash situation.Q: How can I insulate my mash tun?A: There are probably as many answers to this question as there are homebrewers. Some people suggest keeping the mash in a 150 degree oven (if you have an oven big enough to hold your tun!) Others have built insulated or heated boxes of various types. Personally, I cover the cooler with a Coleman "emergency blanket" -- these are also sold as "space blankets" and are the thin, silvery, Mylar-like blankets sold for camping and survival purposes. When I mashed with a Zapap I lined a cardboard box with the same material and set the bucket inside; it worked extremely well. For my rectangular cooler, I simply cover it with the blanket, which I sort of tuck under the corners, and then cover the entire thing with a heavy quilt. I generally mash at around 153-158Â°F (depending on style) and when I take a temperature reading in the morning right before I sparge, I'm usually in the 145-150Â°F range (I tend to lose a bit less heat in the middle of summer and a bit more in the middle of winter.) Losing 10 degrees of temperature in 5-6 hours is perfectly acceptable, especially if you're mashing over 150F, which I almost always do anyway.Overnight mashing seems to be gaining popularity among homebrewers I know as a good way to save time, and with good reason! If cutting time off your brew session by splitting it up like this appeals to you, I encourage you to give it a try.
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