When you brew all grain any way to save time on a brew day can be a blessing, I’ve spoken about this before. Setting aside 5 – 6 hours can be hard to justify on a weekend if you have other responsibilities, so what about mashing overnight? Is it possible? Will it affect the beer?

The answer to these questions is yes, it is possible but also yes, it can affect the taste if not done properly so let’s take a look at the practicality of mashing overnight.

Mashing Overnight Or For Long Periods

Mash Overnight

The primary goal of mashing is to convert the starches in the grains into fermentable sugars. The way this happens is all to do with the enzymes that are active in the mash and the brewer has some measure of control over what enzymes are active by controlling the temperature.

The primary enzymes that the brewer wants to target are alpha amylase which is active between 66°C – 71°C (151°F – 160°F) and beta amylase which is active in the range of 54°C – 66°C (129°F – 151°F) with a certain degree of overlap.

The temperature of the mash can be controlled by the heating your brewing liquor, mashing in and then, in the case of an overnight mash leaving it for 7-8 hours whilst you go to sleep. The temperature of the mash will enable the enzymes to work and break down the starches.

All of the activity from those enzymes however stops when they run out of starches to break down or they denature and in most cases this is around an hour or sometimes less than that.

If you start a mash at a lower temperature of say 63°C – 64°C (145°F – 147°F) the resulting wort would be super fermentable a make a really, really dry beer which in most cases is undesirable.

Starting off at a high temperature if you are doing an overnight mash is going to be the ideal choice in most instances, a temperature between 66°C – 68°C (151°F – 154°F) will mean pretty much all the activity in the mash will be finished after the first hour. Then it can just sit there until you get up in the morning to run the wort out and finish the beer.

The problems may start to occur though if you lose too much temperature in the mash.

Losing Mash Temperature Overnight

Something that is very popular among both home brewers and commercial brewers at the moment is sour mashing which produces a sour beer by inoculating a mash with lactobacillus, and leaving the mash for a few days at a warm temperature to turn sour, the resulting wort is boiled which kills the lactobacillus and you end up with a quick way to make a sour beer.

Lactobacillus strains are cultured commercially and available to the home brewer to buy and this is what I would suggest you get if you want to make a sour beer. Lot’s of strains of lactobacillus also live on grain as well as other wild yeasts and bacteria, this is what may affect a beer that has a super long mash time.

Fortunately higher mash temperatures do kill a lot of the bacteria present on malted grains but not quite all of them. If you have ever left your mash tun full of grain after brewing and not cleaned it out you’ll notice a horrid “vomit” kind of sour smell. This is the bacteria we want to avoid having turn an overnight mash into a sour mash.

If the temperature drops too low to around 50°C (122°F) or less, then the lactobacillus and other bacteria has ideal conditions to multiply, the pH in the wort drops and you end up with a sour twang in your beer. Keeping the temperature of the mash as constant as possible is the key to overnight mashing.

Keeping Your Mash Temperature On Target

Simple measures are all that is needed to ensure the temperature of the mash holds for long periods. A few things to help maintain mash temperature consist of the following.

Insulation: Insulation of the mash tun is the most important, if you use a coolbox mash tun then there should already be a degree of insulation present. Take a note of how much temperature you lose over the course of a 60 minute mash or a 90 minute mash to get an idea of how well it will cope for longer periods.

Wrapping the mash tun up in blankets or a sleeping bag will also help maintain temperature and is an easy measure.

Ambient Temperature: If you brewing in the garage or in a shed where it’s likely to get chilly overnight then you are going to lose more mash temperature than if you keep the mash tun inside in a heated room. If you use a fermentation chamber and the mash tun will fit in there then you can help maintain a warmer ambient temperature and thus avoid big drops in mash.

Bigger Mashes: The more mass in the mash tun, the longer the temperature can be maintained. It’s not really ideal to do a small batch if you are going to mash overnight as you won’t be able to prevent the mash temperature dropping too much.

mashing overnight

Doing What You Find Most Enjoyable

If you take a look at the subject of overnight mashing there is a lot of debate as to whether it affect a beer’s flavour. There may be a minor effect but not a lot if you take a few preventative measures. At the end of the day not everyone can dedicate 5-6 hours straight to something when you have other commitments.

The best thing to do is to try it. If you make a beer and it tastes good then that is all the evidence you need to know that is works. If mashing overnight makes brewing more enjoyable for you then it’s definitely worth doing, after all that is why we all brew, because it’s fun.

Take A Look At Our Beer Kits, Always Fresh, Painstakingly Formulated.

We are working on awesome beer recipe kits which are on sale right now

Small batches you can make in your kitchen - Recipes are designed so you experience something new each month, whether that is a new variety of hop or a beer that fits in with the season. Enter your email below and we will keep you up to date with all the latest offerings.

Shop Now

We respect your privacy.

Neil /

Leave a Reply