Overnight Mashing

                    by Mike Retzlaff

In a previous article, I wrote of what has become routine in my little brewery; overnight mashing.  Long before I wrote the article, I had gotten raised eyebrows and some flak about this technique from a number of concerned fellow brewers.  The fears were centered on the possibility or even probability of a bacterial infection.  These concerns are real even if they aren’t realistic.  The fears tend to go away when all the facts are considered.

First, don’t confuse overnight mashing with sour mashing.  German brewers, among others, have for years, utilized an acid rest to lower the pH of the mash.  Phytic acid is produced by enzymes in barley and will sufficiently acidify a wort in due time. Lactobacillus occurs naturally on the barley and will do its thing if given an opportunity.  I suspect that Guinness Extra Stout is made with a sour mash.  Many Flemish style beers rely on a sour mash in addition to a sour ferment.  However, the overnight mash is not a sour mash and this is why: sour mashes are done for long periods at low temperatures.

In commercial food services, steam tables and chill tables are used in the kitchen and buffet lines.  The chill tables are required to keep the food at 41oF or lower.  The steam tables are required to keep the food at 135oF or higher.  These temps have proven themselves to inhibit bacterial growth.  I have used the overnight mash since 2005 and have yet to experience a problem.  I use a well-insulated mash tun and my temps don’t normally drop into that danger zone.  It helps to provide a little extra insulation by wrapping the mash tun in a blanket or other such material to impede the loss of heat over an extended period of time.  With the lid snapped on, the mash is somewhat sealed against the atmosphere so I really don’t fear assault by airborne microbes riding on dust motes.  Again, my overnight mash is not, and does not become, a sour mash.

Most of the conversion is probably accomplished in the first four hours.  However, it would try the patience of Job to start the mash in the morning, hang around for four hours while it finishes, and then continue with the brew day.  Starting the mash in the evening, letting the mash work while you sleep, and then finishing up the brewing the next morning, does make sense.  This overnight method can be utilized with any style mashing.  Single infusion, step infusion, step or program mashing, and even decoction mashing regimens lend themselves to the convenience of an overnight mash. 

Overnight mashing is something that anyone can do and requires no special equipment.  You need only change the timing of what you’re already doing.  It can increase your brewhouse efficiency, help balance your wort, and it breaks up your brew day to utilize your time more effectively.  Overnight mashing is another tool you can use in your campaign to brew better beer.

Give it a try on your next batch and see for yourself.

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