Saturday, 28 February 2015

Making diastatic brown malt

When I got my current job, which involves malting as well as brewing, my first thoughts were could I make diastatic brown malt? To someone not a beer obsessive this might sound slightly odd but bear with me.

Historically brown malt was made in such a way that it contained enough diastatic enzymes that when used for brewing the starch it contained would convert to sugar without having to add anything else to help this process. This meant brown beers could be made from 100% brown malt. In 1770 James Baverstock used a saccharometer to show that brown malt provided much less sugar than pale malt. This caused the popularity of brown malt to decline and how beers were made changed. Nowadays brown, and even black, beers are made mainly from pale malt, with small amounts of darker malts proving most of the colour. Brown malt is still made today but by a different method and it does not contain any enzymes so it is not possible to make a beer using 100% modern brown malt.

When I got let loose on the maltings at work I diverted a small amount of unkilned green malt I'd made to try producing the historic type of brown malt. I'd looked at an old malting text book to see the sort of temperatures and times that were used when kilning brown malt, but sadly I didn't look closely enough. I put the still wet grains into a hot kiln despite knowing that moist heat would be more damaging to the enzymes. I hoped they might undergo something similar to the in grain mashing of crystal malt, before drying out and leaving a sweet and enzymic brown grain.The samples I tasted during the kilning did indeed get sweeter, but by the time the grains had dried and developed colour the enzymes were well and truly knackered. When I tried mashing them stayed resolutely starchy.

Looking more closely at Stopes I saw that before grains were kilned they were pre-dried, a process called "withering", which I have since seen mentioned in a contemporary text book. Basically, when kilning malt you have to heat it gently when it's moist and only when it's had most of the moisture driven off can the temperature be increased to the point that colour will develop. Thought things were done differently in Stopes day the first part of this process is still called withering by some.

Somewhat disheartened by my failure I tried again by baking some lager malt in the oven at home. Lager malt is the least kilned and most enzymic malt I had to hand, which I thought would be closest to withered but unkilned malt. References to old fashioned brown malt also call it "snap malt" due to the sound it made during kilning, or "blown malt" due to the way the kilning made the grain swell up, perhaps like torrified wheat.

When the malt was baking I could certainly hear it snapping, but the amount the grains swelled in size looked minimal. Once a suitable brown colour had been reached I stopped baking and tried making a mini-mash. Even more dishearteningly this was also a complete failure.

I knew the damn stuff could be made so I sat back for a re-think, and looked again at some correspondence I'd had with Ben Heaven*, someone Ron Pattinson had put me in touch with, who had already successfully made diastatic brown malt.

The path to my salvation lay in re-reading something I'd already been told: there were different types of historic brown malt. In the 1700s it would have been diastatic but by the 1800s when Stopes book was written it was probably not. With this information I decided to forget trying to follow Stopes instructions and simply see what was the brownest malt I could make that would still have enough enzymes left to break starch down to sugar.

I tried to bring a bit of scientific rigour to this process and devised a simple malt baking experiment. I baked lager malt at 200°C and after 30 minutes started taking 50g samples every five minutes. Not having a mill to hand I had to crush these using a rolling pin which was a tedious business I have to say.

50g of malt after crushing
More mini-mashes were made in a thermos flask:

I used a 3:1 liquor to grist ratio, preheated the flask with boiling water and mashed at 64°C. To ensure maximum time for starch conversion I then left the flask over night before testing for starch. 

On with the iodine

My experiment revealed that 45 minutes was the limit to which I could bake to and still get starch conversion. Even then it was right on the edge and though no blue black colour was made there still seem to be some colour development. When analysed the malt had a colour of 80 EBC, which puts it as darker than modern amber malt, but paler than modern brown malt. This sounds about right for a diastatic brown malt, as I'd already found roasting malt until it's the colour of modern brown malt destroys all the enzymes.

After I'd finished my experiment I noticed that I could have saved myself a lot of effort. Two publications I already owned, Old British Beers and How to Make Them and Radical Brewing both contain pretty much the figures I'd found for making brown malt. Oh what an ass I am.

Having worked out the conditions for creating my malt I needed to scale up production. I'd read brown malt was kilned with a shallow bed depth so I made a crude shallow wire tray. It was a bit of a bodge job but I was getting impatient by this point.

The tray would hold about 2kg of malt so it took a few goes to make enough malt to brew with, as I wanted enough to make a strong beer. To save on wasting electricity over a series of weeks I baked a tray of malt every time I had a spud in the oven. I'm sure I had a photo of the baked malt somewhere but I can't find the damn thing, so I'll get straight to the brewing. Here's a picture of the mash after a bit of recirculation:

The wort was suitably brown and had cleared which was a good sign (when wort is still starchy it stays opaque)

Then it was on with the boil, plenty of Goldings, England's oldest hop variety, added. I consulted Ron's proper book to find a suitable hopping rate.

Rolling boil

I managed to get a gravity of 1.073:

As other brewers had found all those years ago the mash efficiency was much lower than for pale malt based beers. I've not yet worked out the efficiency I get with my current mash tun, but extract was at least 20% down on what I get with normal ingredients.

The fermentation started well but stopped much sooner than normal, so low fermentability as well as low extract. I can see why this malt stopped being made. The poor fermentability did mean that the beer has the sweetness I was hoping for back when I was wondering if some sort of crystallisation occurred in the making of this malt. There was also of course a lot of roasty flavour to the beer, but not a lot of the astringency you get from the highly roasted modern malts used in modern porters and stouts.

To try and get the gravity down a bit further I added a culture of Brettanomyces claussenii after primary fermentation. It's highly likely Brett would have helped ferment historic stouts and porters. It certainly helped to beer dry out a bit, and then lead to my bottles over carbonating. Ho hum.

I can't detect any Brett flavour in the beer, it must be over powered by all the roastiness from the malt. The taste of the beer is certainly similar to the beer made with 40% modern brown malt by Head in the Hat brewery, but I can't think of any other commercial beer like it. It's a pleasant enough drink but it's not the tastiest stout (or is it a porter?) I've drunk. Dare I say it it's one for interest only.

I've currently got another batch sitting in a fermenter to which I added a mixed culture. I'm going to leave that one a year before trying it, which if nothing else will again be interesting.

I'd like to have another go at making diastatic brown malt from scratch instead of using lager malt as a starting point. Sadly I don't have "muck around with things that interest you but have little practical value" in my job description so I haven't had a chance yet. Still, my annual appraisal is coming up so maybe my boss can be persuaded to allow this vital change.


* Ben has now set up his own brewery: Bondgate Brewery. It looks like it's on a very small scale but I see from the webite that limited edition beers made using historic ingredients are released occasionally, so those of you who can't get to the Florence or brew your own might still have a chance to drink historic style porters or stouts.


  1. Good work Ed, I would persist in this. There should be a "sweet spot" where the beer acquires a good palate particularly at its circa-6% ABV range of the 1700's. This would require as well 6-12 months aging in wood, ideally. I can't find it now but I definitely remember reading an article of around 1800 which advised to put about 20% of pale malt in. This may have been the start of the time when pale finally dominated the mash but I'd guess expedients in the field so to speak were always used of this nature, and it might help the mash. Otherwise, with the reduced efficiency of the mashes, you will want to make them as rich as possible to get as a gravity as you can. Perfect Pint in the U.S. has successfully made his own brown malt and porter from it, I can point you to this if you don't know it.


  2. Well done, Ed.

    Some of Ben's beers made with various types of brown malt turned out very well. And quite unlike modern beers.

  3. It's definitely unlike modern beers! I'm aiming to get to your do in London on the 28th, I'll bring you a bottle then.

  4. Fascinating, Ed - "extract was at least 20% down on what I get with normal ingredients" - that sounds about right. I strongly suspect Gary is correct, and some ageing – perhaps six months – is going to be required to get a more acceptable flavour on the beer. You couldn't persuade your employer to let you build a 20ft high 3,000-barrel vat, by any chance?

  5. Great experiment and an excellent read. I will be trying my hand at making some of my own in June some time and hopefully can replicate or better your results. Thanks again.