Although some people might dispute this, I noticed that for certain styles decoction mashing is important for the expected results, especially for the Bavarian styles. There are many reasons for employing decoction mashes:
- Improved extract yield. This can actually cause a lighter colour (provided one doesn’t boil at 100C. A good range is 90-98C max, some go even lower for Helles). The higher yield is due to several factors:
- The decoction part passes through the diastatic-enzyme range several times
- Boiling reduces the complexity of the starch and protein (helpful with dark malts)
- Dextrination of α-amylase is more effective at higher pH (optimum 5.7) and retards β-amylase activity (optimum pH 4.7). Native starch is far too complex to be reduced by β-amylase unless α-amylase has reduced it to shorter chains which is why, even for a high-maltose extract mash, the decoction is converted at temperatures favourable to α-amylase.
- There will always be amounts of unconverted starch which is entrapped in poorly solubilised malt particles. As the decoction is heated above 75C the particles burst and their contents are absorbed into the liquid extract. This makes them available for conversion as the decoction is returned to the main mash.
- Boiling the decoction decomposes HCO3 and precipitates more Calcium Phosphate. Protein gums are also dissolved at the higher temperatures where the proteolytic enzymes then can successfully degrade dissolved gum to albuminous fractions instead of clouding the beer.
- Enhanced body and foam due to the resulting smaller proteins. Cold break (protein trub) is also dramatically decreased.
- The resulting absence of residual protein gum reduces the density of the filter-bed. This is important for recipes with high wheat contents to avoid stuck sparges.
- Boiling deoxidises the mash. Avoiding oxidation is most important when one aims to achieve bright beers. Usually the decoction is pumped from below into the mash to avoid the mixing of air into the liquid. Oxidation of the mash decreases the decomposition of β-glucans (gums) and proteins. Oxidised mashes tend to give darker beers with lesser stable taste.
Indeed, may breweries make their own malt or source under modified malt for precisely these reasons. What happens at temperature ranges below 60C is most fascinating and increasingly crucial when producing a Helles-, Oktoberfest- or Weizenbier.
For commercial brewers the constraints of decoction mashing can be considerable. I was once asked to help source a brewing plant in the UK for a friend of mine. So I did a bit of digging what is locally available (always my preferred option) and called someone who made the equipment for some very well known Micro-Breweries. Once I mentioned Helles or Weizen (Wheat beer) he literally hung up the phone on me. Maybe this wasn’t the best of manners but I can understand his frustration when it comes to deal with building these systems for large scale applications. In industry this would involve mash agitators and propeller pumps to handle the grain (ideal with variable speeds). Additionally, mash tuns need jacketed heating (usually steam) so that the grain can be drained underneath from the centre of the the vessel.
For the home-brewer, things are way simpler. Considering the amounts involved, hot grain can quite comfortably scooped from one vessel to another. Care must be taken to avoid unnecessary introduction of air and splashing. I just prefer to run the thin mash into the mash tun and have the remaining grain sit comfortably in the copper ;). This avoids unnecessary oxidation and is way less messy. Putting a skimming sieve above the mash avoids the grain from disappearing unduly.
A lot of the above information is from Noonan’s excellent book, as well as from my standard go-to work from Ludwig Narziβ who teaches at the TU-Munich in Weihenstephan. However, I am not in agreement with Noonan’s mash schedule which I find too laborious and not well suited to the well modified malts available to home brewers. Narziβ describes a schedule that caught my eye because it seems to be much better adapted to well modified malts available to home-brewers.
Double Decoction Mash Type II
In his excellent wiki page, Kai has produced a very nice writeup and a great graph illustrating this technique described in Narziβ’ textbook.
Note that this schedule is for lager beers. Wheat beers need a little bit more work in the temperature range below 55C. Here are the most important concepts:
- Mash in at 35-37C. The decoction is pulled and then converted. This takes quite a bit of time because one is actually performing a full conversion to mash-out on these contents, then a boil. However, a long rest in this temperature range won’t excessively convert the proteins. A long rest in this temperature range will lower the pH slightly and ensure better solubility of the enzymes.
- Unlike during a Hochkurz schedule, the decoction undergoes a small protein rest since the start temperature is so low. This allows for perfect conversion according to the table here.
- The first decoction is boiled for quite a long time. It has a huge volume (pretty much all the grain) and if a protein rest is necessary part of it is returned to the mash tun to raise the temperature to the required temperature (50-57C) for 10-20 minutes as necessary. This won’t consume the entire decoction though and the rest keeps on boiling. After the protein rest is complete, the remainder of the decoction is returned to the raise the temperature to 62-72C – just like with an infusion mash.
- The resulting strike temperature is the same as in single infusion mashes, and it can be steered and controlled in the same manner. I wonder whether this would not be suitable for IPA’s with highly modified malts, by dropping the protein rest entirely…
- The last decoction can be a “Läutermaische” – a “sparge mash”. Ie the thin portion of the mash run via the mash filter in the mash tun.
I’ll give it a shot soon!