Decoction Mashing: Effect of boil time

I'm planning a decoction mash and am trying to figure out how long each phase of the decoction should last.

A BYO.com article on decoction suggests slowing bringing the decoction to 155, resting at 155 for 5 minutes, then bringing the decoction to a boil, and boiling for 5 minutes.

However, many other sites suggest their own rest and boil times - anywhere from 10 to 30 minutes.

It seems like boiling the mash for 5 minutes and boiling the mash for 30 minutes would have very different results.

Does anyone know what factors go in to determining the boil and rest times of a decoction?

stoutaholic said:

Does anyone know what factors go in to determining the boil and rest times of a decoction?

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Longer boils are for darker and/or less modified malts.
I use 20 min for dark malts, 10 min for light ones.

Just to give you some perspective on that rest. It is for reducing the viscosity of the mash and ideally you hold it until conversion to get the most out of the enzymes in the decoction. That is best done with a rest at 160-165 as the a-amylase will be more active there. There is a common misconception that you should match the saccharification rest temp with that rest.

Kai

The boil time for a decoction is mostly a matter of how severe you want your decoction character to be. With a five minute boil, you will have very mild melanoidin character and color from the decoction (assuming you are dealing with typical mash ratios). With a thirty minute boil, you should have strong character.

Frankly, I've never even thought about doing a thirty minute decoction boil. I would expect that to just about dry out. I usually do around 10-15, and I don't think I've ever gone beyond 15. If I were going to stir a decoction for thirty minutes, I'd probably want a brew buddy that day!


TL

Kaiser said:

Just to give you some perspective on that rest. It is for reducing the viscosity of the mash and ideally you hold it until conversion to get the most out of the enzymes in the decoction. That is best done with a rest at 160-165 as the a-amylase will be more active there. There is a common misconception that you should match the saccharification rest temp with that rest.

Kai

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Why would you not want to match your decoction rest temp with the saccharification/dextrin rest temp of the mash? Wouldn't you want the proportion of fermentable vs. unfermentable sugars to be [roughly] the same in the decoction as in the mash? What would be a benefit (scenario) of doing otherwise?

I ask because Noonan matches these temps in NBLB. The other benefit of decoction (after the decoction rest) is accessing more starches in the decoction to make them available for the enzymes in the main mash. Noonan states this temp. borderline at 167°F (75°C), i.e. when the decoction is at or above this temp the grain "bursts" open making more starches available. What's your take on that, Kai?

As for the OPs question, one of the purposes of the decoction rest is, as Kai says, to make use of the enzymes in the decoction. I would think the time of that rest could be different for each brewer. Assuming your mash parameters affecting conversion (pH, etc.) are adequate/ideal, you should only need about 10 minutes on that rest.

As for decoction boiling times, I only boil for 5 minutes (per Noonan). After scorching my first decoction, I'm paranoid of scorching... plus all that stirring gets tiring!

menschmaschine said:

Why would you not want to match your decoction rest temp with the saccharification/dextrin rest temp of the mash? Wouldn't you want the proportion of fermentable vs. unfermentable sugars to be [roughly] the same in the decoction as in the mash? What would be a benefit (scenario) of doing otherwise?

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Why is there a need to have the decoction as fermentable as the main mash? All that you want is to convert the starches so the viscosity drops (less chance of scorching) and make use of the enzymes. You may not make much use of the b-amylase at a higher temp but just adjust the main sacc rest a little lower to compensate for that. The lower you choose the decoction rest temp the longer it takes for the mash to convert. And especially if you are using all dark Munich malt, that can take quite some time.

I ask because Noonan matches these temps in NBLB.

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I think that book should be revised. Not that what is written there is wrong. It just should focus on how lagers are brewed today and also what mash schedules can be used (including decoctions). The same applies to the fermentation part where I'd like to see more focuss on different fermentation schedules that cab be used and the pro/cons for all of them. I'd also like to see the need for slow cooling to lagering removed when you completed fermentation and maturation at primary fermentation temps or w/ a diacetyl rest.

The other benefit of decoction (after the decoction rest) is accessing more starches in the decoction to make them available for the enzymes in the main mash. Noonan states this temp. borderline at 167°F (75°C), i.e. when the decoction is at or above this temp the grain "bursts" open making more starches available. What's your take on that, Kai?

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The only thing I can think off is gelatinization of the small starch granules (starch is by weight about 90% large and 10% small granules w/ the small granules having a higher gelatinization temp). But I'd say that not until the physical actions of the boil the cell walls (especially in the less modified regions of the endosperm) are fully disrupted.

As for the OPs question, one of the purposes of the decoction rest is, as Kai says, to make use of the enzymes in the decoction. I would think the time of that rest could be different for each brewer. Assuming your mash parameters affecting conversion (pH, etc.) are adequate/ideal, you should only need about 10 minutes on that rest.

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My take on this rest is: don't stress out over it and don't put too much thought into it. Hold it in the 160s until conversion (iodine test) but you may give up after 30 min. If it isn't converted after 30 min you already have an indication that you may be having problems with the mash converting at the sacc rest as well. I noi

As for decoction boiling times, I only boil for 5 minutes (per Noonan). After scorching my first decoction, I'm paranoid of scorching... plus all that stirring gets tiring!

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I boil 5 - 45 min. 5 min for mash-out decoctions, 10-15 min for lighter beers like Maibocks and up to 45 for dark Bock biers. If you get the right decoction thickness and properly rested for conversion there is no need for constant stirring. Just don't heat as much and keep the lid on. Occasionally I like to stir to redistribute the grain in the pot.

Kai

Kai, out of curiosity where do you learn all you know about brewing? Or are German's born with the knowledge?

I ask, because you always know exactly what you are talking about no matter the topic... and I've been reading a lot of more advanced books lately and am curious for more.

z987k said:

Kai, out of curiosity where do you learn all you know about brewing? Or are German's born with the knowledge?

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No we are not born with this. As a matter of fact I didn't know much about brewing and beer styles before I came to the US. There are a number of brewing text books (German and English) that I was able to read. As well as the occasional paper on the internet and then just thinking about it and trying to find the "why" we are doing it the way we are. Brewing (technology) just fascinates me.

I ask, because you always know exactly what you are talking about no matter the topic

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That's not quite true. I don't know much about non German beer styles or the use of different hops for example.

... and I've been reading a lot of more advanced books lately and am curious for more.

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Keep reading, but with a critical mind and always as if what you are reading would matter for home brewing or not. And how much it would take to implement a particular technique.

Kai

I am looking to do my first decoction mash this week. I have a bunch of darker, more heavier beers, so I figure I could try my first lager while it is still cold out.

Here is the recipe I am thinking of, tell me if you think the mash schedule looks good for these malts. Also, I have a plactic mash/tun and don't have POLs setup so I can't directly heat the mash, but either add the water or take some wort and heat it up and place it back in.

TYPE: All Grain
Taste: (35.0)

Recipe Specifications
--------------------------
Batch Size: 5.50 gal
Boil Size: 6.92 gal
Estimated OG: 1.041 SG
Estimated Color: 4.8 SRM
Estimated IBU: 14.0 IBU
Brewhouse Efficiency: 80.00 %
Boil Time: 60 Minutes

Ingredients:
------------
Amount Item Type % or IBU
7.50 lb Pale Malt (2 Row) US (2.0 SRM) Grain 96.77 %
0.25 lb Caramel/Crystal Malt - 60L (60.0 SRM) Grain 3.23 %
0.50 oz Goldings, East Kent [5.00 %] (Dry Hop 3 dHops -
0.75 oz Tettnang [4.50 %] (60 min) Hops 12.0 IBU
0.25 oz Tettnang [4.50 %] (15 min) Hops 2.0 IBU
1 Pkgs German Lager (White Labs #WLP830) [StarterYeast-Lager


Mash Schedule: Decoction Mash, Single
Total Grain Weight: 7.75 lb
----------------------------
Decoction Mash, Single
Step Time Name Description Step Temp
35 min Protein Rest Add 15.50 qt of water at 135.3 F 130.0 F
45 min Saccharification Decoct 4.81 qt of mash and boil it 152.0 F
10 min Mash Out Heat to 168.0 F over 10 min 168.0 F

I am going to use Great Western Pale Malt and don't think it may benefit from the acid rest.

Frankly, I've never even thought about doing a thirty minute decoction boil. I would expect that to just about dry out. I usually do around 10-15, and I don't think I've ever gone beyond 15. If I were going to stir a decoction for thirty minutes, I'd probably want a brew buddy that day!

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The only decoction I've done (within the last 10 years) was a couple of weeks ago and the decoction didn't really get that awesome aroma until 15-20 minutes and it just got better from there. At 30 minutes the aroma was awesome. I barely ever stirred mine...it just didn't need it. This was as thick a decoction as I could get it but then I infused it with some hot water to get it up to sacc rest quickly (158o F)...only left it there for 15 minutes...and then up to the boil. After the infusion it was just a regular ole thick-mash decoction. I did a thin-mash decoction for mash out but only boiled to hot break.

In any case, my point was that the decoction aroma was way, way more pronounced at 30 minutes than at 15. So if that's what you're after...