Dear Mr. Wizard,
I have a question that’s been stumping me for a while. I’m an all-grain brewer and would like to try decoction mashing. All-grain brewers are always told to include a mash-out rest and to keep the mash temperature below 170 ºF (77 ºC) for risk of leaching tannins into the wort. So, how is it that a decoction mash requires part of the grist to be removed from the mash and boiled? What about the tannins?
Greensboro, North Carolina
Mr. Wizard replies:
This is a very good question that inevitably arises when knowledgeable all-grain brewers begin thinking about doing a decoction mash. The conventional rule is to mash-out at around 170 ºF (77 ºC) and not to exceed this temperature during wort collection for the reason you mention. In a traditional triple decoction mash, the mash begins at around 104 ºF (40 ºC) and a portion of the thick mash is removed, boiled and returned to increase the temperature to about 122 ºF (50 ºC). This cycle is repeated to heat the mash to 140 ºF (60 ºC) and then up to 158 ºF (70 ºC). So there are three times where a portion of the mash (always the thick mash) is removed, boiled and returned to the resting mash to provide heat.
My view on the conventional rule about keeping the temperature of infusion and step mashes below 170 ºF (77 ºC) makes sense when you consider what happens to the mash during wort separation. As the wort gravity drops, the pH of the wort flowing from a mash bed increases, and with the increase in pH, the solubility of polyphenols increase. With this, you run the risk of getting a grainy flavor if you have high pH and low gravity runnings combined with high temperature.
A decoction mash is different. Thick portions of mash are removed and boiled. The wort in mash is very concentrated, usually about 18–22 ºPlato. This means that the concentration of sugar is high. It also implies that the wort protein content is high as well since there have been no steps taken to remove protein from the wort, for example wort boiling and trub separation. During the mash boil in a decoction mash, protein from the malt reacts with tannins and precipitate. The pH is also “normal” (~5.2) at this point in time and the solubility of tannins is still relatively low compared to that seen in the last runnings from the lauter tun. I admit that the following statement is an educated guess but I would venture to bet that the reaction between protein and polyphenols is significant and explains why decocted beers are not overly astringent.
I was in attendance at a National Homebrew Conference in Baltimore 11 years ago and Dr. Klaus Zastrow, a well-known retired Brewmaster from Anheuser-Busch, was speaking about the history of lagers. After his talk I asked Dr. Zastrow the same question you asked me and he gave me a slightly different answer. He actually began by disagreeing with the premise that decocted lagers are no more astringent than other lagers (which was my premise).
I wish I spoke German, at least enough to hack by in brewing terms, because Dr. Zastrow had a specific word to describe the astringency of decocted beers and explained that this certain flavor attribute was one of the desirable hallmarks of decocted lagers. He did not imply the flavor was unpleasant but explained in English that this attribute gives the beer a certain briskness. Brisk is a tea term and is the opposite of flat or soft and I interpreted his statement to mean that decocted beers had more, uh how do you say, cojones. I hope my brief answer helps you in your quest and that this has given you the confidence to brew up a batch of that Pils with cojones you’ve read so much about!
Dear Mr. Wizard,
I’ve been doing all-grain brewing for about a year now and noticed considerable more break material in the kettle than when I was brewing with extracts. I cool with an immersion chiller and siphon directly from the kettle to the fermenter, just as I had before, stopping the siphon before drawing any break material. My all-grain batch size has been coming in typically 0.5–1 gallon (1.9–3.8 L) shy of my target volume. Then I realized, that I’m leaving that “missing wort” in the kettle mixed with the break! My question is, what’s the best way to obtain the most wort from the kettle without a lot of break?
Mr. Wizard replies:
This is really a straight-forward and easily addressed problem if you simply add a few more minutes and one additional step to your brew day — namely whirlpooling. And I’m not suggesting that you run out to the spa for a dip in a hot tub! The whirlpool method is used in nearly all commercial breweries these days to separate trub and often times pellet hops from wort in an effort to minimize wort loss. Typical wort losses in a whirlpool are less than 5% or less than 1 quart (~1 L) in a 5-gallon (19–L) batch.
Hot wort is usually whirlpooled by pumping wort out of the kettle and into a whirlpool vessel tangentially near the bottom third of the vessel. Some kettles are designed so that the kettle also serves as the whirlpool vessel (a pump and tangential inlet are installed for this purpose and the pump is later used for pumping to the wort chiller). This causes the wort to spin while trub and hop pellets collect in the center of the whirlpool. Most brewers wait for the wort to stop spinning before removing the wort from the whirlpool, either from a valve installed on the perimeter of the tank or by simply racking the wort with a racking cane.
In your case you are using an immersion chiller and these things disturb the wort currents that make the whirlpool method effective. There is nothing wrong with chilling the wort and then spinning it simply by stirring the wort with a spoon, allowing the rotation to stop and then racking to your fermenter. Since cool wort won’t kill bacteria or wild yeast, you need to be careful with the cool wort in an effort to minimize the risk of contamination. The spoon used to stir should be sanitized before use and the kettle should be covered while you wait for the wort to stop spinning.
This is an easy method and you will know if you are stirring fast enough by the way the trub settles in the center of the kettle. Commercial brewers shoot for an inlet velocity to the whirlpool of about 5 feet per second to get the desired result. If a trub pile does not form in the center of the kettle, try stirring a little faster to get the wort moving and smoothly remove the spoon while stirring so that it does not impede movement. Good luck!