RIMS and decoction don't mix!

[tootal]

Over the weekend my brewing partner and I decided to brew a zoigl. This is a beer from the communal breweries in the Bavarian region of Germany. The recipe we used was given to us by a pro who actually talked to one of the communal brewers. They do a 3 decoction mash. The hops are in the mash and get boiled for 5 minutes at each decoction. At the end of the mash the beer is not boiled, only cooled and put in fermentation. Now the pro brewer admitted that he did boil his zoigl for 5 minutes just to sanatize it since the wild bacteria of bavaria would be quite different than here.

Now since we have a RIMS system I decided to try a single decoction using half of the malt up front. The rest would be sitting at 131 degrees waiting to be raised to 148. We rested the first mash at 131, 158 and then boiled with half the hops for 15 minutes and then added it back to other second mash to 148.

The problem is that when you boil half the malt, (after draining most of the liquid), you boil the oxygen out of it. When you add it back in it doesn't want to float like our normal mash does and since we were using our RIMS the mash kept wanting to stick on us. So it all worked out in the end, we just had to stir it up once in a while but the next time we do this we will do our normal RIMS routine and just do a single decoction to raise our temps to mash out of 165.

Our sparge was slow but did not stick and we hit our numbers spot on at
l.050. So the beer should be fairly accurate but next time it should be a little less labor intensive!

I just wanted to pass along our experience to other RIMS users if you were contemplating a simular type beer.

 

[VladOfTrub]

It's too bad you had to stir it up, disrupting the filter bed. The filter bed stratifies differently in a decoction than in an infusion. Like you mentioned, the mash is deaerated and doesn't float up as much as in the infusion. Boiling hops in the decoction kettle has been around for a very long time. It's a German brewmasters trick that allows the brewer to run off the wort from the lautertun quicker without sticking the mash. The hops reduce surface tension of the mash liquid, so does boiling the mash. Lautertun false bottoms are slotted differently for decoction mashing than one used with infusion. I tri-decoction. I don't use an MLT. I use a fired mash tun along with a lautertun. I pump out of the lautertun, starting with vorlauf, then into the boiler. The lautertun is a Blichmann 20 G kettle with their slotted plate. The plate was modified for decoction. I watch the sight glass. If the liquid in the glass drops below the top of the bed by 3 inches, I slow down the run off, until the extract thins during the sparge. Then, I slowly open up the valve to full, always watching the level in the sight glass. Usually, a stuck sparge using the decoction method is rare. A lot of the protein gum is boiled away in the decoction kettle. But, it takes about 30 minutes of boiling. During the decoction boil, small starch pieces that get stuck in the husk, because the mill doesn't crush them up, burst. Getting rid of the gum and starch pieces help with running off the wort through the bed. Sometimes, it's better to go with a thinner mash to thin out the extract a little. If you decide to do another decoction. If the mash in the decoction kettle doesn't begin to convert within 15 minutes, thin it down to force conversion. Then, boil it up. The extra water will help thin the main mash when the decoction is dumped into it. A thick mash, heavy with extract can block the filter bed and stick the run off. Especially, if the run off flow rate is high and the false bottom is the standard drilled or slotted type carried by LHBS. Old grain that sat around sucking in moisture will become pastey and slack. Mash can stick from that, too.

 

[tootal]

Thanks for the explanation about the false bottom. We have a Sabco brew magic which is all about recirculation and no stirring, at all! The decoction mash was thick but the second mash was thin. Even at that the mash just sank to the bottom and turned into concrete. I actually had to take my paddle and twist it like a drill bit to break it up. When we fly sparged I broke it up one last time and let it vorlauf until clear and then ran it to the kettle. By the time we had the kettle full it was running pretty slow but since we hit our numbers I know we did get our sugars out of it.

Thanks for the reply as this was our first decoction of any kind. Even though I researched it, it obviously didn't sink in that the mash wouldn't float after boiling and in combination with a unit that's designed for a floating mash, well, if I lose my day job I now know how to make glue!