Many people undertake the HERMS or RIMS approach to brewing for the wrong reason. Let me be clear about this. The major benefits of the recirculating concept are:
1. Superior clarity of wort
2. Temperature control
3. Repeatability
Notice that "step mashing" is not in there. That is because, in my opinion, the recirculating concept is not as well suited to step mashing as other techniques such as decoction or hot water infusion. This is a no-brainer when you consider that you have to recirculate for a period of time before the mash can change temperature, but if you dump in hot water or a portion of boiled mash (decoction) and stir, the temperature increase is almost instantaneous.
I have seen several claims in the homebrewing community from brewers who say they can get "X" degrees/minute temperature rise in the mash. I'm here to tell you that these claims depend on many factors and are more than likely only telling a partial story. Let's start by setting up some ground rules for mashing in a recirculating system:
1. The desired mash or rest temperature of the wort should not be exceeded at any time. This means that wort exiting a coil or RIMS chamber should never be above whatever temperature you are trying to achieve.
2. Stirring the mash after initial dough-in is bad. If you have a recirculating system, you don't have to stir the mash. In fact, if you stir, you undo 33% of the benefits of a recirculating system. I've tried it both ways, never stirring and stirring about every 15 minutes or so and there wasn't any difference in efficiency or any other measurable parameter. The only thing that happened was that the wort that recirculated for 1 hour was noticeably clearer than wort that recirculated for only 15 minutes. DON'T STIR THE MASH!
3. You can't recirculate too fast or else you will compact the mash. In practice, I have found that about 1 gallon per minute is the maximum flow rate you can recirculate and still avoid grain bed compaction.
With these rules in place, let's talk about what happens when you do a temperature increase for the mash. Let's say you're doing a low temperature rest at 142 F and want to step up to 155 F. At this point, the wort exiting your coil is at 142 F. When the controller's set temperature in increased to 155 F, the heater comes on to heat the water. The water will continue to heat until the wort exiting the coil is at 155 F at which point it will stop heating and adjust itself to maintain that 155 F exit temperature. Let's say this takes 5 minutes. It sounds like you got 13 degrees in 5 mintues or 2.6 degrees/minute. No you didn't. What you got was a cupful of wort deposited on top of the mash bed that is at 155 F. The rest of the wort is below 155 F and needs to be recirculated through the coil in order for the entire mash to be at 155 F. In a 10 gallon batch, you can have around 8 gallons of wort in your mash. At one gallon per minute, that is an additional 8 minutes or a total of 13 minutes to raise the entire mash temperature 13 degrees. This gives a more realistic 1 degree/minute. For a 5 gallon batch, there is about half as much wort, so your time is decreased by 4 minutes which yields about 1.4 degrees per minute.
This is the reality of how temperature ramps occur. If you must have a temperature rise faster than this, your only option is to pump faster or heat the water faster. If you pump faster, I can almost guarantee that you will have problems with a compacted mash bed. If you heat the water faster, you are only saving a few minutes since the majority of the ramp time is consumed after the wort temperature at the coil exit reaches the set temperature. The entire mash has to be recirculated to achieve that desired temperature.
"So", you ask, "what about the homebrewers who are claiming they can get 4 degrees per minute?". I have the following to say:
1. They are heating wort above the set temperature and stirring the mash to speed up the process. Bad idea.
2. They are measuring the wort temperature at the coil exit and thinking that it is the temperature of the entire mash. Overlooking the obvious.
3. Their batch size is so small that the recirculation time goes quick. Misleading.
4. They are lying like fishermen. Happens all the time.
It's really as simple as that. Which is why I continually tell people that if you are building a recirculating system to do step mashing, you had better be sure that 1 to 1.5 degrees/minute will give you what you want.
Now, I must point out that for most (certainly not all) styles of beer, step mashing just isn't necessary. Today's well modified malts do not benefit from a protein rest, and in many cases can actually suffer from one. For the most part, your desired fermentable/unfermentable sugar profile can be achieved through a single temperature infusion. I know this takes all the sexiness out of it, but believe me, the temperature control that a properly built recirculating system can give you is unmatched. Add in the clarity of the recirculated wort, and the recirculating system is more than worthwhile.
Now, having said all that, I do use the HERMIT to ramp up to mash out. This is typically a temperature increase from 150 F to 168 F. I have not experienced any ill effects from a 1 degree/minute ramp in this range.
So, in conclusion, be a skeptic. If it sounds too good to be true, it probably is. Step mashing is really an advanced technique for brewers who have their fundamentals down pat. If you can't make consistently great beer with single temperature infusion, you really shouldn't attempt a step mash. Just like anything else, if you master the basics, everything else is just icing on the cake.
