Dear Mr. Wizard,

I have talked to some friends about building a RIMS unit into my newly purchased MiniMash system. The reason I want to add this component is because I’m not able to hit my strike temperature consistently (as I don’t know the mash tun thermal mass, even after contacting the manufacturer). They say to just pre-heat the tun with hot water and the thermal mass will be zero. They are discouraging me from adding this equipment for the following reasons: extra expense, more equipment to clean and maintain, more time required to mash and more complications hitting mash temperatures when compared to infusion mashing. When they talk of commercial breweries, however, they say that everyone vorlaufs in order to hit mash temperatures and clarify wort. Isn’t that the same thing as incorporating a RIMS? I’m just looking to have better control over the mash temperatures and RIMS has to be easier than step mashing with additions of hot water, right?

JC Converse
Aliso Viejo, California

Mr. Wizard replies:

I must confess that I am one of those particular brewers who likes nailing my target temperature and appreciate the gadgets of modern brewing. I have a mash mixer where I work that is externally heated with steam and we have a computer system that automatically controls the mashing sequence. We even have some programming code to calculate how hot the mash water needs to be in order to hit our strike temperature depending on the malt temperature and our chosen ratio of water to grist. I do not believe, however, that this type of precision and accuracy is required for brewing great beer. It simply makes consistency easier when consistency is important.

In our brewery we do not use the recirculating infusion mash system (RIMS) for mash heating, but we do vorlauf. These two terms do not mean the same thing. Vorlauf is the first step of wort collection (one translation of vorlauf into English is “forerun”) and serves two purposes — hitting mash temperature is not one of them.

The vorlauf removes weak wort from the under-plate area of a lauter tun and returns this weak wort to the top of the grain bed. Strictly speaking, a lauter tun is only used for wort separation and is filled with mash after mashing has occurred. The false bottom of a lauter tun is covered with water before filling and that is why there is weak wort in the under-plate area. The vorlauf also helps clarify the wort before sending it off to the kettle. Most commercial brewers vorlauf for about 20 minutes and this time permits about 40% of the liquid in the mash to be recirculated.

The RIMS just happens to recirculate wort from the infusion mash tun (combination mash and lauter vessel) continuously during mashing to move the wort through an in-line heater. The primary objective of this recirculation is to heat the wort and wort clarification is simply an unintended bonus.

There is no doubt that a RIMS retrofit will add the features you desire. You can also do step mashing by adding known volumes of hot water provided you hone your technique, collect data and accurately measure your ingredients. I am not surprised that the manufacturer of your brewing rig does not know its thermal mass, but if you know how to deal with that variable in a calculation, you also know how to determine it empirically. Some engineers consider this to be a miscellaneous heat loss term and add a loss term into their energy balances.

In layman’s terms, if you use room temperature malt and determine the water temperature needs to be 162 ºF (72 ºC) to hit a mash temperature of 150 ºF (66 ºC) and you come in at 148 ºF (64 ºC), use hotter water the next time around. As long as your malt and mash tun are at room temperature (or your mash tun is always pre-heated to some temperature) and you know the ratio between water and malt you can empirically determine an off-set. My rule of thumb for infusion is to add 12 ºF (7 ºC) to the desired mash temperature to determine water temperature. This assumes a 3:1 ratio between malt and water and that the malt is at 68 ºF (20 ºC).

Once you have a single infusion dialed in you can begin to develop your method of adding hot water to increase mash temperature. Again, the key is keeping good records and measuring the amount you are adding. Brewers in Europe used decoction mashing long before the advent of thermometers and many argue that consistency was one of the reasons.

A word of advice on thermometers is to have little faith in their accuracy, especially if they are the bi-metallic type with a dial indicator. I strongly recommend periodically measuring the temperature of an ice bath and the temperature of boiling water. Your thermometer should read 32 ºF (O ºC) and 212 ºF (100 ºC) respectively. If it does not, adjust the calibration screw on the dial or rotate the dial face by using the nut on the stem to make the thermometer read properly in the ice bath (an ice bath temperature is not subject to changes in atmospheric pressure like the temperature of boiling water). It’s your choice, but if I had just bought some new brewing equipment I would try to fine-tune my method before modifying the design.