Brewing experiment: How low can you go?

I’ve often wondered how much influence one can have on the fermentability of wort using the mash temperature.

Most beers are mashed at 67°C/152°F, it is an all-around mashing temperature. But sometimes I’ve seen people state that they mashed on the high side 69°C/156°F or on the low side 65°C/149°F and I’ve wondered: Does a change of 2°C/4°F really matter that much for the fermentability?

I had the urge to brew but didn’t know what to brew. I therefore decided just to brew to explore this, although approaching it from another angle: How low can I go in final gravity? How fermentable can I make my wort?

Brew day

I had a random collection of leftover hops in my fridge that I decided to use together with 4kg (8.8 lbs) of Maris Otter malt to make a 20 liter (5 gallon) batch.

When setting the brew up in BeerSmith to get a feeling for what I could expect in OG/FG I came across a multi step mashing profile called Pilsner step mash, designed to maximize fermentability. I decided to use it for my experiment. It is described in BeerSmith as:

This is a pilsner mash profile that can be used for styles requiring high attenuation and/or modification.

The temperature profile of the wort during the mash is shown below. Doing multi step mashing is very easy on my system and require little effort, thanks to my software for controlling my electric BIAB system with recirculation.

The mashing profile of the “How Low Can You Go” brew. The total mash time was just under 2,5 hours in 4 steps: Acid rest at 37°C, protein rest at 52°C, first saccarification rest at 63°C and second saccarification rest at 72°C ending with a mashout/heat to boil and pulling the BIAB bag out at 2,5 hours after mashing started.

BeerSmith predicted an OG of 1.047 and FG of 1.006 for 4kg of Maris Otter in my system (21 liters expected into fermenter).  After mashing (no sparge, BIAB system) I got an SG of 1.040 and a preboil volume of about 24.5 liters. I then boiled for 60 minutes before cooling using an immersion chiller and whirlpooling.

Measured OG after boil was a surprising 1.050. The extended step mash had given great efficiency.

Cooled wort was put into fermenter and allowed to stabilize with the ambient temperature (or while I cooked dinner).



I then pitched a pack of the Belle Saison yeast from Lallemand after rehydrating it according to the instructions in the yeast datasheet.20180211_203212.jpg

I choose this yeast both out of curiosity, because I did not have space in my fermentation fridge to do a below indoors ambient temperature fermentation and because it has a reputation for being a good in attenuating, maching with my goal of this experimental brew: How low can you go.

My fermentation is a plastic bucket that I’ve added a thermowell to. The thermowell is inserted through the lid using a fermentation lock grommet. The thermowell extends into the middle of the bucket, well submerged in the wort. In the thermowell I have a DS18B20 temperature sensor. This is hooked up to a Raspberry Pi controller running my tfbrew software, now configured for fermentation logging (and controlling when in a fridge).

The fermentation started only few hours after pitching the yeast and was completed in 3 days.

Since the fermentation temperature was not controlled by placing the bucket in my fermentation fridge this was an opportunity to observe how the temperature of the wort would change as the fermentation progressed. The metabolism of the yeast generates heat as it chews through the sugars in the wort. How much I’ve never measured before now. The fermentation started just below 20°C, rose to almost 22°C at the peak activity and fell again below 20°C once fermentation was done. This can be seen on the plot below.

The plot also shows the estimated SG of the wort as the fermentation progressed. I have a wireless Tilt hydrometer in the bucket that the Raspberry Pi controller is reading the gravity estimation from in real time.


Some very interesting things can be seen from the plot

  1. The fermentation takes only 3 days to complete.
  2. The wort must have been super fermentable, going down to 1.000 sg from 1.047sg (as measured by the Tilt, not fg not yet verified by a traditional hydrometer)
  3. The temperature of the wort increases by 2°C (3-4°F) during fermentation.



It is apparenty possible to go make wort highly fermentable and go lower in final gravity than I thought. Traditionally when fermenting beers of this “size” using the common 67°C (152°F) mashing temperature I would have expected the FG to be about 1.008.

Any good experiment should raise new questions. This one does for sure:

  1. How much of the attenuation comes from the yeast? Would I get the same FG with a Chico strain yeast (US-05, wy1056) or Lallemand Nottingham? I’ve never totally understood how why some yeasts should attenuate less than others in low or moderate gravity beers. The stress on the yeast shouldn’t be too much. Or do some strains just prefer to leave unfermented sugars? (Not likely)
  2. How much of the fermentability of the wort is a result of the multi step mash with low mash temperatures and how much is just a result of the long time the enzymes were allowed to chop up the starch? Could I get the same result with a 2-3 hour mash at 67°C? Is this the trick to well attenuated high gravity beers such as a Barleywine?

I’ll report back on this brew in 1-2 weeks when I have it kegged.


Recipe from BeerSmith

BeerSmith 2 Recipe Printout -
Recipe: HowLowCanYouGo
Brewer: TF3HR
Asst Brewer: 
Style: Saison
TYPE: All Grain
Taste: (30.0) 

Recipe Specifications
Boil Size: 24.87 l
Post Boil Volume: 21.87 l
Batch Size (fermenter): 20.00 l   
Bottling Volume: 18.00 l
Estimated OG: 1.046 SG
Estimated Color: 8.6 EBC
Estimated IBU: 31.4 IBUs
Brewhouse Efficiency: 72.00 %
Est Mash Efficiency: 75.6 %
Boil Time: 60 Minutes

Amt                   Name                                     Type          #        %/IBU         
8.00 g                Calcium Chloride (Mash 60.0 mins)        Water Agent   1        -             
5.00 g                Gypsum (Calcium Sulfate) (Mash 60.0 mins Water Agent   2        -             
4.00 g                Epsom Salt (MgSO4) (Mash 60.0 mins)      Water Agent   3        -             
4.00 kg               Pale Malt, Maris Otter (5.9 EBC)         Grain         4        100.0 %       
5.00 g                Columbus (Tomahawk) [14.00 %] - Boil 60. Hop           5        9.5 IBUs      
30.00 g               Cascade [5.50 %] - Boil 0.0 min          Hop           6        4.0 IBUs      
30.00 g               Chinook [13.00 %] - Boil 0.0 min         Hop           7        9.4 IBUs      
25.00 g               Columbus (Tomahawk) [14.00 %] - Boil 0.0 Hop           8        8.5 IBUs      
1.0 pkg               Belle Saison (Lallemand/Danstar #-)      Yeast         9        -             

Mash Schedule: TFBREW - BIAB, pilsner
Total Grain Weight: 4.00 kg
Name              Description                             Step Temperat Step Time     
Acid Rest         Add 27.32 l of water at 36.0 C          35.0 C        5 min         
Protein Rest      Heat to 52.0 C over 15 min              52.0 C        15 min        
Saccharification  Heat to 63.0 C over 11 min              63.0 C        45 min        
Saccharification  Heat to 72.0 C over 9 min               72.0 C        30 min        
Mash Out          Heat to 78.0 C over 6 min               78.0 C        10 min        

2 thoughts on “Brewing experiment: How low can you go?

  1. Just moved the fermentation bucket into my fridge to prepare for cold crashing it. Planning to keg it on saturday so starting cold crash wednesday night or thursday morning. I won’t be home to start the cold crash, I’ll be in Copenhagen. Not a problem, I can start the cold crash over the internet. I just change the target temperature of my fridge from my phone 🙂

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