Low Original Gravity - Possible Causes?

[Coxy]

Hi all, it's been a while since I've been on here but I've just gotten back into brewing recently after being overseas for a few years. My experienced mate walked me through doing a partial mash (APA) about a month ago (I had previously only done DME/specialty grain) and all went well. I decided to give it a go without his help on Sunday and I must have stuffed it up a bit because my OG was much lower than anticipated (1.032 instead of 1.046). I'll give my recipe and a brief description of my equipment and process. Any help here is much appreciated.

Recipe:
2kg Base Malt
0.2kg Crystal Medium
0.88kg DME (saved a bit from the 1kg to use for priming sugar)
17g Magnum (14.7%) Hops for 60min
8g Cascade (6.9%) Hops for last 15min
30g Cascade Dry Hop (not added yet)
American Ale Yeast (1056)

Equipment & Process:
I'm using a 5Gal (19L) cylindrical cooler for a mash tun. I heated up 6.6L (3L/kg) of water to about 74C before adding to the tun and left it for about 2-3 minutes before checking temperature drop due to the cooler absorbing heat. Temp was about 70C so I added about 500mL of boiling water to bring it up to 72C which was my calculated strike temperature. I measured the temperature about 1 minute after striking and hit it spot on at 67C which was my target. I then left it in for 60 minutes (without checking temp), and to my disgust it had dropped to 60C over the hour. I then sparged with about 3.5L of water at about 80C into my 13L boil pot, added the wort out of the mash tun to the pot and topped it up with boiling water before doing my boil. Hot break was visible during boil. The wort was chilled in an esky full of icy water after the boil with a good cold break. Once wort had cooled down to about 25C, I tipped it into the fermenter, aerated it with a good stir, topped it up to 20L and put it in my brewing fridge until it cooled to 19C for pitching.

SG reading was 1.032, much lower than the intended 1046.

What are the possible causes of such a low SG? I will give my thoughts on the cause and invite any comments/help/suggestions on my process.

Causes (my thoughts):
1. I think that I needed to put the water into the mash tun at a much higher temperature (say 77) and let it cool to strike temp over about 10-15 minutes. This would ensure that the cooler had absorbed all the heat it had intended to, resulting in less of a temperature drop over 60 minutes.
2. I should have checked my mash temperature after it had been in for 10-15 minutes and added some near-boiling water if necessary. While not as good as full temperature control on the mash, it would be better than letting it get too low.
3. I could have sparged with another 2L or so of water, as I had to top the pot up anyway for the boil. This may have got out more of the fermentables into the pot.

Edit: Sorry, I should have mentioned that I'm just using a bag in the tun, so don't have a lautering set up (just sparged by pouring hot water over the bag)

 

[mxd]

how did you make your recipe ?


are you trying to use .88 KG of DME and 2kg of grain for 20 ltrs @ 1.046 ?

 

[dicko]

It appears that you don't have enough fermentables to make 20 litres of 1.046 beer.

 

[TheWiggman]

Looking at your grain bill you may only have enough fermentables to produce an SG of 1.032 for a 20l batch. Adding additional water (rather than through sparge) will drop your gravity as well. The high mash temp to start with will keep it a bit lower but seeing as the temp dropped this would have helped to increase the gravity over the hour.

What have you used to work out your recipe? Maybe there's a software setting that's giving you misleading figures?

 

[Coxy]

how did you make your recipe ?


are you trying to use .88 KG of DME and 2kg of grain for 20 ltrs @ 1.046 ?

Recipe was done up in an iPad app called BrewPal, but was basically a modification of a partial recipe in the Brewing Classic Styles which used 1kg of base malt, 0.114kg crystal and 2kg light DME and slightly different hop additions. All I did was swap out 1kg of the light DME and substituted it with an extra 1.1kg of grain. The app had an expected OG of 1.045 (sorry was just out in earlier post), but I have just realised that I had the 'efficiency' of the mash set to 90%, when I gather it should probably be set to something more like 70 considering that I don't have a full lautering set up.

What have you used to work out your recipe? Maybe there's a software setting that's giving you misleading figures?

Indeed, I think you are correct - mash efficiency was set to 90%. What do you think is a reasonable setting here?

Thank you all for your speedy replies

 

[brouhaha]

I'm certainly no expert, but I would think you'd need to swap something like 2.5kg of grain for 1kg of DME.

 

[GalBrew]

Indeed, I think you are correct - mash efficiency was set to 90%.

There is your problem, wind it back to at least 70% until you work out your actual efficiency. Or alter your efficiency in your recipe until your expected OG reaches your actual OG, will give you an idea of what your efficiency was.

 

[Coxy]

Well, hopefully most of the sugars in it are fermentable and it gets down to 1.008 or lower so at least I get 3% abv or so and it won't be a total waste of time.

 

[Scooby Tha Newbie]

To get that OG (1045) I need to use 3.4-3.8 kg of grain. Your mash Efficienty would be reasonable at 70-85%. 85% I think you would be very happy. I would lol.

 

[jzabski]

Yup no where near enough grain, shame u will have a watery mid strength. maybe save it for your mates that drink middies.

 

[mxd]

it aint dead add another 2.5 kg of dme (which will be about 1.50 ish at 20 ltrs, with your 1.032 should average out at 1.40 ish)

 

[Scooby Tha Newbie]

it aint dead add another 2.5 kg of dme (which will be about 1.50 ish at 20 ltrs, with your 1.032 should average out at 1.40 ish)

+1 if it was me I would boil up the dme (1.5kg) and add some hops. Let that cool then add to fermenter. Maybe even secondary that way there would be less mess and a great beer.

 

[Coxy]

it aint dead add another 2.5 kg of dme (which will be about 1.50 ish at 20 ltrs, with your 1.032 should average out at 1.40 ish)

Great, thanks for the advice! I think I will definitely do this.

My app says that adding 1kg of dme would bring it up to 1.045 (adjusting for the increased overall volume going up to 21.5L after dissolving it in a bit of boiling water) - I'm not sure what you mean by 2.5kg would be 1.50ish?

Edit: Oh, I think you meant 1.050ish(?) - I think I may just dissolve another 1kg of DME and add it in for extra fermentables. I don't think boiling it up with hops would be necessary as it will have the bitterness it needs already (will lose a little bitterness as volume increases 7.5%, but not too much) and I will just adjust dry hop for aroma.

 

[Scooby Tha Newbie]

Yes mate sorry not very clear I ment boil your DME then add hops for aroma. If you cooled it fast it shouldn't add to much bittering.

 

[Ducatiboy stu]

Dont raise yourstrike water temp. If you got 67*c after adding grain you are bang on. A temp drop down to 60*c is not such a bad thing ( not ideal but not the end of the world ). Most good modern malts will convert in 20mins.

 

[Coxy]

Dont raise yourstrike water temp. If you got 67*c after adding grain you are bang on. A temp drop down to 60*c is not such a bad thing ( not ideal but not the end of the world ). Most good modern malts will convert in 20mins.

Yep, thanks. I wasn't planning to strike at a higher temp. Rather, I was going to put it into the cooler at a higher temperature and let it cool down for however long (10-15 mins) it needs until it reaches strike temp. This way, the cooler will absorb the heat that it needs to and won't still be absorbing heat (and dropping temp) after I strike. I think I did not allow the coolertun to heat up enough before I added my grains. This is probably a minor issue as you say, however, and it would seem that simply calculating the right amount of fermentables is my main issue here.

 

[mxd]

I did get my arithmetic wrong , but you got the idea

Use your tool not my mad cow brain (my rested brain now calculates to 1kg of DME)