Author Topic: Rennet IMCU  (Read 2540 times)

Offline JeffHamm

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Rennet IMCU
« on: September 06, 2011, 02:25:57 AM »
Hi,

I've been doing some searching around, trying to figure out how to adjust rennet amounts based upon the ICMUs.  I've found on the forum here where Linuxboy recommend's 7-9 mls of 200 IMCU (international milk coagulating units) rennet for 100 lbs of milk.  And, milk weighs a touch more than water, so 1 litre of milk weighs between 1.03 and 1.05 kg (with full fat weighing less; cream floats).  So, 100 lbs of milk is roughly 43.7 litres (using 1.04 kg/l).

So, the recommendation would be 8 ml for 43.7 L of milk, or 1.83 ml per 10 L makes.

Presumably, if this were 100 IMCU strength rennet, then I would double it, to get 3.66 ml for 10 L, or 0.366 ml/L.  Which in turn would then become 36.6 ml/L at 1 IMCU. 

So, to figure out how much you would use with your rennet, say at 500 IMCU, simply divide the 36.6 by 500, which gives 0.07 ml/L, or 0.7 ml for a 10 L batch.

Am I understanding this correctly?  (i.e. is this how the IMCU units work?  Are they just linear transformations like this?) 

- Jeff
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Offline John (CH)

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Re: Rennet IMCU
« Reply #1 on: September 06, 2011, 05:41:05 AM »
Hi JeffHamm, I believe your math is correct and that it is a linear calculation as you have done, and that that calulation is a great starting point.

The problem is that this is the starting point as:
  • Rennet ages and slowly degrades with time, depending on how shipped and stored.
  • Rennet's effectiveness has many variables as it is dependent on i) milk's type (cow, sheep, goat etc), ii) milk's ingredients (animal feed, time in lactation cycle, antibiotics etc), iii) milk's pre-rennet treatment (skimming, raw, pasteurized, ultra pasteurized, UHT), iv) milk temperature when rennet added, v) milk pH when adding rennet (ie how much and how long you have pre-ripened with a starter culture), and vi) the strength of the curd you are trying to make which varies by cheese type.
Thus the more senior members here use the manufactureres recommended dosage as a starting point and based on experience and the Rennet Coagulation Flocculation Point Test results (this test has different floc times for different cheese types, ie more rennet and faster floc for Swiss cheeses vs less for soft cheeses like Camembert), adjust their next batch's rennet dosage rate up/down.

Hope someone else can also check your math to see how to adjust initial rennet amounts based on ICMU.

Offline linuxboy

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Re: Rennet IMCU
« Reply #2 on: September 06, 2011, 08:14:56 AM »
Yes, and ditto to everything John said. You use the calculated amount as a starting point, and then usually throughout the season as the milk changes, typically, you adjust rennet amount to compensate.

The beauty of IMCUs is that there is a known standard, so you can be very precise with your calculations as a way to try and ensure quality and consistency.
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Offline JeffHamm

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Re: Rennet IMCU
« Reply #3 on: September 06, 2011, 02:07:11 PM »
Thanks guys. 

I agree that I was dealing only with theory.  I've learned via the floc method, for example, that the manufacturer's recommendation of 0.7 ml for 10 L is too strong, so I tend to use 0.6 ml to get  a floc time in the 11-12 min rage.  What I was hoping to do, though, was at some point pick up some calf rennet, which has a IMCU of 180 (my current vegetarian one has IMCU of 750).  The calf rennet bottle listed "use between 0.2 and 0.5 ml per litre", but that's a pretty big starting range so I wanted to convert to get me closer to the plate, so to speak.  Of course, using my calculations my 750 would start me at 0.48 ml for 10 L, and I would probably have to increase for batch 2 as I think I tried 0.5 once and it was around 20 min to floc.  Still, pretty close.

Thanks again.

- Jeff
« Last Edit: September 06, 2011, 10:19:16 PM by JeffHamm »
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Offline linuxboy

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Re: Rennet IMCU
« Reply #4 on: September 06, 2011, 02:13:43 PM »
Fabulous way of doing it. Also keep in mind calf rennet may act a little differently with your milk, but the difference should not change the calculation. More so, it may up your yield a little. Anyway, I think you have it. Hope the approach works well for you
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Offline JeffHamm

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Re: Rennet IMCU
« Reply #5 on: September 06, 2011, 03:35:14 PM »
Thanks again Linuxboy!  I expect some differneces to occur when I try calf rennet.  Will be interesting to see how close I get with these calculations.

And, in case anyone else is interested, basically, if you switch rennet, and now have something with a different strength, to get an estimate of how much of your new rennet to use, do the following:

New Amount = Amount of rennet normally used X (IMCU original rennet)/(Litres of your previous makes) X (Litres of your new make)/(IMCU of your new rennet).

So, for example, if I was using 0.6 ml of 750 IMCU strength rennet for a 10 L make, and then buy this 180  IMCU strength rennet, how much should I use in my next 10 L make?

New amount = 0.6 X (750/10) X (10/180)
New amount = 2.5 mls.

And, interestingly enough, the range on the bottle was 0.2 - 0.5 ml per litre, so 2.5 for 10 Litres sounds about right.  It's also at the low end of their suggested dosage, and my use of 0.6 is less than the 0.7 marked on my current bottle (current rennet has no "range"; and 0.7 converts to 2.9 ml).

Anyway, once I actually pick up some new rennent to try this, I'll report on the results. 

- Jeff

P.S. I've put an excel work sheet that will do this calculation for you.  Also, this booklet has a page that I find very useful when having to slowly increase temperature over 30 or 40 minutes.  Just enter your temperature readings every so often to see if you're "on target" or too warm or too cool. 
« Last Edit: September 06, 2011, 10:56:13 PM by JeffHamm »
The wise do not always start out on the right path, but they do know when to change course.