• About
  • Contact Me

Little Green Cheese

Cheese making at home with Gavin Webber the Cheeseman

  • Home
  • Cheese eBook
  • Podcast
  • Videos
  • Cheese Making Kits
  • Courses
  • Support Me!
  • Live!

Rennet Strength Explained

31/07/2019 By Gavin Webber 2 Comments

I was recently asked by James the following question;

I am confused on the IMCU standards, I see 200IMCU, 240IMCU, 280IMCU and I don’t understand the varying strengths and the scale of strengths. Is the higher the number stronger or lower the number? Any insight into IMCU would be greatly appreciated.

When I first started making cheese, I was also perplexed by this question. Do I just go on blind faith that the manufacturer has given me the correct instructions on the bottle? What does the acronym IMCU mean? Let’s learn more.

International Milk Clotting Unit

IMCU stands for International Milk Clotting Unit as defined in International Standard ISO 11815 (2007). It is a very technical document so I will try and break it down into a definition that a layman can understand. I like the KISS (Keep It Simple, Stupid) principle when explaining things.

Basically, one milk‐coagulating unit (U) is defined as the amount of the rennet enzyme that coagulates 10 mL of reconstituted skimmed milk powder at 30°C in 100 seconds. So how does that help us? Let’s break that down further into something we can better relate to.

Commercial rennet is available in Single, Double, and sometimes Triple strength. Rarely have I seen the IMCU/mL listed on rennet bottles that can be purchased at cheese making suppliers, but many do mention how many millilitres are required to set 8 to 10 Litres of milk. This is a good thing, right? The higher the IMCU/mL number for your rennet, the stronger it is, and you need less of it to set the same amount of milk.

From what I’ve researched, Single strength is considered to be that concentration of rennet where 200 ml is sufficient to set 1,000 kg of milk in 30 – 40 minutes at 30 – 32C. Setting time is the point where the curd will break cleanly and exude clear whey.

This differs from coagulation time which is the point where flecks of curd first appear on a spatula or slide dipped into the milk. Coagulation time is about half that of setting time, so typically, coagulation using single strength rennet requires 15-20 minutes followed by setting at 30-40 minutes.

Working It Out

So knowing that you can work out how much rennet to use for a firm set using the following calculation. If the IMCU of your rennet is 200IMCU/ml you multiply 200 x 0.01. This calculates the amount of milk in Litres that 1 millilitre of the 200IMCU rennet would set. So in this example, 1 ml would set 2 litres of milk. So to figure out how much rennet to use in 10 litres of milk you divide 10 by 2 which gives you 5. Therefore, it would take 5ml of this rennet to firmly set 10 Litres of milk at 32C in about 30 to 40 minutes.

So, if you had 280IMCU/ml rennet, then it is 280 x 0.01 = 2.8. It would take 1 ml to set 2.8 litres of milk. Once again, divide 10 by 2.8 which is 3.6. So 3.6 mL of rennet would be used to set 10 litres of milk.

Now, this is all fine and dandy, but there is another variable that throws this into confusion. The pH of the milk also affects the set time as does the amount of soluble calcium in the milk. Also, different types of cheese need different setting times. Some of my recipes state that you use 2.5 ml (1/2 teaspoon) of single strength rennet to set 10 litres and others state to use 5 ml (1 teaspoon) to set the same amount. It all depends on how acidic the milk is and if you have added Calcium chloride as to how quickly it will set.

Best Milk?

Another factor which can influence the coagulation process is the extent of pasteurization of the milk (or in other words how much the proteins in the milk have been denatured). Raw milk will coagulate faster than pasteurized milk on this basis and in the extreme, we know the dangers of using UHT milk for cheesemaking. You can learn more about the best type of cows milk to use for cheese making in this post.

Rennet Strength Explained
Checking for a clean break

Flocculation Method

Enter the Flocculation Method of determining the best curd set.

The Flocculation Method is a way to test the point of coagulation after adding the rennet to your milk.  Using a factor (determined by the type of cheese you are making), you multiply the time taken for the flocculation point to help you predict the best time for curd set.

So here is the process.

  1. After acidification time, add your rennet when the recipe states.  Start a timer so you know how many minutes have elapsed.
  2. Leave the milk for five minutes, then take a sterilised small plastic bowl and place it on the surface. It should float.
  3. Then spin the bowl gently, whereby it should rotate freely.  Do this every minute or two.
  4. You should notice that at around the 8-minute mark you may find slight resistance from the milk, test by spinning every 30 seconds.
  5. Between 10 and 15 minutes, the bowl should become ‘stuck’, indicating that the curd mass has formed.  This is the flocculation point.  It may take longer, so don’t panic.  Keep testing till the curds set.
  6. Once set, don’t try to spin the bowl any more, just remove it gently and note the time elapsed.

Watch what I mean in this video.

Now you have to multiply the flocculation point time against a factor listed in the table below. (Source: Cheese Forum Wiki)

Cheese typeFactor
Swiss & Alpine types, Parmesan, Romano2 – 2.5
Cow’s milk Cheddar2.5 – 3
Monterey jack, Caerphilly3.5
Feta & Blues4
Camembert & Brie5 – 6

The factor (normally between 2 and 6) is multiplied by the time it took to reach flocculation point, giving you the time to cut the curd.

So if flocculation time is, for example, 15 minutes, then for Parmesan, total time since adding rennet to when the cut is 37 minutes 30 seconds (15 minutes multiplied by 2.5.  So use this table to help determine the optimum time to cut the curd for the type of cheese you are making.

The Cheese Forum states;

“The reason for the different multipliers for different cheese type recipes is because the curd at time of cutting will have different strength, young curd set will more readily release water when cut versus older curd set will release less.”

A soft cheese usually has a higher flocculation time, and a larger curd cut, keeping more moisture in the cheese.

A hard cheese, on the other hand, has a lower flocculation time, and a smaller curd cut, releasing more whey for a firmer, drier cheese.

So this is why fresh cheese is moist and harder cheeses are drier!

Summary

So in summary, rennet strength is measured in IMCU but actual renneting time depends on the style of cheese that you are making and the milk you are using. Hopefully, this post has taken a little bit of the mystery out of the cheese-making process!

Will this article help someone you know? If so help them out by sharing now!

  • Click to share on Facebook (Opens in new window)
  • Click to share on Twitter (Opens in new window)
  • Click to share on Pinterest (Opens in new window)
  • Click to share on LinkedIn (Opens in new window)
  • Click to share on WhatsApp (Opens in new window)
  • Click to share on Reddit (Opens in new window)
  • Click to share on Tumblr (Opens in new window)
  • Click to email this to a friend (Opens in new window)
  • Click to print (Opens in new window)

Related

Filed Under: Uncategorized

← LGC083 – How to Make Cheese After the Apocalypse!

About Gavin Webber

Gavin Webber is passionate about home cheese making. He loves to make cheese in his spare time and shares the techniques, videos, podcasts, and recipes with his fellow curd nerds!

Learn more about him here and connect with him on Twitter, Facebook, and Google+.

Comments

  1. Martin Whenmouth says

    06/10/2019 at 14:19

    Gav, just viewed your triple jack tasting. OOOH must have been hot.. Suggest a vital ingredient is toilet paper in the fridge. Will be starting my cheese making in earnest shortly…and I’m over 70. Can’t wait!! Cheers Martin Whenmouth New Zealand

    Reply
    • Gavin Webber says

      15/10/2019 at 08:36

      Nice one Martin. Looking forward to hearing about your successes.

      Reply

Leave a comment for the Cheese Maker! Cancel reply

This site uses Akismet to reduce spam. Learn how your comment data is processed.

Follow Us via Social

FacebooktwitterpinterestrssyoutubeFacebooktwitterpinterestrssyoutube

Cheese Making Kits

Cheeseman.tv Merchandise

Cheeseman.tv Merchandise
Cool Cheesy T-shirts, sweatshirts, mugs, stickers, and more
0:00
31:28
  • LGC083 – How to Make Cheese After the Apocalypse!
Subscribe on Apple Podcasts

Archives

Tags

Aging Blue Brine Caerphilly Camembert Cheese Books Cheese Cave Cheese Press Colby Competition Cotswold Cream Cheese Drunken Cow eBook Emmentaler Equipment Farmhouse Cheddar Feta Gavin Halloumi Kits Lipase Mould Ripened Cheese Moulds Mozzarella Parmesan Podcast Queso Fresco Raw Milk Rennet Ricotta Romano Romano Pepato Salt Sanitisation Starter Cultures Stilton Storage Swiss Technique Tzafatit Video Tutorial Waxing Whey Ricotta Workshops
Online video lessons by Little Green Cheese

Subscribe to Cheese Podcast

Apple PodcastsAndroidRSS

Subscribe to Cheeseman.tv

Podcast Reviews

  • Perfect for Cheesemakers of all levels!
    by Viki Leeasa from Thailand

    I love that this podcast does not just have helpful tips and tricks on cheese making, but also stories and news from the cheese world, as well as nice little anecdotes from the host. A big fan from Thailand!

  • If you think you want to make cheese, listen to this!
    by paulsaw from United States

    Gavin Webber’s Little Green Cheese is By Far the best podcast I have ever heard! A truly informative and quality production!

  • Great program
    by p37dg9q14 from United States

    Very informative and enjoyable podcast. I started at episode 1 and currently listening to 25. I’ll be giving cheesemaking a go in the next week. Mike J from Oceanside CA

  • Great podcast
    by nicole_elias from Australia

    I have a long commute to and from work and have worked my way through the back catalogue of these podcasts. Enjoyed every one of them and hope for many more to come. Thanks Gavin! Keep up the great work. Cheers, Nicole

  • Excellent!
    by emeldridge from United States

    Looking to take up cheesemaking sometime soon and this channel has provided all the information necessary to get started!

  • Great Resource!
    by olivestones from United States

    I have been learning to make cheese for the past year. Gavin's podcast and video series has been a tremendous resource for me. His love for the cheese-making craft is evident in the amount of research he will perform in order to answer a listener's cheese question. All thumbs up for the amount of time and energy he puts into his quality podcast! ...And he cracks me up with his attempts at pronunciation!

  • Outstanding Info on Cheesemaking!
    by Sablwolf from United States

    If you are interested in anything to do with cheese, this is the podcast for you. Host Gavin Webber takes you through an aspect of cheese making, interviews with other people who are doing it, a current cheese-related news segment, and answers questions listeners have submitted in each episode. I've been quite amazed at his depth of knowledge, and he's provided answers to several problems I've encountered as well. Top rate!

  • So great!
    by jimjiminyjim from Canada

    Absolutely fantastic. My favourite cheesemaking resource out there. Listen from episode one, and by the time you’re done, you’ll have learned as much or more than you might at a professional cheesemaking intensive.

  • Fantastic podcast to compliment your YouTube videos and website
    by Paul from Brisbane from Australia

    Thanks Gavin. I have learnt a lot about cheese making from your podcasts which compliment your YouTube Videos and cheese book. Thanks

  • Super interesting!
    by Lenka S from Australia

    Gavin's podcast is so interesting and informative, he knows so much about home cheesemaking and he shares his knowledge with his listeners and answers listener questions on the show which is also extremely helpful! I am listening to them all for the second time and finding lots of new useful pieces of information. There are also interesting bits of cheese news from around the world. Thank you Gavin!

Little Green Workshops

Copyright © 2019 · Gavin Webber

loading Cancel
Post was not sent - check your email addresses!
Email check failed, please try again
Sorry, your blog cannot share posts by email.