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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!

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LGC083 – How to Make Cheese After the Apocalypse!

05/03/2019 By Gavin Webber 4 Comments

Back behind the microphone for another season of podcast episodes, I am looking forward to bringing you some excellent interviews. This one is no exception.

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  • LGC083 – How to Make Cheese After the Apocalypse!
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Today I caught up with Ritic (that’s his pen name) and we talked at length about how to make cheese after an Apocalypse scenario.

Here is how he pitched the interview to me.

“Dear Mr. Webber,

I’ve been a big fan of your youtube channel for a long time now, and I’ve always found you a great source of information and entertainment. You’re a youtube channel that I can listen to before bed, relaxing me enough to sleep while also keeping me interested enough that I don’t lose consciousness.

I write to you today because I’m an author and I’m doing research for a story. I was hoping that you could help me with some details.

The story is a post-apocalyptic one, about a group of individuals trying to build a society. At one point, they will be gaining a few cows as part of a trade with other survivors in exchange for medical supplies. However, they will be getting more milk than their small community can drink or make into butter, and will be faced with the problem of what to do with it. Naturally, my first thought was cheese. And so I thought of you.

I was curious about your opinions on what kind of cheese a group could make to preserve their milk, given minimal resources. I was also curious about what things could go wrong for a group of people who have to use a campfire and rudimentary equipment when making whatever cheese(s) you suggest. These people aren’t perfect, and even if one of them knows the basics of making cheese, it will be their first attempts. Further, their knowledge comes from information that they read once before the apocalypse; they’ve never actually made it themselves before now. I don’t like writing perfect people, and I find that people who make mistakes and have to struggle through them are far more interesting than people who get it right every time.

Any and all information that you might be able to give me would be greatly appreciated. Thank you for your time.

Sincerely, Ritic (my pen name) “

ASK A QUESTION FOR THE PODCAST

Don’t forget that you can leave a voicemail message that I will answer and feature during the show.  Just remember that I cannot answer them straight away, so please don’t expect an instant reply.

Support the show!

If you would like to support the podcast and YouTube channel so I can make new and interesting cheeses and cheese related content, then please support me via Patreon.

SPONSORED BY…

This podcast is sponsored by Little Green Workshops where you can pick up your cheese making kits and supplies.  We stock a large range of cheese making gear and ship to Australia and most countries throughout the world.

Until next time Curd Nerds, Keep Calm and Make Cheese!

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Filed Under: Podcast

Cheese A Day Challenge

17/02/2019 By Gavin Webber Leave a Comment

During the month of February 2019, I decided that it was high time to start tasting different cheeses from around the world and Australia that were available from my local supermarkets. A Cheese A Day Challenge if you like.

I thought that it would be an interesting experiment and broaden my cheese palate. It would also help me appreciate my own homemade cheese a lot better.

There were two conditions to the challenge that I gave myself. One, I had to eat a different style of cheese each and every day for 28 days, and two, I had to be able to source them in my town without too much effort, usually from a supermarket chain at a reasonable cost. After all, this was not going to be a sponsored challenge, I had to buy the cheese myself so as to make it as objective as possible.

I knew that a video a day may be taxing on my time, but I have managed to work out a schedule for production without too many issue.

So without further ado, here is every single video that I have produced so far and automatically gets updated as I add new challenge video each day.

Please enjoy the Cheese A Day Challenge and check out all the exciting cheese that I have managed to find. I realise that not everyone will be able to source the exact cheese that I did, but you should be able to find a suitable substitute in you region.

If you cannot see the videos below, use this link to view the playlist on YouTube.

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Day 1 Jindi Triple Cream Brie – Cheese-A-Day Challenge
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Day 2 Société Roquefort – Cheese-A-Day Challenge
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Day 3 Shaw River Buffalo Mozzarella Cheese-A-Day Challenge
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Day 4 Tasmanian Pepper Berry Cheese-A-Day Challenge
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Day 5 Maasdam Cheese-A-Day Challenge
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Day 6 Cream Cheese Cracked Pepper Cheese-A-Day Challenge
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Day 7 Meredith Dairy Marinated Goat Cheese Cheese-A-Day Challenge
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Day 8 Castello Danish Blue – Cheese A Day Challenge
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Day 9 White Stilton with Mango and Ginger Cheese A Day Challenge
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Day 10 Riverina Dairy Chilli Haloumi Cheese A Day Challenge
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Day 11 Nisi Danish Feta Cheese A Day Challenge
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Day 12 Le Dauphin Petit Double Creme Cheese A Day Challenge
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Day 13 King Island Dairy Phoques Cove Camembert Cheese A Day Challenge
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Day 14 Aldi Edam Cheese-A-Day Challenge
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Day 15 Aldi Washed Rind Cheese Cheese-A-Day Challenge
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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!

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