Why does vegetable rennet reduce mozzarella yield?
A technical guide for cheese professionals
Many cheesemakers encounter low yields with vegetable rennet in pasta filata cheese types such as mozzarella. This article explains why and suggests ways to improve mozzarella yields and take your mozzarella yields to the next level.
What is rennet?
Let's start with the fundamentals: what is rennet and how is it used in cheesemaking? Rennet, also called rennin, is a mixture of chymosin and pepsin. Chymosin is a naturally-occurring protease enzyme that breaks down protein. This breakdown coagulates the milk, causing it to separate into curds (solids) and whey (liquid). Since ancient times, people have extracted rennet from the gastric mucosa of young mammals, including calves.
How rennet works
Milk is made up of fat globules, casein micelles, lactose, whey proteins, minerals and other components. Casein micelles are protein complexes made up of core alpha and beta casein and a hairy surface of kappa caseins. Ideally, rennet should act very specifically on these hairy kappa caseins. Breaking these down destabilizes the casein micelles. The destabilized micelles then merge to form a three-dimensional protein matrix. This protein matrix acts as a net, trapping fat globules to form curds. The more fat and protein in the curds, the higher the cheese yield. Calf chymosin is highly specific, breaking down kappa casein almost exclusively.
Why does vegetable rennet reduce mozzarella yield?
Rennets can be made from various plants, including thistle, artichoke flowers and fig leaves, which contain protease enzymes. Because these enzymes are less specific than calf chymosin, they break down other casein proteins and peptides along with kappa casein. This is known as excess proteolysis, and it negatively impacts the formation of the protein matrix. The result is that more fat and protein end up in the whey instead of the curd, directly reducing cheese yields. In essence, the curd doesn't retain as much of the milk's protein and fat because the non-specific enzymes "overcut" the curd. The high proteolytic activity of plant-derived rennets can also cause bitterness.
Slower coagulation leads to a loss of curd fines
Another factor is coagulation speed: vegetable coagulants often act more slowly than animal rennet. With tablet rennet in quick mozzarella recipes, that can lead to the curd being cut or stretched before fully setting, so curd fines wash out with the whey.
Practical tips to improve mozzarella yield with vegetable rennet
Now that we understand why vegetable rennet reduces mozzarella yield, let's explore practical strategies to optimize your cheesemaking process and get more from your milk.
- Get your milk and pH right Start with good-quality milk. Fresh, high-protein milk always yields more cheese. If you're using pasteurized or homogenized milk, consider adding a little calcium chloride (around a quarter teaspoon of 30% solution for every four liters of milk). That can help restore the milk's calcium balance for a firmer curd that retains solids better. Also remember that while a slightly higher pH at renneting (around 6.5 to 6.6) can slow coagulation a bit, it also improves curd yield by improving casein retention.
- Get your dosage right If you under-dose rennet, you'll end up with a fragile curd that breaks up. On the other hand, if you over-dose vegetable rennet you'll get excess proteolysis and all the negative impacts on yield that brings. So stick to the recommended dosage guidelines and give the rennet time to work, as explained below.
- Increase coagulation time Although many quick mozzarella recipes recommend a setting time of between five and 15 minutes, increasing this to between 30 and 45 minutes allows for vegetable rennet's slower coagulation speed. Give the milk longer to set into a firm curd before cutting or handling. This ensures the protein matrix has formed and can trap fat. Ideally, wait until the curd yields a clean break and the surface whey is clear rather than milky.
- Be gentle with the curd Remember that fine curd particles lost into whey represent lost cheese yield. Small curd cuts increase these losses, so once the curd is set, cut it into cubes of around one to two cm. Then handle them carefully. Avoid rough stirring and don't overheat or overstretch. Aim for a greenish-yellow translucent whey at draining or stretching. If you end up with a cloudy whey, you know that curd particles are escaping into the whey, reducing your yields.
- Choose a more specific rennet If you don't want to use animal rennet, both microbial rennets and fermentation-produced chymosins are good alternatives. Microbial rennets are protease enzymes produced by submerged fermentation of selected strains of fungi. While these enzymes have chymosin-like activity, they're not pure chymosin. Fermentation-produced chymosin (FPC) is also produced by fermentation but using genetically modified microorganisms. The resulting pure chymosin enzymes are structurally identical to calf chymosin for very high specificity and yields.
Take your mozzarella yields to the next level
Ready to optimize your mozzarella yields? Our biosolutions team can help you select the right rennet for your process and co-create value through improved efficiency and product quality.
Connect with us to explore how we can support your cheesemaking goals.
By Mathias Olofsen, Global Marketing and Business Development Manager for Pasta Filata
With an MSc in Food Science and Technology specializing in Dairy Science, Mathias combines technical expertise with commercial experience gained through roles at Novonesis, Chr. Hansen and Arla Unika. His background spans dairy innovation and hands-on food industry operations, giving him a well-rounded perspective on cheese technology and market needs. Connect with Mathias.
