Rennet for Cheese Making FAQ's
After the milk has been acidified, rennet is added. This causes the proteins in the milk to form a curd and allows the liquid to separate and run off as whey. The amount of rennet used in the different cheeses varies because of specific cheese requirements. Some need a firmer curd than others and some need a longer time frame for coagulation. The curds for each cheese are different.
What is rennet?
Traditional animal rennet is an enzyme derived from the stomachs of calves, lambs or goats before they consume anything but milk. (Ours is all from calves.) It is about 90% pure chymosin.
Vegetable rennet is obtained from a type of mold (Mucur Miehei). However, even though it is derived from mold, there is no mold contained in the final product. It is an equivalent chymosin product which works equally well but is not animal derived. We have recently added organic vegetable rennet to our catalog.
Rennet thrives at temperatures in the 85-105F range, but it won't be deactivated completely until it reaches the 140F's. Rennet continues working to set the milk as long as it has the right conditions. So, when a recipe calls for cutting the curds after a certain time period, it is important to follow the directions. Otherwise, your curds may be too firm for the cheese you are trying to make.
How do I choose which rennet to use?
Rennet is standardized, so all the different kinds of rennet (liquid, tablet or powder) work the same to set milk. Liquid is the easiest to work with because you can measure it very precisely. However, the powders and tablets will keep better under more adverse conditions.
Calf rennet is considered to be the best choice for longer aged cheeses because some of its residual components help to complete the breakdown of proteins. Some of the more complex proteins in the vegetable rennet can have a slightly bitter taste after 6 months of aging.
liquid vegetable rennet is Kosher, but it has been re-packaged without Kosher supervision.
How much salt is in rennet?
The amount of salt in rennet is miniscule. It is there as a preservative. Considering that you add 1/4 teaspoon of rennet to a gallon of milk and that much of the rennet runs off with the whey during draining, the amount of salt left in the cheese is virtually impossible to measure.
If you are interested in making cheese with no salt, the fresh cheeses, Mozzarella and Ricotta are best suited for this. The aged cheeses require a slight amount of salt to sow bacterial activity.
Can I use junket tablets as a substitute for rennet?
No. Cheese rennet is 80% chymosin and 20% pepsin. Junket is 80% pepsin, so it is much weaker than cheese rennet. Even if you use more of it to compensate for this, there is so much pepsin in junket that it increases protein breakdown to the point where there are problems when the cheese ages.
Junket was made for custards. If you read the label, you will see that there are many additives in it. In spite of this, and despite the price of junket (not inexpensive), there are many recipes online for making cheese with junket. We think this originated when supplies were hard to find for home cheese making. Now that they are widely available, there is less reason to use junket.
Can I make my own rennet?
Making calf rennet used to be handed down from generation to generation. Cheese makers knew what to expect from this process. Today, some folks do make their own rennet, but the problem is figuring out how much to add to their cheese. It can take them many years to standardize the process.
Some people also make their own vegetable rennet from the juice of nettles, figs, etc. (See our blog articles,
Making Rennet From Fig Sap and More About Fig Sap “Rennet”) This seems to work for sheep's milk and soft cheeses, but not for the aged, hard cheeses.
If you make your own rennet, you will not be able to sell your cheese in the US, because regulations stipulate the use of prepared, standardized rennet.
How do I test my rennet to see if it has expired?
This is how we test our rennet: Heat one cup (8 oz) of milk to 90F. (Do not add citric acid.) Dissolve 1/4 rennet tablet (or 1/4 tsp. liquid rennet) in 1/2cup of cool, non-chlorinated water and stir well. From this diluted rennet take 2 tablespoons and add it to the milk at 90F. Stir gently from the bottom to the top for 30 seconds.
If the rennet is working, the milk surface will begin to firm or form a slight film after two minutes. After six minutes, it will have formed a curd that will hold a knife cut.
How long is my rennet good after I have diluted it in water?
You have 1/2 hour until it begins to lose effectiveness.
Are any of your rennets genetically modified (GMO)?
No. We have taken a strong stand against genetic modification.
I am having trouble monitoring the temperature of the milk after I add the rennet.
This should not be an issue, because after adding rennet, you should not be adding any more heat (there may be a few degrees of upward heat increase). Once the curds are cut, you can begin to heat while stirring very slowly. At this point, the heat will gradually transfer from the whey to the curd. (We recommend stopping the heat a degree or two before reaching the final temperature.) If you heat too rapidly, there will be a big difference between the whey and curd temperatures.
How long will liquid rennet keep in the refrigerator? Liquid rennet needs to be stored in the refrigerator. Animal rennet will last up to one year, vegetable rennet will last 4-6 months, organic vegetable rennet will last 3-4 months. After the suggest shelf life the strength will gradually drop.
Do I have to dilute it? Liquid rennet should always be diluted in non-chlorinated water before adding to your milk.
Liquid vegetable rennet is double-strength, so you will always need to use half as much as the recipe calls for.
How long will the tablets keep? Our vegetable rennet tablets will last for at least 5 years, if kept frozen. If they are not refrigerated, they will last at least one year.
How do I cut the tablets? To cut the tablets, you may use a pill cutter. Or, a quick rap on the back of a sharp knife placed on the score marks will usually work.
How do I convert the liquid amount to the tablet amount? The conversion is 1/4 teaspoon liquid rennet = 1/4 vegetable rennet tablet.
If my recipe calls for 1/8 tsp. or a few drops of liquid rennet, how do I use my tablets? If your recipe calls for 1/8 tsp. liquid, cut off 1/4 tablet, dissolve it in 1/2 cup of non-chlorinated water, and then, throw away half of it. If your recipe calls for only a few drops of liquid rennet, it will be hard to convert this to the tablets. The tablets are very difficult to measure in small amounts like this. (This is why we include rennet in the soft cheese cultures.) If you will be adding tiny amounts of rennet, it is more convenient to use the liquid rennet.
How do I decide whether to use powdered rennet or one of the other kinds? We recommend using the powder when making larger quantities of cheese. For one or two gallon batches, the liquids or tablets are much easier to measure.
How do I store it? Store in a cool, dry place, away from direct light. The ideal storage temperature is 38 to 45F. Containers should be kept closed.
Has this product been genetically modified? No. None of our rennets have been genetically modified. However, most commercial powdered rennets are GMO.
How much powder do I use? 1/3 gram (approx. 1/16 tsp) will set 2 gallons of milk for a 'normal curd.' (It is a small amount because this rennet is very concentrated.) Adjustments should be made for softer or firmer curds. Under ideal storage, the preparation displays excellent long term stability (less than 5% activity loss in 12 months). Note: There is no storage potential after hydration. It must be used immediately.