Whey Caramel (Primost or the thicker - Mysost) Traditional Scandinavian Sweetness
This might be a winter activity as you'll need to stove on for a while, however I found that slow cookers work well too - even though the trick here is to evaporate and so the lid is off. OK - I'm writing this today on an unusual hot Bendigo day - (42c!!) so perhaps that is turning me off - however - whilst If you've never tasted whey caramel, you'll survive - it is a very delicious 'whey' of using up a byproduct.
In Norway, this spread is called primost (the softer version) or mysost (when cooked longer and firmer). It's traditionally made from cheese whey, but your living milk kefir whey makes an even more interesting version - tangy, complex, and alive with flavour. We have added a sweet miso to our whey caramel and it was - as you can probably imagine - fkg delicious.
This does feel a little witchy and alchemic because you are over a stove and turning plain whey into a deep caramel spread that's part cheese, part fudge. The lactose in the whey caramelizes as it reduces, creating rich, complex flavours that pair beautifully with everything from sourdough toast to fresh apples. Mmmmm caramel apples.....
This is a slow process - 4-8 hours of gentle cooking. But it requires minimal attention for most of that time, making it perfect for a day when you're pottering around the kitchen doing other things.
Ingredients
- 2 litres milk kefir whey (fresh is best, but refrigerated whey up to 2 weeks old works fine)
- 2-4 tablespoons cream (optional - adds smoothness)
- Pinch of sea salt (optional)
Note on whey type: This works best with whey from rennet-based cheese or from strained kefir/yoghurt. It won't work well with whey from acid-curdled cheeses like ricotta or paneer. There may not be enough lactose left after a milk kefir labneh is made, depending on how long the milk kefir was fermenting for. You can buy whey from local cheese makers.
Equipment
- Large heavy-bottomed pot (at least 4 litres)
- Wooden spoon or heat-proof spatula
- Small jars or silicone moulds
- Patience
Method
Stage 1: The long simmer (3-6 hours)
- Pour whey into your pot and bring to a boil over medium-high heat. Watch it carefully - it will foam up dramatically. Skim off the foam that rises to the top and save it in a bowl in the fridge (you'll add this back later).
- Once the initial foam is removed, reduce heat to low-medium. You want a gentle, steady simmer - not a rolling boil. The whey should be bubbling gently but not violently.
- Leave it to simmer uncovered. Stir occasionally (every 20-30 minutes) to prevent sticking. As it reduces, stir more frequently.
- The whey will gradually darken from pale yellow to golden to tan to light brown. This is the lactose caramelizing - exactly what you want.
- Continue until the volume has reduced by about 75%. You'll have roughly 500ml remaining from your original 2 litres. This stage takes 3-6 hours depending on your heat level.
Stage 2: The thickening (30 minutes - 1 hour)
- When the whey has reduced significantly and is starting to thicken, add back the chilled foam you set aside earlier. Stir it in well.
- If using cream, add it now along with a pinch of salt. This makes it richer and smoother, but it's not essential - the no-cream version is more traditional and perfectly delicious.
- Now you need to pay attention. Stir frequently as the mixture thickens. The colour will deepen further - anywhere from caramel to dark toffee depending on how long you cook it.
- For spreadable primost: Cook until it's thick enough to coat the back of a spoon but still pourable. It will firm up as it cools. This is perfect for spreading on toast or crackers.
- For sliceable mysost: Keep cooking and stirring until it's very thick and pulls away from the sides of the pot, like fudge. You'll pour this into moulds.
Stage 3: Finishing
- Once you've reached your desired consistency, remove from heat. For the smoothest texture, blend with a stick blender for 30 seconds (be careful - it's very hot).
- Cooling method matters: For smooth, creamy primost, cool it quickly. Set your pot in a sink of ice water and stir constantly with a whisk as it cools. This prevents crystallization and keeps the texture silky.
- For spreadable primost: Pour into clean jars while still warm. It will thicken as it cools.
- For sliceable mysost: Pour into lightly greased silicone moulds or a small loaf tin lined with baking paper. Leave to cool completely before unmoulding.
Alternative Methods: Low-Energy Cooking
The traditional stovetop method works beautifully but uses considerable energy over 4-8 hours. Also - we don't like having the stove on during hot days. Using a Slow Cooker or Instant Pot works too!
Slow Cooker/Crock Pot Method
This is the most hands-off approach and several makers swear by it.
The process:
- Pour whey into your slow cooker (at least 4-litre capacity). Don't fill more than half-full to allow for evaporation.
- Set to HIGH with the lid OFF. You need evaporation to happen, so the lid must stay off the entire time.
- Let it run for 22-48 hours (yes, really!). Check it occasionally - no stirring needed during this stage.
- When reduced by about 75% and starting to thicken (this could take anywhere from overnight to two full days depending on your slow cooker), transfer to a heavy pot on the stovetop for the final thickening stage.
- On the stovetop, add cream if using, and cook on low heat with constant stirring until it reaches your desired consistency.
Advantages: Very low energy use, completely hands-off until the final stage, no risk of burning during the long reduction.
Disadvantages: Takes much longer (up to 2 days), and you still need the stovetop for finishing. Some slow cookers don't get hot enough on LOW to maintain a proper simmer with the lid off - test yours first.
Tip: The whey from rennet-based cheese (rather than acid-curdled) works better - it has more milk solids and produces a smoother, creamier caramel.
Instant Pot Method
Several makers report success using the Instant Pot's sauté function.
The process:
- Pour whey into Instant Pot. Set to SAUTÉ on MEDIUM heat with lid OFF.
- Let it reduce for several hours (much faster than slow cooker, similar to stovetop). No stirring needed initially.
- When reduced by 75% and thickening, add cream and butter if using.
- Switch to SAUTÉ on MEDIUM-HIGH and stir constantly until it reaches caramel consistency.
Advantages: Faster than slow cooker, more energy-efficient than stovetop, good temperature control.
Disadvantages: Still requires several hours and attention during the final thickening stage.
THERMOMIX USERS - WE NEED YOUR HELP!
We haven't found anyone who's successfully adapted this recipe for the Thermomix. The challenge would be controlling temperature low enough for the long reduction without burning, while still allowing evaporation, and the lid must be on... so only the hole would allow for evaporation. If you experiment with this, please let me know how it goes! I'd love to add Thermomix instructions if someone cracks the code.
Which method should you choose?
- Stovetop: Best for your first attempt - you can watch and learn the process
- Slow cooker: Best for hands-off cooking if you're home anyway (perfect for winter days)
- Instant Pot: Good middle ground between speed and ease
- Thermomix: Uncharted territory - experiment at your own risk!
Important note for all methods: Whey from kefir can be quite sour and may produce a tarter result than traditional cheese whey. Some makers report this works fine, others prefer to use whey from rennet-based cheeses for a sweeter, more traditional caramel flavour. I also think that this is a great use of whey from cheese making rather than the whey from milk kefir.
Primost keeps for 4 weeks refrigerated or can be frozen for up to 6 months. Sliceable mysost can sit at room temperature for a week or two if kept in a cool spot.
How to serve
The Norwegian way: Sliced thin on dark rye bread or Norwegian flatbread, often for breakfast alongside coffee.
As a spread: On hot sourdough toast, crumpets, or English muffins. The heat melts it slightly - glorious.
With fruit: Particularly good with crisp apples, pears, or fresh figs. The sweet-tangy-savoury complexity is perfect with fruit.
On cheese boards: It's technically a cheese, so why not? Pair with sharp cheddar, nuts, and honey for an interesting contrast.
Melted: Stir a spoonful into hot porridge, drizzle over ice cream, or melt into warm apple crumble.
Straight from the jar: With a spoon. Late at night. Standing at the fridge.
Troubleshooting
It's grainy/crystallized: You either let it boil too hard early on (which can form ricotta-like curds) or didn't cool it quickly enough at the end. Still perfectly edible, just a different texture. Use the ice bath method next time.
It burnt: You needed to stir more frequently during the thickening stage. Even slight burning gives a bitter edge. Start again - this is a patient person's project.
It's too soft: Cook it longer next time, or put it back on the heat and reduce further. The "done" stage is quite forgiving.
It's too firm: You can soften firm mysost by grating it and stirring in a little cream, then reheating gently.
Why this matters
Making primost is the ultimate expression of zero-waste fermentation. You've taken milk, cultured it into kefir, strained it into labneh, and now transformed the "waste" whey into something that would cost $15-20 for a small block in a specialty store (if you could even find it).
This is traditional food culture at its finest - that sustained people through long Scandinavian winters when nothing could be wasted. Every drop had purpose, every by-product had value.
Your primost represents hours of gentle cooking, the transformation of simple sugars into complex caramel, and the continuation of techniques that are centuries old. Spread it on your morning toast and remember: this is what real food culture looks like.
RELATED RECIPES
[Milk Kefir Labneh - link]
[Whey Wild Soda - link]
[Don't Pour That Whey Down the Sink: Your Complete Guide - link]
