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]
