How we make Pet-Nat: frequently asked questions (and some math)

We’ve been making Pet-Nat for a few years now. Since the beginning there has been a huge interest how it’s done and so I thought it’ll make sense sharing our experiences and describing how I currently do it in a blog post.

From the beginning on our goal was to end up with a pressure of 2,5 bar to match the German definition of a semi-sparkling wine (“Perlwein”). And because we like these kind of bubbles. Reaching these 2,5 bars is not that simple and involves a little bit of math. And most importantly: pure juice from healthy soil.

In the beginning there is a simple formula: 4g of sugar make 1 bar. But actually, it’s not that simple. If you try it that way you’ll always end up with a much higher pressure. It drove me crazy. For years. Until I realized: the juice is still fermenting so … it produces CO2 and of course it does have bubbles already! If you put fermenting juice in a sparkling wine bottle and measure the pressure it can easily reach 1 bar. So: if I want to achieve 2,5 bar in the bottle I will measure the pressure of the fermenting juice first. Let’s say it’s 1 bar. So I just need 1,5 bar in addition which equals to just 6g of sugar. If I want to disgorge I’ll go up by a little less than one bar so maybe 3g of sugar. I disgorge warmly so I loose quite a bit of pressure doing that.

After bottling the bottles will lie in boxes until they have finished fermentation. Then we’ll turn the bottles upside down. Sometimes there can be big (and long) chunks of tartar which are hard to impossible to remove by disgorging. In this case we’ll break them by giving the bottles a decent shake before turning them upside down. It will take a couple of months till the bubbles have integrated making them finer and more stable. From that point on the Pet-Nat can either be disgorged or aged longer.

When it comes to disgorging there are obviously many set-ups possible. I disgorge warmly so noch freezing or chilling and no machines. Simple craftsmanship. Here is a video showing you how we currently do it:

 

It’s a simple set-up. I disgorge into a tank that we call “washing machine” – it’s very convenient for that purpose. The yeast leaves the the tank via a short hose connected to the bottom of the tank. We rack the leftovers the next day and then again after a couple of days, it makes a decent wine for blending. The next step defines the final pressure by replacing a defined amount of Pet-Nat with still wine. Here is how the math works. Let’s say we have our finished Pet-Nat with 3,5 bars and a still wine with 0 bars. The 3,5 bar refer to a disgorged bottle though – you’ll loose quite a bit of pressure while disgorging! To calculate our target pressure which is 2,5 bars we use the well known blending cross:

This way you can simply calculate how many parts of sparkling and still wine you need to achieve your goal. The rest is simple: Having 3,5 parts in total and a 75cl bottle 1 part = 75/3,5 = 21cl so you need 21cl of still wine with 0 bar and 2,5 x 21cl = 54cl sparkling wine with 3,5 bar to achieve 2,5 bar total.

You can use a different wine to make a blend or the same wine in a non-sparkling version and put the leftovers back in the tank. Many options, no waste. Take care though to empty all bottles the same way as you will loose more or less pressure depending how foamy the Pet-Nat gets when you pour it from the bottle to a bin.

We use a simple bottling machine to top up the bottles. It’s quicker than doing it by hand and all bottles will be equally full. After that we just close the bottles, clean them and let them dry for labelling.

I hope this answers some of the questions out there. Let me know if I got something wrong, if you know another trick or if I missed out on anything!

  9 Replies to “How we make Pet-Nat: frequently asked questions (and some math)”

  1. Hayley
    October 10, 2019 at 10:06

    Hi. Great information and video. Thank you for sharing. I’m currently attempting to make a sparkling rosè “pet nat” style at home. (I have about 50 litres fermenting in the barrel as I write this) It’s my first time and I think I’m in way over my head but there’s no turning back now…. which type of bottles do you use? Champagne? Normal wine or beer bottles??? Please help

    • October 10, 2019 at 10:16

      Champagne / sparkling wine bottles! They can resist 10 bars of pressure.

      • Hayley
        October 10, 2019 at 15:01

        Thank you for your quick reply. Much appreciated.

  2. Alex
    January 6, 2020 at 06:13

    Hi, this is a great description of the pet nat making process. I am also attempting to make pet nat at home and have a question. I bottled the wine at around 2.1 brix them stored them neck down. After two weeks I noticed they had quite a bit of sediment so I decided to disgorge them. The sediment cleared well and rebottled the wine and capped them. I lost a fair amount of pressure however there is still 1.5 Brix of sugar. My question is do you think the wine will continue fermenting to rebuild the desired pressure?

    • January 6, 2020 at 10:42

      There is no way I can answer this question. I don’t know your juice, the strength of the yeasts and the nutrition situation. But by disgorging you removed most of the yeasts so it’s going to be a lot harder now for fermentation to finish. You shouldn’t disgorge so early. Be patient.

  3. Jamie
    March 10, 2020 at 04:58

    Hi! Nice little write up, cheers 🙂 I’m currently making some Viognier Pet Nat and wondering at what brix to bottle. I’ve heard anywhere from 5 – 0.25… Any pointers for beginners? I don’t think i’ll disgorge as I don’t mind a bit of sediment!

    • March 25, 2020 at 13:23

      Brix measures density. You need grams of sugar per liter, likely measured by a lab if you don’t have the equipment to measure it yourself. Everything else you can read above.

  4. Henry Laas
    March 10, 2020 at 06:33

    Hi! GREAT video. I have a question. I want to ferment wine down to a brix that will give me 3-4 volumes of gas.
    If I assume there is about 0.8-1.0 volumes in the fermenting wine, at what brix should I bottle? I would like not to add any sugar.

    • March 25, 2020 at 13:21

      I don’t know what a “volume of gas” is in bar. Sorry but you have to google that yourself 😉

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