In order to provide you with a good picture of both stages of vinegar fermentation, we’ll begin with a recipe in which we first make alcohol through the fermentation of natural sugars, then ferment that alcohol into acetic acid with the help of acetic acid bacteria (AAB).

First, brewing the alcohol. Perry is pear cider—a sparkling, lightly alcoholic beverage that’s as delicious chilled as it is warmed. There are dozens of varieties of pear; each will yield different perries and perry vinegars. In choosing the kind of pear you begin with, your guiding principle should be, Would I want to drink the juice from this pear? If the answer is yes, then by all means, rot on.

The skin of the pears hosts enough wild yeast to ferment them all on their own, but wild fermentation is always a gamble—you can never be sure what flavors will emerge, and the timeline is less predictable. This is more than fine in some cases, but since the perry will continue on to a secondary fermentation, we want a little more certainty about its flavor and alcohol content, so we’ll depend on a yeast starter. The varieties of yeast available to ferment your perry are as varied as the pears themselves. (If you start multiplying the different variables in fermentation, you’ll get a sense of just how expansive the flavor possibilities are.) Any well-stocked home-brew shop will be able to guide you to a yeast that will fare well with your pears. Stay away from baker’s yeast, which will make your perry taste, well, bready. Here at Noma, we have a penchant for saison yeast, which is actually a blend of two different strains working side by side: Brettanomyces and Saccharomyces. We find it creates a great bouquet during fermentation, with no trace of bitterness.

Equipment Notes

For the first fermentation, you’ll need a food-safe plastic bucket with a lid, airlock, and rubber stopper. You can find it at any home-brew shop. Look for a size of bucket that will hold the ingredients with about 15 percent of its volume to spare. You will also need a cider press or chinois to squeeze out the fermented liquid. You can perform the secondary fermentation in the same bucket, or use a smaller 3-liter wide-
mouthed mason jar. Either way, you’ll need cheesecloth or a clean kitchen towel, along with rubber bands to secure it to the top of the vessel. Our quick method of producing vinegar requires an air pump and air stone, which you can find at a home-brew shop or pet store. Read the recipe for full details. We recommend that all your equipment be thoroughly cleaned and sanitized.

Ingredients

  • 4 kilograms sweet, ripe pears
  • 1 packet (35 milliliters) liquid saison yeast
  • Unpasteurized pear vinegar, or another unpasteurized mild vinegar such as apple cider vinegar

The Noma Guide to FermentationThe Noma Guide to Fermentation
by René Redzepi and David Zilber

In-Depth Instructions

You need very sweet and ripe pears to make a decent perry. A crunchy d’Anjou pear might make for a nice snack, but it doesn’t have a high enough sugar-to-fiber ratio to yield the alcohol content we’re aiming for. Varieties like Bosc or Conference pears, which tend to sweeten significantly as they ripen, make for great perry.

The first stage of vinegar production is to use yeast to convert the sugar in fruit into alcohol. Find a bucket that will leave 15 percent of its volume after the pears are in. A 5-liter bucket ​
is perfect here.

Stem the pears (you can leave the seeds in) and dice them into manageable pieces. Blend them into a rough puree in a food processor. It doesn’t have to be completely smooth; just blend until you no longer see individual chunks of fruit.

Place the pear mash into the fermenting bucket. Add the yeast and mix, folding the fruit over to ensure that the yeast is well distributed. Snap the bucket lid shut, ensuring that it’s airtight, then fill the airlock with water and insert it into the rubber stopper. (If you’ve never home-brewed before and this is hard to visualize, just ask the clerk at your home-brew shop or watch a video online. It’s much easier than it sounds.)

Move the bucket to a spot that’s slightly cooler than room temperature—about 18°C/64°F is ideal. Fermenting in warm temperatures can impart murky, musty tones to the perry. Ferment the perry for 7 to 10 days, depending on how much residual sweetness you want. Let taste be your guide. During fermentation, open the lid every day and stir the contents with gloved hands or a sterile spoon. There won’t be any juice for you to taste in the early stages, but dipping a spoon into the pear mash will tell you everything you need to know. As the mixture ferments, the lid will puff up and the airlock will occasionally gurgle. This is caused by the carbon dioxide produced by the yeast, and it’s perfectly normal. We don’t advise taking the perry all the way to complete alcoholic fermentation (14 to 16 days), as you want some residual sugars to balance the flavor of acetic acid. If you find that your perry has fermented too far, you can simply add some fresh, strained pear juice to dilute it. It will be easier to adjust the balance of sugar at this point than later.

Once the pears have finished fermenting, you’ll need to press the mash for its juice. At Noma, we do this with a cider press—basically a perforated metal or wooden drum that squishes juice from the fruit with a hand crank. You put the fermented mash in a cloth bag and place the bag in the drum. Turn the crank and out comes the juice via a spout at the base.

If you aren’t lucky enough to own a cider press, pushing the mash through a good old-fashioned chinois lined with cheesecloth will do the trick. Some fruit will pass through to the other side, so strain it again through a fine-mesh sieve or cheesecloth, but no need to get obsessive about straining. Viscosity isn’t your enemy. A thicker juice makes wonderful perry with great mouthfeel and body.

So now you’ve got perry. And while this is a chapter about vinegar, you could chill this down and enjoy it right away, or warm it up and add some mulling spices, or transfer it to swing-top bottles and let it ferment further in the fridge into sparkling perry. However, the following step will make the last option impossible, so decide now if you want to turn your perry sour.

We don’t want yeasts interfering with the flavor of the vinegar or continuing to ferment sugar into alcohol, so we kill them off. Transfer the strained perry to a pot with a lid and heat it to approximately 70°C/158°F—steaming but beneath a simmer. Cover the pot and hold it at that temperature for 15 minutes, stirring occasionally, then pull it off the heat and allow to cool to room temperature.

If you were to pour the perry into a couple of mason jars, cover them with cheesecloth, and leave them on the counter, you’d eventually have vinegar. We’ll call that the long method—you’ll be waiting somewhere around 3 to 4 months for the juice to acidify properly through wild fermentation.

To speed things up and give us more control, we do two things. First, we backslop: Weigh the perry, then measure out 20% of that weight in unpasteurized pear vinegar (or a similar unpasteurized vinegar). For example, if you ended up with 1.8 kilograms perry, add 360 grams vinegar.

The second step is to aerate the vinegar. AAB need oxygen to function, and the long method does nothing to facilitate that. Begin by selecting the right fermentation vessel. You want something with lots of surface area, but nothing metal. You can use the same bucket you used for fermenting the pears, or switch to a 3-liter jar with a wide mouth. Pour the backslopped perry into the vessel. Wearing gloves, place the air stone into the liquid, making sure it rests on the bottom of the container. Snake the hose out the top of the vessel to the air pump and cover the vessel with cheesecloth or a breathable kitchen towel. Secure the cloth with a rubber band but be careful not to impede the flow of air through the hose. However, fruit flies absolutely adore the smell of vinegar—they’re also known as “vinegar flies” in some regions—so it’s important to make sure the seal on your cloth is unbroken. If there’s a gap where the tube exits the bucket, use a piece of tape to shut it. Plug in your air pump and leave the perry to ferment at room temperature.

With constant aeration, you’ll be able to turn the vinegar around in 10 to 14 days. Start tasting the vinegar daily after a few days. If the taste of alcohol is still noticeable, the vinegar needs to ferment further. You could use a pH meter or pH strips to test how acidic your vinegar is—a pH range of 3.5 to 4 is usually just right—but in all honesty, we find taste to be a better guide. Sugar, viscosity, and the flavor of your vinegar can all affect the perception of acidity on your tongue. A mechanical measurement may not necessarily lead to the product you want.

Once finished, strain your perry vinegar and store it in capped bottles in the fridge to keep the flavors as fresh as possible, though the vinegar is perfectly shelf stable as long as it’s not exposed to air. If you notice any sediment at the bottom of the bottle, you can either shake the vinegar before using or, if you’d prefer a clear vinegar, gently pour it off into a fresh vessel, leaving the sediment behind (what we call “racking”).

Simple Directions

1. Dice the pears and blend them into a coarse puree.

2. Place the pear mash into a fermentation vessel, add the yeast, and cover with a lid and an airlock.

3. Allow the mixture to ferment for 7 to 10 days.

4. Press the mash to harvest the perry.

5. Transfer the perry to a new vessel, backslop with unpasteurized vinegar, and set up an air stone and pump.

6. Ferment until sufficiently soured, 10 to 14 days. Strain and bottle the finished vinegar, and store in the refrigerator.

Suggested Uses

Perry Vinaigrette

Perry vinegar has a light and delicate sweetness that yields the nicest vinaigrette of any vinegar in our repertoire. Whisk together 3 parts good olive oil, 1 part perry vinegar, and a small dollop of grainy mustard. Season with salt, and you’ve got all you need to elevate fresh salad greens, blanched wax beans, or lightly sautéed kale.

Pear Hollandaise or Béarnaise

Because perry vinegar doesn’t have the same up-front harshness of your average white wine vinegar, it can stand alone as the base for sauces like hollandaise or béarnaise, where many classic recipes call for white wine vinegar diluted with white wine. Measure 250 milliliters perry vinegar into a small pot with a sliced shallot and a dozen peppercorns. Reduce the liquid by about two-thirds, then strain. Transfer the reduction to the top of a double boiler, add 3 egg yolks, then cook and whisk until the sauce thickens and falls off the whisk in ribbons. Season with salt and a bare pinch of cayenne pepper.

To double down on the fruitiness, brunoise firm but sweet pears and let them macerate in 250 milliliters perry vinegar for a couple of hours. Drain the pears, reserving the vinegar. Use the vinegar to make the reduction for the sauce, and fold the pear brunoise into the sauce. It’s a vibrant and full-bodied sauce that you could just as easily serve alongside grilled hanger steak as with a bowl of barely cooked peas.

Excerpted from The Noma Guide to Fermentation by René Redzepi and David Zilber (Artisan Books). Copyright © 2018.