Gérard Rubaud's Apprentice Loaf

The Apprentice Loaf is Gérard Rubaud's teaching bread. He has developed the formula in collaboration with two of his former apprentices, Trenton and Justin, largely in response to customers' request for more whole grains. It is still a work in progress (what isn't with Gérard anyway?): his parting recommendation to me when I left was to adjust the hydration down.
The picture above is of one of the loaves I made at home based on the formula. Gérard wouldn't have given it his quality control stamp as he doesn't do grignes (the ears in the crust): his customers eat his bread mostly for breakfast and in sandwiches and grignes get in the way. Plus he himself doesn't like the hard bite or the concentrated taste. So he always scores his bread shallowly and at a sharp angle. I am the opposite: I adore anything crusty: grignes, quignons (bread endings), etc. Since my only "customers" are family and friends, there is enough of both textures in any given loaf to satisfy everybody!
To my mortification, I forgot to take a picture of the loaves Justin kindly gave me for my grandchildren  (they were not to be sold and he had enough for himself and his friends). When I reached my daughter's house, the kids -who are huge bread fans- were so happy to see my load of loaves (and hopefully me as well) that I forgot all about photography! When I remembered the day after, there was still a half-loaf left and I took this shot of the crumb.

Neither Justin nor Gérard were satisfied with this batch: the loaves were overhydrated and as you can see, they didn't get enough of an oven rise. I used a tad less water and my crumb came out a bit tight (see shot below). 

I'll keep working on it until I get it right. Meanwhile my little grandkids pronounced my loaves to be even better than the apprentice's (Sorry, Justin! They are seven- and five year-old and a fiercely loyal bunch. I am sure that if they had met you, they would have said both our breads were equally good.). As it is, the seven-year old granddaughter said: "Wow! This is so good. The best bread ever. As good as an artichoke!". Since artichokes are her favorite food in the world, I consider it a huge compliment.
And truly the bread is good. Spelt tastes endearingly sweet almost as if a dollop of fragrant honey had been added to the dough during the mixing, a practice which Gérard (who despises adding to bread dough anything but the -very- occasional walnut, olive or flax seed) definitely wouldn't condone.
Gérard's Apprentice Loaf Formula

• 76% unbleached all-purpose flour
• 24% freshly milled whole spelt
• 82% water (to be adjusted as needed)
• 2 to 2.6% salt (according to taste)
• 17% levain at 58% hydration (percentage to be increased in the winter as needed)

My adaptation of the formula

Ingredients: (for four loaves scaled raw at 627 g) 

• 1028 g unbleached all-purpose flour
• 252 g whole spelt (I used freshly milled as does Gérard)
• 972 g water (Gérard uses all of the water for the autolyse but I like to reserve about 50 g in order to adjust the hydration later as needed. So I used about 900 g+ for the autolyse and added the rest as I mixed. This may vary each time I make the bread as it depends on the flours, the weather, the temperature, etc.)
• 31 g salt
• 253 g mature levain at 58% hydration

Method: (this dough was mixed by hand)

1. Mix both flours with the water until the flour is completely hydrated and let rest, covered, for about 40 minutes
2. Add levain to the autolysed dough and hand mix until incorporated (Gérard recommends pulling long filaments off the levain instead of cutting off chunks as they incorporate much more easily. Not only did I follow his recommendation but I placed these long pieces of levain on top of the dough during the autolyse, so that everything would be exactly at the same temperature. It worked beautifully but I got a surprise: the dough actually swelled up as it usually never does in the absence of a leavening agent and I can only think that some of the wild yeasts from the levain transferred to it even without mixing. Which means that it wasn't a real autolyse...)
3. Add the salt
4. Mix until incorporated and adjust the hydration as needed
5. Cover and leave to ferment for 4 to 6 hours or more (depending on room temperature), giving the dough a few folds as needed
6. Scale at 627 g and pre-shape as a boule
7. Let rest, covered, for 20 to 30 minutes (again depending on room temperature)
8. Shape as a batard
9. Let proof about one hour or until the dough stops bouncing back under the gentle pressure of two fingers
10. Bake with steam in pre-heated oven (470°F/243°C for 10 minutes then lower the oven temperature to 450°F/232°C and continue baking for another 20 to 25 minutes, turning the loaves half-way through to ensure even baking (again these temperatures are given solely as an indication. I am spending the summer in a little cabin where the oven is small, very old and rather weak and I have to crank it up to the max to get a rise out of my bread. I actually set it on 500°F+  for the initial 10 minutes and on 470°F for the remaining 20 minutes or so but, from past experience with my regular home oven, I would say 470° F and 450°F should do the trick. If your oven is very efficient however, these temperatures might need to be adjusted down).
11. Cool on a rack.
12. Enjoy!

Gérard Rubaud's Apprentice Loaf is going to Susan from Wild Yeast for her weekly edition of Yeastspotting.


Related posts:

• Gérard Rubaud: the Never-Ending Quest
• Meet the Apprentice: Justin Rosengarten
• Gérard Rubaud

Meet the Apprentice: Justin Rosengarten

Justin Rosengarten, 24, who holds a Bachelor of Fine Arts in visual arts from the Rhode Island School of Design, came to bread the same way as many other bakers I have had the pleasure of meeting since I started this blog: out of sheer passion.
He isn't absolutely convinced yet that bread is his ultimate calling (he has given some thought to being a furniture designer, a children's book designer or a pianist) and as he puts it, "I'll continue to dance until I find" but he has a pretty good idea that it might be it.
Even before meeting Gérard and deciding to apply to the apprenticeship program, he started on his own to learn what he could about bread: "Frankly I thought there was nothing to it".
He built an oven at one of his friends' house in Vermont: "I wanted to have this oven on my résumé."  But he needed more exposure to bakery work.
His Vermont friend called Erik Andrus, the local baker, and asked him whether he might be open to have Justin come and watch him make bread. Erik, who owns Good Companion Bakery near Vergennes in Northern Vermont, invited Justin to come over and actually hired him to sell bread at the farmer's market.
On his free time, Justin decided to go visit other bakeries in Northern Vermont. He googled Vermont bakers, found Gérard Rubaud through this blog and the rest is history. When I met Justin, he was on the fourth day of his apprenticeship with Gérard. 
Having since left the program for personal reasons, he no longer works at Gérard's. I wish him the best of luck. I am hoping he'll appear again on this blog, this time in the Meet the Baker series...

Gérard Rubaud's Apprenticeship Program - Updated

(see updates at end of post)

Gérard demonstrating folding to Justin Rosengarten

First thing first, let's get the disclaimer out of the way: I have zero financial (or other material) interest in Gérard's apprenticeship program. I don't make a cent if anyone signs up for it (or for any other training program offered at the bakery) and since I live on the other side of the country, I don't even get to taste the apprentices' bread, except on occasional visits back to Vermont. My one and only reward is knowing that by spreading the word about the program, I am helping perpetuate a skills that is very dear to my heart.
Don't get me wrong, if I lived in Gérard's neighborhood, I would have no qualms about accepting an apprentice loaf now and then, just for quality assurance purposes, mind you! ;-). Better yet, I would probably apprentice myself and churn out apprentice loaves for family, friends and neighbors for days on end. But since I don't, I am just happy to describe the ins and outs of the program and let you decide for yourself whether or not it fits your calendar and your needs. It requires a big investment of time and energy and it is not for the faint of heart. But once you have gone through it, you do know how to bake one of the most naturally aromatic pure levain breads in the world.

In a nutshell

• Gérard considers an artisan baker to be someone who bakes bread for his neighbors. He sees it as an heresy to truck bread away to a distant city. In eighteenth-century Paris, a baker couldn’t sell his bread on the Paris markets unless he had baked it intra muros (inside the city itself)
• If anything goes, then the artisan is no longer respected and industrial bread sneaks back in. A self-respecting baker doesn’t use the artisan label to sell industrial bread
• The idea behind the Apprentice Loaf is to give credibility to artisan bread by training credible bakers
• Under the program, the apprentice acquires both technical and business skills: he or she learns the technical side of bread-baking and is encouraged to open and maintain a dialogue with the stores that distribute the bread.

Background

• Gérard enjoys having people working with him
• He also knows he can no longer work as he did ten years ago and he’s aware that with age encroaching, things are not going to change for the better. The apprenticeship program is a way for him to prepare for a transition
• On doctor's orders, he only bakes five days a week but to his way of thinking, the baker's social responsibility is to make fresh bread available to his customers seven days a week. With two or three apprentices each selling his or her bread to three stores, he could distribute fresh bread six or seven days a week to 75% of the stores which sell his bread now
• Many of Gérard's customers have asked for a bread with a higher percentage of whole grains and the Apprentice Loaf (which contains close to 30% whole spelt) would satisfy that request.

Philosophy

• Bakeries already existed in eighteenth-century France while there were none in America at the time
• Bread culture goes way further back in Europe. Professional bread-baking came late to the United States and there is no existing bread-baking network
• There are no state- or privately funded programs promoting bread-baking in the United States
• Even today, less than four hundred schools have a bread-baking program and too often, in Gérard's opinion and experience, this program doesn’t teach proper artisan skills
• Gérard considers that apprentice bakers need to have access to a complete practical training which baking schools cannot provide
• Moreover these schools are very expensive and can take up to two years. In Europe, bread-baking schools are partially subsidized by the state
• It is Gérard's firm belief that in coming years, bread production and sales will be completely separate. Sales will take place in high-traffic areas where production wouldn’t make sense economically
• That’s why the apprentice must learn, not only to make good bread but to sell his or her bread wholesale to the stores which will carry it (developing a relationship with the customer is a good way to stimulate demand)
• At the end of the program, the apprentice knows enough to set up his or her own little production unit and has experience with the market
• The ideal apprentice is confident enough in his or her skills towards the end of the program to start training the next candidate. Gérard's goal is to thus create a self-perpetuating chain of trainers.

Program Description

• In an intensive hands-on program, the apprentice learns the fundamentals of natural fermentation including how to create a pure levain from scratch and maintain it over time
• The program typically lasts anywhere from three to six months (in certain cases, it might even go up to a year), ideally with two apprentices at the same time
• There are no fees involved. The apprentice - who makes the bread from start to finish with ingredients and equipment paid for by Gérard- sells the bread and keeps 60% of the proceeds, the other 40% going to cover the costs incurred by Gérard
• The apprentice is housed on the premises and has a full kitchen and bathroom at his/her disposal
• Depending on his or her other commitments (if any), the apprentice can work up to three days a week, sometimes five
• The apprentice starts his or her day at 5 AM (by then Gérard is done with his own mixing) but usually comes in the evening before to prepare the levain
• The apprentice learns the craft by hand and moves on to the mixer when Gérard thinks he or she is ready to sell
• The apprentice delivers the bread he or she makes but the last word on quality control belongs to Gérard who personally checks all outgoing bread
• The apprentice's bread is the Apprentice Loaf: the formula was developed by Gérard in collaboration with two apprentices, Trenton and Justin. It is already a best-seller with the customers.

The Ideal Apprentice

• Must be passionate about bread
• Doesn’t have to be a young person (age really doesn’t matter)

Hopes and Hurdles

• Gérard doesn’t advertise (although the Apprentice Loaf is sold in a bag describing the program)
• Recruiting is therefore based on word-of-mouth or chance encounters with potential apprentices
• Gérard's style of teaching is old-school French, which means there is no pampering, no cuddling and no gushing, quite the opposite in fact: he is often gruffy and the apprentice needs to be strong and self-confident enough to handle it. When I mentioned to Gérard that the American way was to be a tad more encouraging, he scoffed: he learned his trade the way he teaches it. It worked for him close to sixty years ago and he believes it works just the same today. Think bread boot camp!
• He knows however that he isn’t an easy person to work with (he doesn’t like repeating the same thing over and over and he can be intimidating) and he says he is working on improving his teaching skills
• When the program is fully operational, it will be the "graduating" apprentice's responsibility to teach the incoming apprentice(s): to date, ten apprentices have "graduated" from the program but chosen to skip the teaching part, a fact that Gérard deplores.

Application Process

• For a token fee designed to filter out gawkers and tourists, potential candidates can come and watch Gérard work a full-production cycle from 4 PM to about noon the following day
• Gérard describes the program to the candidate and explains what the apprentice will get out of if
• Arrangements can then be made on the spot
• For more information, send a written request to: Gérard’s Breads of Tradition, 29 Rubaud Rd, Westford, VT 05494 . Please include a phone number where you can be reached.

UPDATE - August 21, 2012: Due to the level of interest generated by the program, Gérard Rubaud now requests that potential candidates send him (at the above address) a one-page resumé describing their past experience as well as their expectations for the future, together with their contact information. He will personally answer all such letters. 
UPDATE - December 5, 2012: Gérard Rubaud is currently only accepting applications for apprenticeships starting after March 2013. Also, because of the huge demand, he now requires baking experience.

Apprentice Justin Rosengarten with a batch of practice loaves just out of the oven

Related posts:

• Gérard Rubaud's Apprentice Loaf
• Gérard Rubaud: the Never-Ending Quest
• Meet the Apprentice: Justin Rosengarten
• Gérard Rubaud

Gérard Rubaud and the Three-Speed Levain

Gérard's regular levain, fermented on second speed, initially (left) and six hours later (right)

What baker hasn't wished his or her levain would ferment a little faster so that mixing can start? Gérard who runs a one-man show on a very tight schedule has devised a method that gives him more control on how fast or how slowly his levain will develop.
He doesn't advocate using this method all the time as he isn't sure of what actually happens within the levain when it ferments faster: does it develop undesirable acids or aromas? He hasn't been able to tell just from tasting the resulting bread. Still he finds it a handy tool to have as it makes for more flexibility.
As for me, when we did the experience described below, since we didn't bake with any of these three pieces of levain, I can't vouch for the taste but I can tell you one thing: the levain fermented on third speed had aromas which were heady enough to make a grown woman swoon. Plus it ended up so round and fluffy I wished I could have used it that night as a pillow. Forget about cloud nine! I'll take cloud three anytime...

Three-speed levain demo

Pictures taken before the start of the experiment
#3 may look a bit bigger than #2 to start with but it is an optical effect. 
All three levains weigh exactly the same.

• Shortly before 8:00 AM, Gérard feeds his regular levain and scales off three 1,650 g pieces which he calls #1, #2 and #3 respectively. Please note that he keeps his levain at 57% hydration and always salts it
• He rounds the three pieces gently
• At 8:20 AM, he places #1 in a plastic box, loosely covered, and puts the box on its side (to make later comparisons easier) (this is first speed)
• He places #2 next to #1 and loosely covers it with a sheet of clear plastic (this is second speed)
• He places #3 next to #2 on a clear sheet of plastic which he loosely wraps around it (this is third speed). 
• When wrapping the levain for third speed, it is important to leave it room to expand as its volume will triple
• The three levains are then left to ferment side-by-side at room temperature (about 78°F) for about six hours

• At 2:20 PM, Gérard uncovers the three levains simultaneously
• Significant differences in sizes can be observed between them, ranging from #1 (the smallest) to #3 (the largest)

• #3 has obviously reached a more advanced stage of fermentation (Gérard's theory is that wild yeast cell counts shoot up when the levain is completely sheltered from ambient air)
• #3's fluffiness makes it much easier to incorporate into an autolysed dough: there is no risk that some pieces of it might remain firm and unincorporated
• For the sake of the side-by-side photo comparisons, Gérard has made all three levains into boules today but when he actually uses the third speed in a production setting, he shapes the levain into a long sausage before wrapping it. The fermentation is even faster that way.

Gérard says he uses second speed routinely and third speed only when he really needs to rescue his production schedule. 

Other Gérard Rubaud stories may be found on this page.

Gérard Rubaud: The Never-Ending Quest

Time has come for a return visit to the bakery on the hill and to the maestro whose life's work is to charm wild yeasts out of plain bags of flour and grains and choreograph them into intricate ballets of flavors and aromas.

Save for the colors of the season, the landscape hasn't changed: the pond still stares at the sky, the girl still dances on her bluff and the trees are as watchful as ever.

The dogs romp in the meadow, there is enough wood near the house to feed the oven for months on end... No, not much has changed indeed since my last visit to this corner of northern Vermont.

But the baker himself, ah, the baker remains a moving target. What he is seeking in his endless quest no one can really tell, maybe not even himself. In the three years I have known Gérard (only three years and yet I feel as if I had known him all my life), he has changed almost everything in his formula, changed his levain, changed his methods, changed his timeline. The bread is indeed better than it ever was but that's incidental. He will never get where he's going but that's fine. If he did, all light would fade away from life.
In this seemingly changeless environment, what keeps the baker going is change. Not change for change's sake, mind you! Change because nothing actually ever stays the same: temperature and humidity go up and down, protein and enzymes differ from one bag of flour to the next, customers call and ask for big holes in the crumb, others request a denser crumb ("I don't want to wear a bib when I eat my toast and marmalade"), others yet follow variations in the taste of the levain as sports fans follow a favorite team ("What did you do to your bread? I love it, keep it that way!" or "I liked last week's better"), they ask for more whole grains, for less whole grains. They are a vocal bunch and bread to them is definitely not the squishy stuff that comes in a plastic bag on the supermarket shelf. Their bread carries Gérard's signature and they like it that way. They queue up at the stores. Peter, the man in charge of the deliveries, says people wait in the parking lot for his van. They follow him into the store and wait while a price label is affixed to the bag, then they make their move.

The breads on the left haven't been bagged yet as they are still too warm. They will be before they get to the store.

Gérard could sell much more bread that he currently does, except that he can't because it would be physically impossible for him to bake much more than 150 loaves a day five days a week. He learned that lesson from the stroke that left him temporarily paralyzed and permanently disabled six years ago (he used to bake seven days a week). But as he sees it, the most important part of a baker's job is making good bread every day for local customers (his "friends and neighbors" as he calls them). Never mind expanding...
Fame knocks at his door now and then but he sends it on its way. Gérard's bread was recently featured in Saveur magazine's round-up of the best breads in America and when I saw a picture of one of his loaves in the print version of the article (the online version is a crumb shot and I have no clue whether or not it is indeed his), I gasped and picked up the phone: "Gérard, what happened? The bread looks awful!" He chuckled: "Yes, they requested that bread be sent to them for a photoshoot but it arrived too late. The shots were done. So they asked my permission to use just any bread picture and I said, fine. I don't care, I am not selling bread across America. My neighbors are whom I bake for and they know my bread"...

The crumb on Gérard's bread on the day I arrived (a very hot and humid day)

What you'll find below is a snapshot of Gérard's current process and the thinking behind it. Consider it as a moment frozen in time. It will have changed again by the time I go back.

Flours

• Gérard currently uses 12% freshly milled whole-grain flours in his everyday bread (as opposed to close to about 30% when I first met him). He says his customers have asked for a less rustic crumb
• This whole grain consists entirely of spelt right now but he will switch to half-spelt and half- hard red winter wheat when the harvest is in and he can get Warthog wheat again from Vermont farmer Jack Lazor as the flavor of that wheat is simply extraordinary*

Levain

• Gérard originally creates his levain from 50% wheat and 50% rye. After the very first feeding, he only uses all-purpose flour (AP)
• He switched to an all-white levain because he wanted more elasticity. He had had some issues with his previous levain tearing and decided to give priority to texture over taste (not that the taste is any less complex and marvelous, just different)
• He keeps it at 57% hydration
• The smallest amount Gérard ever mixes (his old Hobart doesn’t take less) is: 700 g AP flour, 400 g water, 300 g levain and 6 g salt. That is the first build, always
• Feeding a levain again as soon as it doubles helps create anywhere from 15 to 30% more wild yeast cells. In Gérard’s experience, the first time, the levain doubles in four hours, the second time 20 to 30 minutes faster and the third time, 40 minutes to one hour faster than the first time. That’s when the levain is at its peak
• With such a levain, it is possible to make croissant dough with very little butter using whole grains
• Currently the levain's schedule is as follows: first feed at 8:30 PM, second feed at 5:00 AM, third feed at 3:40 PM (for a 9:30 PM autolyse and a 10:15 PM mixing)
• A baker who normally feeds his or her levain a percentage of whole grains must put it on an all-white diet before storing it in the fridge or it might ferment too much and develop unwanted acids

Autolyse

• Uses all of the water in formula
• Duration: 30 minutes at least and up to 6 hours if desired/necessary
• Takes place at room temperature which, in Gérard's case, is usually in the high 70's
• It takes a while to calculate dough hydration taking the texture of the levain into account. A levain that is too flexible will result in a dough that will need one or two folds to be strong enough
• A six-hour autolyse only reduces later fermentation time by about 40 minutes but makes the dough silkier. An added benefit is that the dough can be mixed right away when the baker arrives at the bakery. Of course in a professional setting, it usually only works for the first batch as the mixer is needed for other doughs
• Flour and water should be mixed for less than 3 minutes (first speed). Don’t mix until the dough becomes homogenous: you want unaggregated lumps that will not hamper gluten formation. The resulting crumb will be softer
• Gluten will develop by itself over time. The baker’s role is to make sure that a maximum of water hydrates the amount of flour in the formula. Once the flour is hydrated, the mixing must stop immediately

Levain Incorporation

• If the levain is flexible enough, it should incorporate in no time

Adding salt

• Once the levain is fully incorporated and dough turns shiny (it takes less than 3 minutes), add the salt

Total Mixing Time: 9 minutes maximum

• Mixing is always done in first speed (Gérard has disabled the second speed on his mixer to make sure it wouldn't be used)
• 3 minutes maximum for the autolyse
• 3 minutes maximum to incorporate the levain
• 3 minutes maximum to incorporate the salt
• Ideally these times should be further reduced if possible

Bulk Fermentation

• Once the levain and the salt are incorporated, the dough is transferred to the wooden fermentation box where it remains for a minimum of 4.5 hours (room temp: about 78°F)

Folding

• Generally speaking Gérard only does one fold and it happens post-bulk fermentation after transferring the dough to his worktable (and if possible without overlapping the folds)
• The exception is when the baker has over hydrated the dough thinking the flour was very high in protein when in fact the protein level was inferior or the quality of the protein poor. The resulting dough is runny and folding is a way of strengthening it

Dividing and Pre-Shaping

• Gérard starts dividing the first batch at 3:30 AM
• He scales at 800 g
• He pre-shapes the divided dough and lets fermentation start again by allowing the dough to rest for at least 30 minutes and up to one hour (if room temperature is cool)
• Gérard likes to keep the dough in its pre-shaped form for at least 45 minutes: he finds it easier to work with afterwards and gets better results
• If room temperature is around 78 to 80°F, the ideal is to allow the pre-shaped dough to rest for one hour
• This lengthy rest enables the baker to give the dough any shape he or she wants afterwards. It works better if the dough hasn’t been pre-shaped as a boule however: in boule form, fermentation would go too fast
• A lengthy pre-shaped rest enables the baker to decrease proofing time

  Shaping

• After a 40-minute rest, Gérard gives the dough its final shape
• The shaped dough is transferred to flour-dusted couches

Proofing

• Proofing is the third stage in the fermentation process (levain + bulk + proofing)
• A good way of knowing when proofing is done is to apply two fingers on the dough (with very little pressure). If the imprint of the fingers doesn’t bounce back and remains on the dough, proofing is done. If the imprint disappears right away, proofing isn’t over
• Total fermentation time depends on the liveliness of the levain and the amount used in the formula: the less levain in the dough, the longer the total fermentation time. For a dough containing 25 to 30% levain, proofing lasts about two hours (the longer the dough rests in its pre-shaped form, the shorter the proofing)
• Gérard no longer retard the proofing loaves (as he started doing last time I was there). He says he prefers to stay away from newfangled methods of making bread as the traditional way has always worked for him. Switching trays of bread from a warm room to a cold room and back to warm is also too physically demanding to make it worthwhile: Gérard currently has no help in the middle of the night. Peter only comes in in the morning to carry the trays of bread to the oven and back and to take care of bagging and delivering

Baking

• The first batch of bread goes into the oven at 8:00-8:30 AM
• Oven temperature is between 485 and 525°F
• Gérard "power washes" the sole of the oven with water before he starts loading (in the winter when air is very dry he also adds steam). But his oven has no venting system and the thirty-six breads he bakes together lose 10 to 12% of their weight when baking, thus providing enough humidity
• Gérard scores his bread holding his lame at a 30° angle. His cuts are very shallow and he never lifts the skin of the dough. What he's shooting for is a very thin crust with hardly a grigne (grigne is French for an ear in the crust)
• For an 800 g bread (raw dough), baking time is 35 minutes.

* Jack Lazor just harvested his Warthog wheat. He says that he brought in eighteen tons and that there will be plenty for Gérard.

(photo courtesy Jack Lazor)

Related posts:

• Gérard Rubaud and the Three-Speed Levain
• Gérard Rubaud's Apprenticeship Program
• Meet the Apprentice: Justin Rosengarten
• Other Gérard Rubaud's posts
• Gérard Rubaud's Apprentice Loaf