tl;dr ... If you think that the article is too long, here's the short version

Abstract

Primary Fermentation

A loaf of bread of a typical size use approximately ½ hour to raise until doubled in size, if you ferment with 25g (½ package) fresh yeast. Every time you halve the amount of yeast you double the fermentation time.

Proofing - Secondary fermentation

Bread with 25 g (½ package) of fresh yeast needs to proof (second fermentation) for twenty minutes and every time you halve the amount of yeast, it must be proofed for an additional twenty minutes.

Another coarser but easier mnemonic,  is that the proofing takes approximately half as long as the fermentation, if you use plenty of yeast.

Yeast conversion amounts

Test #2 - Wet Dough

Setup from left: 1/16 pkg, 1/8 pkg, 1/4 pkg, 1/2 pkg Yeast - 80% water

Conclusion of the experiment

What happens here is a bit is funny in that the dough seems to wait for approximately ½ hour before it starts. And then taking as long as the dry dough to ferment. A half hour for half a packet of yeast and then a doubling in the fermentation time for every halving in the amount of yeast. So it was the same result as in test #1. Except that there was ½ an hour added in the beginning of the fermentation.

This does not seem right to me! In my experience a wet dough should not be slower than a dry dough. Quite the opposite. So I'm afraid that other factors are at play here. It may be because the yeast is somewhat older in this test. Just a few days shy of the sell-by date. Or because the room temperature was a little lower during this test. So the dough might need to spend half an hour to "wake" up. Or perhaps my tap water was extra cold that day. Note to self. "Make an attempt with the same dough, but with fresh and old yeast."

Test #3 - Medium Wet Dough

Setup from left: 1/16 pkg, 1/8 pkg, 1/4 pkg, 1/2 pkg Yeast - 70% water

Conclusion of the experiment

In this test the same thing happens as in the previous test. The dough "waits" for half an hour, and then it goes off. Then it more or less follows the  "half an hour / ½ a package yeast" rule. This rule however is skewed when using very small amounts of yeast.

Again I did not use a completely fresh yeast, and the temperatures might have been different, so I guess that's why there is an extra half an hour too. But as I said, I need to test this more.

Test #4 - Proofing, Medium Wet Dough

Setup from left: 1/16 pkg, 1/8 pkg, 1/4 pkg, 1/2 pkg Yeast - 70% water

The same recipe as test #3 but I measure the secondary fermentation time instead of the primary.

When the dough has fermented the first time, you divide it as needed, and then shape it loosely. This process is also referred to as de-gassing (Punching down) (Which is a very poor description of the actual process).

Here I use a medium wet dough with the same four different amounts of yeast as in test #3. I then let them ferment 4, 2, 1 and ½ hour before I start filming. Following my own results for primary fermentation. So they are ready to proof at the same time. This is the easiest way is to compare the proofing time. And the only way to film it at the same time.

After the first raise, I put the dough onto a table dusted with flour, and shaped it into a ball, before putting it down into the "measuring containers". I was careful to punch out as little gas of the dough as possible. The dough starts out with a larger volume in the beginning than at the first 3 attempts. This is intentional. I still measure the "doubling size" in relation to the unfermented dough. This is still just under the white tape on the left container.

Conclusion of the experiment

I was actually not sure what would happen here. Since all the doughs had fermented to twice their size one time already, I imagined the following scenarios was possible:

• They had all catched up to the same stage in the process and would be the "same level". So by now there would be equal amounts of yeast in the dough, and they would all raise at the same speed from here on.
• That they would keep their relative amounts of yeast, in the amounts that they were added in the beginning, so the proofing would also take twice the time for each halving of the amount of yeast. Just like in the primary fermentation.

In fact, it ended up somewhere in between. First there was a ten-minute pause, where nothing happened, and then it took approximately 12 minutes extra per halving of yeast. This I had not expected.

But this is hard to remember and unnecessarily accurate. So the rule of thumb for proofing is:

"20 minutes for one half a pack of yeast, and then 20 minutes extra for each halving of yeast."

This will result in a proofing time that is a bit longer than is really necessary for small amounts of yeast, but it is not that important. Fifteen minutes per halving of will be too little for half a packet of yeast. An amount that most people probably use regularly. But with smaller amounts of yeast "1 extra quarter per halving" is also a fine rule to remember. If you then also remember to use 20 minutes for ½ a packet of yeast ...

Another reasonable rule of thumb would be: "The proofing takes half as long as the primary fermentation." Although this model breaks when you get down into the small amounts of yeast. There the proofing is somewhat faster than half the primary fermentation. 

Test #5 - Fermentation under different conditions, medium wet dough

Setup from left: fresh yeast (control trials) / old yeast / plenty salt (2.5% = 12 g) / milk instead of water

Here I make a test where I use 1/8 pkg  of yeast for all batches of a medium wet dough (70% hydration) (like in test # 3). And then I do as follows:

• Fresh yeast is the control experiment. Which corresponds to the 1/8 package of yeast in the dough, in an test #3.
• Old yeast is yeast that is right at its "best before" date. It appears dry and brownish, but otherwise there should be nothing wrong with it.
• Many recipes uses milk instead of water, so it's nice to know what happens to the fermentation time with milk.
• Plenty Salt: you typically use between 1.5% and 2.5% salt in a bread. The 2.5% is among the highest that is realistic to use. And since salt inhibits the fermentation is also handy to know by how much.

Conclusion of the experiment

This result is a bit funny compared to the other results I've had, I would have expected a fermentation time at 2 - 2½ hours for the control experiment, and 2 hours, from my rule of thumb in relation to the amount of yeast. But it actually went a little faster.

I think that was because this video was recorded on a warm spring day with the sun shining through the window. So the room I recorded in has had to be 24°C-26°C (75°F-79°F) degrees. You can also see that the video "flickers" a little due to the sun that shines into the room once in a while. but it does show very well that it is a biological process with living organisms that is depends on many things. Especially with the smaller amounts of yeast, a temperature difference shows its influence.

The previous tests/videos were made on cool spring days, so my kitchen was cooler too. The fermenting batches was placed close to the outer walls, that would also have been cooler on the cold days.

Another funny thing is that the dough with the old yeast actually raises faster than dough with it the fresh yeast. This is a surprise. I suspect either it may be because I used a different bag of flour. Although it's the same brand of flour perhaps there may be the difference. Or I could have cut the yeast a little crooked so it was not exactly 1/8 of a package. However, that is not as likely as I was pretty careful. The difference is approximately a hour compared to 7 quarters hours for the total fermentation time, which is a 14% difference. So it does not mean sooo much in practice over a 2-hour fermentation. But if it IS because I've switched to another bag of flour, is nevertheless an interesting result which I had not considered.

The dough with the maximum amount of salt took half an hour longer to ferment. Or 1/3 extra fermenting time. I believe that is very realistic as a general result.

According to my experience a dough without any salt at all raises like crazy. But since the only place where an unsalted bread is typical is in Tuscany (due to tax-political problems in the renaissance), I therefore think that "no salt" it is an unimportant thing to measure in the rest of the world :-S So I only measured the typical ranges of salt in bread. "a little" and "a lot" ...

The dough with milk is yet another slow surprise which may be due to several things. The milk came straight from the refrigerator and is 5°C (41°F). I did it this way because I believe this was the most realistic situation when you ferment something with that little yeast as in this test. You don't heat up the milk first. However, the cold milk may have been a reason for the extra fermentation time. The tap water I used for the other tests was approx. 16-18 ° C for comparison.

Milk contains a lot of "solids" even though it seems like a liquid. They are the ones that can turn into cheese, sour milk, Greek yogurt, etc. When I made my bread recipes I tried to mixing some batches by touch to compare how wet the dough felt during kneading. I found out that I actually needed to make a dough with 4 dl (1.7 cup) milk for a dough comparable to one with 3 dl (1.3 cup) water, and the I had to use 1 dl (0.4 cup) less of flour, to offset the solids in the milk.

So a dough based on milk, with the same liquid percentage as a water based dough, is much drier. Whether it played a role I do not know. There is nothing in the tests where a dry dough seem to go any slower.

Milk contains fat which inhibits fermentation. I used semi-skimmed milk with 1.5% fat so it should not have much impact. On the other hand, there are sugars and proteins in the milk which should facilitate the ferment. So I am somewhat perplexed. I have no idea why milk is slower. It's against my intuition. But it takes about 1/3 as long to ferment so it's pretty unique. If I should ever want to do more fermentation tests in the future it would be a fine candidate for further tests.

Test #6 - Forced fermentation with only a little yeast (tuning), medium wet dough

Setup from the left: water (control ferment) / 1 tbsp sugar / 1 tbsp vinegar / hot water (60 ° C)

Again, a test based on test # 3, with 1/8 package yeast in each container and 70% hydration. I probably should have used 1/16 of a package, as it is the smallest amounts of yeast that it is the most interesting to speed up. But I needed that it did not take too long to complete, as I was running out of day. So I did it like this:

This was recorded on the same day as the hot day but in the evening. So it was a bit cooler. It is also visible in the fact that the control ferment was only 10 minutes faster than in the other days where it was a lot cooler in the room.

I like to ferment my dough with as little yeast as possible. But sometimes I do not have the luxury of time to wait the 4-12 hours that I normally use. Then it's practical to speed up the process a bit. Sugar, vinegar and hot water are the three methods I know of. However, I wanted to use so little sugar and vinegar in the test that you cannot taste them in the final bread. Therefore I only use 1 tablespoon of each.

When I make the "no knead bread / world's best bread" with the short fermentation time, I have used all three methods in this test at the same time, since I had read that it would be effective. But I've always been curious as to what it is that works and how effective each element is. So in this test I have separated the different methods.

In the dough with added vinegar, there was a distinct difference in the dough during kneading. It was much more loose and "runny" after a short kneading. As if there was more water in it.

In the dough with the hot water I took away ½ dl (0.2 cup) water, in which I dissolved the yeast. I then slowly kneaded the hot water into the flour and salt. Finally I added the water with yeast. This was to avoid killing the yeast with the 60°C ( 140°F) water. The finished dough was approximately 40°C (104°F) after 5 minutes of kneading. The dough seemed to be more dry than the other batches. As if heating the water made the flour absorb the water better. Which is not unthinkable as heat is known to speed up chemical processes.

Conclusion of the experiment

Sugar in the dough had no effect. In fact, it went slower. This surprised me. I had expected that the yeast would had loved it. But no. At first I dissolved the yeast in the water. Then I added the sugar and the salt. Finally I added the flour and did the kneading. Salt and sugar in high amounts are a poison to yeast, so it is possible that the salt and sugar in the water, along with the yeast, gave the yeast a slight shock. Resulting in the longer fermentation. It's the only explanation I can come by. But I did mix the dough quickly to avoid that, and it isn't usually a problem.

In any case, sugar is generally a bad idea in a dough, as it makes the crust darken faster. This makes it difficult to get a thick crispy crust without burning the bread. It is better to use a long fermentation time to develop the starches and sugar in the flour. Which does not seem to darken as much.

Vinegar in the dough had less effect than I thought it would. But nevertheless, it's approx. 1/3 faster, so it certainly has an effect. Bakers have also put citric acid in their bread mixes for years. Precisely for that reason.

When I say 1/3 it is because it took less than 10 minutes from the test experiment was kneaded until the dough with vinegar was kneaded. So the correct time should actually be 1:32 from the vinegar test. If you have to be absolutely correct. It has not had any great significance in any of the previous attempts, but here it is relevant.

You can also use lemon juice instead of vinegar. However, I am not quite sure whether a tablespoon is enough. I don't know the difference  of the acid content.

I used plain white vinegar in the trial, but I usually use apple cider vinegar when I actually intend to eat the dough. It is not necessary, but it adds a little extra scent to the bread.

The hot water is clearly the winner. The dough raises twice as fast. So this is a no-brainer.

The final tuning rule then is that you should use warm water and 1 tbsp of vinegar if you want to make your bread raise quickly with only a little yeast. Overall it can ferment three times faster when combined. I have not tested this with a timelapse video, but it fits with my experiences when I do it. " No Knead Bread / World's best bread " takes a 4 hours to ferment this way.

Bonus - Test #0 - Test trials ...

Setup from the left: 6 g, 12 g, and 25 g of yeast - 80% hydration.

At first I made a test trial of dough from the "No knead bread / World's best bread" to get a sense of how I should go about the experiment.

• 4 dl water
• 8 dl flour
• 2 tsp salt
• 25 g, 12 g and 6 g of yeast

I kneaded the doughs for 5 minutes with the Kitchen Aid meat hook, and set the camera to take a picture every 5 seconds. (It resulted in almost 4000 images.)

I thought I was clever putting the clock in the background so you can see how much time has passed. But it just seemed confusing in the end, so I dropped that in the final tests.

I would also crank up the speed of the video by four times. So in the final tests I only used pictures from every 20 second instead of every 5

I also noticed that the dough ended up very was close to the edge of my test containers, so I decided to use a slightly smaller amount of dough in the final tests. Dough is such a bother to remove from furniture ...

I was actually not aware that a dough would raise to 4-5 times the starting size before collapsing.

So all in all it was an instructive experiment for me ...

I baked most of the doughs, and even the ones that had collapsed and waited until the next morning actuallay made for quite nice breads. So it is pretty hard to overferment a dough.