Same temp. same yeast same ingredients, why does sometimes my bread not rise?

Test your yeast 1st.

In a small bowl or cup, put about 1/4 cup hot water 100 - 120 degrees.

Put a pinch of yeast and a pinch of sugar or flour and place in a warm place like a closed microwave free from drafts.

Check your concoction in about 10 minutes.

If it's foamy and bubbly, your yeast is good.

If it looks like tan water - its dead. Don't use the rest of the packet or jar- whatever you have.

Sunspots.

Honestly, sometimes there simply is no plausible explanation for why yeast does or doesn't work the way it usually does. Humidity is a factor. Temperature is a factor. The age of the yeast is a factor. Lots of things you never even thought of can be a factor. Once I got a really bad result with yeast dough because the lovely tile countertop where I rolled my dough was too chilly. After that, I learned to heat up the countertop on cool days by placing a cookie sheet (with sides) on it and pouring hot water into the pan.

When you're planning yeast dough, it is always a good idea to have a backup plan just in case the sunspots are active and your yeast isn't.

Instead of fresh yeast, most of us use dry yeast, either instant active dry yeast or active dry yeast. The difference in the two is how the yeast cells hydrate or absorb water. Instant active dry yeast does not have to be hydrated in water for five to ten minutes prior to mixing as active dry yeast does. Active yeast is mixed in water, the particles are dissolved, and the yeast is allowed to grow until the mixture becomes foamy. Then it is added to the flour. The cells of instant dry yeast are porous to absorb water and can be put directly in the flour without waiting for the yeast to hydrate. However, so that the yeast does not have to compete with the sugar or other ingredients for moisture, it is best to mix the yeast in only a portion of the flour. A method that works well is to mix the yeast with about one-third of the flour to create a very wet batter where the yeast cells will hydrate easily and then, add the remaining flour.

And yes, yeast is alive. It is neither plant nor animal but a fungus. We add it to the flour in its dormant state and expect it to thrive in our dough with moisture and the proper temperature. Under the right conditions, the yeast cells feed on sugar and multiply. A loaf of bread, ready to go into the oven, may contain millions of yeast cells. (The little particles found in a yeast packet are not yeast cells. They are an agglomeration of yeast cells mixed with dextrose or starch into larger balls containing many yeast cells.) As the yeast cells feed, they expel carbon dioxide and alcohol. The carbon dioxide gas rises through the bread dough and is captured by the gluten structure in the dough to form air cells. The alcohol and other excretions impart a “yeasty” flavor to the dough. Master bread bakers manipulate the ratio of carbon dioxide to alcohol—usually with temperature and acidity--to control the rise time and the flavors in the breads.

Moist dough between 78 degrees and 80 degrees is an ideal environment for yeast growth. Since yeast is very sensitive to temperature, temperature is a major factor in how fast yeast multiples. Yeast is dormant and will not grow at 40 degrees and grows only slowly at 55 degrees. Yeast dies instantly at 140 degrees. We recommend not using water warmer than 120 degrees to avoid accidentally killing the yeast.

A thermometer has been called the baker’s secret weapon. In all breads, it is very useful to be able to measure the temperature of the water, the dough during mixing, and the bread as it comes from the oven. In using a bread machine, the exact water temperature is critical to a uniform outcome. Bread is baked when the internal temperature is between 190 degrees and 210 degrees. As mentioned, the ideal dough temperature for the proper growth of yeast is 78 to 80 degrees. At higher temperatures, the dough may rise too quickly creating a crumbly texture to the bread. At less, the bread will rise more slowly and will have a higher alcohol content—though some marvelous, complex flavors can be created at lower temperatures.

Might be due to temp. outside or sometimes if the yeast if old. You see baking is a precise art. You bread dough reacts to cold, hot and humid temp. Hence the difference.

your bread dough needs to be will devolped in the mixer to active the gluten that is in the flour your in igredients should always be room temp and what some people don't know is tha salt should never contact yeast beause the iodine is salt will kill your yeast

you could have killed the yeast with the liquid to warm or not activated the yeast with the liquid to cool. also the room temperature could be to cool or the yeast could be outdated.

Yeast is dated, sometimes you get old yeast.

sometimes the climate matters. Like I can make biscuits here, but not in DE. And sometimes if the air is moist it makes a difference

Did the humidity outside change?

Your water was probably to cold. It has to be luke warm.